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  • 101. Iacocca, Ezio
    et al.
    Heinonen, Olle
    Muduli, P. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Generation linewidth of mode-hopping spin torque oscillators2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 5, s. 054402-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experiments on spin torque oscillators commonly observe multimode signals. Recent theoretical works have ascribed the multimode signal generation to coupling between energy-separated spin wave modes. Here, we analyze in detail the dynamics generated by such mode coupling. We show analytically that the mode-hopping dynamics broaden the generation linewidth and makes it generally well described by a Voigt line shape. Furthermore, we show that the mode-hopping contribution to the linewidth can dominate, in which case it provides a direct measure of the mode-hopping rate. Due to the thermal drive of mode-hopping events, the mode-hopping rate also provides information on the energy barrier separating modes and temperature-dependent linewidth broadening. Our results are in good agreement with experiments, revealing the physical mechanism behind the linewidth broadening in multimode spin torque oscillators.

  • 102. Ivanov, A. V.
    et al.
    Bessarab, Pavel F.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Saint Petersburg State University, Russian Federation.
    Aksenova, E. V.
    Romanov, V. P.
    Uzdin, V. M.
    Energy surface and minimum energy paths for Fréedericksz transitions in bistable cholesteric liquid crystals2016Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 93, nr 4, artikkel-id 042708Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The multidimensional energy surface of a cholesteric liquid crystal in a planar cell is investigated as a function of spherical coordinates determining the director orientation. Minima on the energy surface correspond to the stable states with particular director distribution. External electric and magnetic fields deform the energy surface and positions of minima. It can lead to the transitions between states, known as the Fréedericksz effect. Transitions can be continuous or discontinuous depending on parameters of the liquid crystal which determine an energy surface. In a case of discontinuous transition when a barrier between stable states is comparable with the thermal energy, the activation transitions may occur, and it leads to the modification of characteristics of the Fréedericksz effect with temperature without explicit temperature dependencies of liquid crystal parameters. A minimum energy path between stable states on the energy surface for the Fréedericksz transition is found using the geodesic nudged elastic band method. Knowledge of this path, which has maximal statistical weight among all other paths, gives the information about a barrier between stable states and configuration of director orientation during the transition. It also allows one to estimate the stability of states with respect to the thermal fluctuations and their lifetime when the system is close to the Fréedericksz transition.

  • 103.
    Jokilaakso, Nima
    et al.
    KTH, Skolan för bioteknologi (BIO), Proteinteknologi.
    Afrasiabi, Roodabeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Larsson, Andréas
    KTH, Skolan för bioteknologi (BIO), Proteinteknologi.
    Björk, Per
    ACREO Swedish ICT.
    Schönberg, Tommy
    ACREO Swedish ICT.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Eriksson Karlström, Amelie
    KTH, Skolan för bioteknologi (BIO), Proteinteknologi.
    Spot-on functionalization of SiO2 for multiplexed silicon nanowire-FET biosensorsManuskript (preprint) (Annet vitenskapelig)
  • 104. Kamali, S.
    et al.
    Zha, Chaolin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yoda, Y.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Oxidation states and quality of upper interfaces in magnetic tunnel junctions: oxygen effect on crystallization of interfaces2014Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, nr 2, s. 026004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, we have deposited an Fe-57 sensor layer at the upper interface, i.e. the interface between the oxide barrier and the upper electrode in selected magnetic tunnel junctions (MTJs), in order to perform nuclear resonant scattering with the aim of obtaining direct information on the magnetic properties and quality of this interface. This is a unique approach as it makes use of this powerful technique to give information at the atomic level, and specifically from the interface where the sensor layer is deposited. By varying sample tunnel barrier thicknesses and oxidation times in the preparation of this barrier, we have observed that longer oxidation time results in not only an increase of the magnetic hyperfine fields, but also causes an interesting crystallization and smoothing of the interface. We also observed that boron atoms diffuse away from the lower part of the upper FeCoB electrode toward the capping layer. An important observation, which has a crucial effect in tunnel magnetoresistance values, is the absence of any magnetically dead FeO layer at the interface. Another finding is that the deposition of Fe on MgO is much smoother than the deposition of MgO on Fe.

  • 105. Kanerva, Mikko
    et al.
    Besharat, Zahra
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Livingston, Ryan
    Hallila, Harri
    Rutland, Mark
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Plasticity effects during the 4-point bending of intramedullary leg lengthening implants with telescopic structures2015Inngår i: M2D2015: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON MECHANICS AND MATERIALS IN DESIGN, INEGI-FEUP , 2015, s. 893-904Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A telescopic intramedullary leg lengthening implant during standard (ASTM F1264) four-point bend testing is analysed in this study. The structure of a telescopic implant is simulated using different finite element models in order to understand the ultimate bending behaviour. The surface morphology on the internal contact surfaces is also analysed using scanning electron microscopy and atomic force microscopy. The results show that the simulation of correct non-linear behaviour necessitates plastic material models and representative contacts between nested parts. Based on the microscopy analysis, the damage on the contact surfaces inside the locking mechanism of a real tested implant is not found critical in terms of probable crack nucleation sites.

  • 106. Keshavarz, S.
    et al.
    Kvashnin, Y. O.
    Di Marco, I.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Uppsala University, Sweden.
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Eriksson, O.
    Layer-resolved magnetic exchange interactions of surfaces of late 3d elements: Effects of electronic correlations2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 16, artikkel-id 165129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the results of an ab initio study of the magnetic properties of Fe, Co, and Ni surfaces. In particular, we discuss their electronic structure and magnetic exchange interactions (J(ij)), as obtained bymeans of a combination of density functional theory and dynamical mean-field theory. All studied systems have a pronounced tendency to ferromagnetism both for bulk and surface atoms. The presence of narrowband surface states is shown to enhance the magnetic moment as well as the exchange couplings. The most interesting results were obtained for the Fe surface where the atoms have a tendency to couple antiferromagnetically with each other. This interaction is relatively small when compared to interlayer ferromagnetic interaction, and it depends strongly on the lattice parameter. Local correlation effects are shown to lead to strong changes of the overall shape of the spectral functions. However, they seem not to play a decisive role in the overall picture of magnetic couplings studied here. We have also investigated the influence of correlations on the spin and orbital moments of bulklike and surface atoms. We found that dynamical correlations in general lead to enhanced values of the orbital moment.

  • 107.
    Kozhevnikov, V.
    et al.
    Tulsa Community College, Tulsa, Oklahoma 74119, USA.
    Suter, A.
    Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
    Fritzsche, H.
    Canadian Neutron Beam Centre, National Research Council Canada, Chalk River Laboratories, Ontario, Canada K0J1J0.
    Gladilin, V.
    TQC, Universiteit Antwerpen, 2610 Antwerpen, Belgium.
    Volodin, A.
    Laboratory of Solid-State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium.
    Moorkens, T.
    Laboratory of Solid-State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium.
    Trekels, M.
    Institute for Nuclear and Radiation Physics, KU Leuven, 3001 Leuven, Belgium.
    Cuppens, J.
    Laboratory of Solid-State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium.
    Wojek, Bastian M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Paul Scherrer Institute.
    Prokscha, T.
    Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
    Morenzoni, E.
    Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
    Nieuwenhuys, G. J.
    Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
    Van Bael, M. J.
    Laboratory of Solid-State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium.
    Temst, K.
    Institute for Nuclear and Radiation Physics, KU Leuven, 3001 Leuven, Belgium.
    Van Haesendonck, C.
    Laboratory of Solid-State Physics and Magnetism, KU Leuven, 3001 Leuven, Belgium.
    Indekeu, J. O.
    Institute for Theoretical Physics, KU Leuven, 3001 Leuven, Belgium.
    Nonlocal effect and dimensions of Cooper pairs measured by low-energy muons and polarized neutrons in type-I superconductors2013Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 87, nr 10, s. 104508-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Pippard coherence length xi(0) (the size of a Cooper pair) in two extreme type-I superconductors (In and Sn) was determined directly through high-resolution measurement of the nonlocal electrodynamic effect combining low-energy muon spin rotation spectroscopy and polarized neutron reflectometry. The renormalization factor Z = m*(cp)/2m (m*(cp) and m are the mass of the Cooper pair and the electron, respectively) resulting from the electron-phonon interaction, and the temperature-dependent London penetration depth lambda(L)(T) were determined as well. An expression linking xi(0), Z, and lambda(L)(0) is introduced and experimentally verified. This expression allows one to determine experimentally the Pippard coherence length in any superconductor, independent of whether the superconductor is local or nonlocal, conventional or unconventional.

  • 108. Kudrnovsky, J.
    et al.
    Drchal, V.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Rusz, J.
    Turek, I.
    Unified approach to electronic, thermodynamical, and transport properties of Fe3Si and Fe3Al alloys2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 13, s. 134408-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic, thermodynamical, and transport properties of ordered Fe3X (X = Al, Si) alloys are studied from first principles. We present here a unified approach to the phase stability, the estimate of the Curie temperature, the temperature dependence of sublattice magnetizations, magnon spectra, the spin-stiffnesses, and residual resistivities. An important feature of the present study is that all calculated physical properties are determined in the framework of the same first-principles electronic structure model combined with the effective Ising and Heisenberg Hamiltonians used for study of the thermodynamical properties of alloys. Curie temperatures, spin-stiffnesses, and magnon spectra are determined using the same calculated exchange integrals. Finally, the transport properties are calculated using the linear-response theory. Our theoretical estimates compare well with available experimental data. In particular, calculations predict (in agreement with experiment) the ordered D0(3) phase as the ground-state alloy structure, demonstrate that a correct relation of Curie temperatures of Fe3Al/Fe3Si alloys can be obtained only by going beyond a simple mean-field approximation, provide reasonable estimates of spin-stiffnesses, and give resistivities compatible with structural disorder observed in the experiment. Although the calculated temperature dependences of the Fe magnetization on different sublattices are similar, they nevertheless deviate more than in the experiment, and we discuss a possible origin.

  • 109.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses.

          STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers.

          All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs.

          In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.

  • 110.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Eklund, Anders
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Banuazizi, Seyed Amir Hossein
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Fallahi, Vahid Fallahi
    Faculty of Physics, Amirkabir University of Technology.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Yamanouchi, M.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Enobio, Eli C. I.
    Center for Spintronics Integrated Systems, Tohoku University.
    Ikeda, S.
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Ohno, Hideo
    Laboratory for Nanoelectronics and Spintronics, RIEC, Tohoku University.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Ultra-high frequency tunability in low-current and low-field spin-torque oscillators based on perpendicular magnetic tunnel junctionsManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We demonstrate ultra-high frequency tunability of up to 4.4 GHz/mA, and low threshold currents of about -21 $\mu$A, in spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions, in which both free and fixed layers have perpendicular magnetic anisotropy (PMA). By using different thicknesses of the two CoFeB layers, their individual PMA strengths can be tailored to achieve significant relative misalignment of their respective magnetizations in moderate in-plane fields. We observe a broad maximum in both the device resistance and the generated microwave power around maximum misalignment. Maximum frequency tunability is observed at low-to-moderate fields and decrease rapidly after maximum misalignment.

  • 111.
    Le, Quang Tuan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mazraati, Hamid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Nguyen, Thi Ngoc Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Bias dependence of parallel spin torque in all-perpendicular magnetic tunnel junction nanodevicesManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We performed spin-torque ferromagnetic resonance measurements on spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), with both free and fixed layers having perpendicular magnetic anisotropy, under the application of an in-plane field. A dc current between near-zero and -250 $\mu{A}$ was introduced to investigate the influence of spin-transfer torque effects on the asymmetric and symmetric components of the output voltage. Both components showed a minimum at a misalignment of about 30$^\circ$ between the magnetization of the two CoFeB layers, indicating a strong electric-field effect. We also found that the bias dependence of the spin-torque terms is in contrast to that of in-plane anisotropy CoFeB MTJs.

  • 112.
    Li, Fusheng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Li, Lin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Tong, Lianpeng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Daniel, Quentin
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Immobilization of a molecular catalyst on carbon nanotubes for highly efficient electro-catalytic water oxidation2014Inngår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, nr 90, s. 13948-13951Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrochemically driven water oxidation has been performed using a molecular water oxidation catalyst immobilized on hybrid carbon nanotubes and nano-material electrodes. A high turnover frequency (TOF) of 7.6 s(-1) together with a high catalytic current density of 2.2 mA cm(-2) was successfully obtained at an overpotential of 480 mV after 1 h of bulk electrolysis.

  • 113. Li, Xiaoqing
    et al.
    Schonecker, Stephan
    Simon, Eszter
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Zhang, Hualei
    Szunyogh, Laszlo
    Zhao, Jijun
    Johansson, Borje
    Vitos, Levente
    Tensile strain-induced softening of iron at high temperature2015Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikkel-id 16654Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In weakly ferromagnetic materials, already small changes in the atomic configuration triggered by temperature or chemistry can alter the magnetic interactions responsible for the non-random atomicspin orientation. Different magnetic states, in turn, can give rise to substantially different macroscopic properties. A classical example is iron, which exhibits a great variety of properties as one gradually removes the magnetic long-range order by raising the temperature towards its Curie point of T-C(degrees) = 1043 K. Using first-principles theory, here we demonstrate that uniaxial tensile strain can also destabilise the magnetic order in iron and eventually lead to a ferromagnetic to paramagnetic transition at temperatures far below T-C(degrees). In consequence, the intrinsic strength of the ideal single-crystal body-centred cubic iron dramatically weakens above a critical temperature of similar to 500 K. The discovered strain-induced magneto-mechanical softening provides a plausible atomic-level mechanism behind the observed drop of the measured strength of Fe whiskers around 300-500 K. Alloying additions which have the capability to partially restore the magnetic order in the strained Fe lattice, push the critical temperature for the strength-softening scenario towards the magnetic transition temperature of the undeformed lattice. This can result in a surprisingly large alloying-driven strengthening effect at high temperature as illustrated here in the case of Fe-Co alloy.

  • 114. Locht, I. L. M.
    et al.
    Kvashnin, Y. O.
    Rodrigues, D. C. M.
    Pereiro, M.
    Bergman, A.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Lichtenstein, A. I.
    Katsnelson, M. I.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Klautau, A. B.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala University, Sweden.
    Di Marco, I.
    Eriksson, O.
    Standard model of the rare earths analyzed from the Hubbard I approximation2016Inngår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, nr 8, artikkel-id 085137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work we examine critically the electronic structure of the rare-earth elements by use of the so-called Hubbard I approximation. From the theoretical side all measured features of both occupied and unoccupied states are reproduced, without significant deviations between observations and theory. We also examine cohesive properties like the equilibrium volume and bulk modulus, where we find, in general, a good agreement between theory andmeasurements. In addition, we have reproduced the spin and orbital moments of these elements as they are reflected from measurements of the saturation moment. We have also employed the Hubbard I approximation to extract the interatomic exchange parameters of an effective spin Hamiltonian for the heavy rare earths. We show that the Hubbard I approximation gives results which are consistent with calculations where 4f electrons are treated as core states for Gd. The latter approach was also used to address the series of the heavy/late rare earths. Via Monte Carlo simulations we obtained ordering temperatures which reproduce measurements within about 20%. We have further illustrated the accuracy of these exchange parameters by comparing measured and calculated magnetic configurations for the heavy rare earths and the magnon dispersion for Gd. The Hubbard I approximation is compared to other theories of the electronic structure, and we argue that it is superior. We discuss the relevance of our results in general and how this makes it possible to treat the electronic structure of materials containing rare-earth elements, such as permanent magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological insulators, and molecular magnets.

  • 115. Lodewijks, Kristof
    et al.
    Maccaferri, Nicolo
    Pakizeh, Tavakol
    Dumas, Randy K.
    Zubritskaya, Irina
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Vavassori, Paolo
    Dmitriev, Alexandre
    Magnetoplasmonic Design Rules for Active Magneto-Optics2014Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 14, nr 12, s. 7207-7214Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Light polarization rotators and nonreciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics, the combination of magnetism and plasmonics, is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range.

  • 116. Maccaferri, Nicolo
    et al.
    Berger, Andreas
    Bonetti, Stefano
    Bonanni, Valentina
    Kataja, Mikko
    Qin, Qi Hang
    van Dijken, Sebastiaan
    Pirzadeh, Zhaleh
    Dmitriev, Alexandre
    Nogues, Josep
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Vavassori, Paolo
    Tuning the Magneto-Optical Response of Nanosize Ferromagnetic Ni Disks Using the Phase of Localized Plasmons2013Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, nr 16, s. 167401-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We explore the influence of the phase of localized plasmon resonances on the magneto-optical activity of nanoferromagnets. We demonstrate that these systems can be described as two orthogonal damped oscillators coupled by the spin-orbit interaction. We prove that only the spin-orbit induced transverse plasmon plays an active role on the magneto-optical properties by controlling the relative amplitude and phase lag between the two oscillators. Our theoretical predictions are fully confirmed by magneto-optical Kerr effect and optical extinction measurements in nanostructures of different size and shape.

  • 117. Maccaferri, Nicolo
    et al.
    Gregorczyk, Keith E.
    de Oliveira, Thales V. A. G.
    Kataja, Mikko
    van Dijken, Sebastiaan
    Pirzadeh, Zhaleh
    Dmitriev, Alexandre
    Akerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Department of Physics, University of Gothenburg, Sweden .
    Knez, Mato
    Vavassori, Paolo
    Ultrasensitive and label-free molecular-level detection enabled by light phase control in magnetoplasmonic nanoantennas2015Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, artikkel-id 6150Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Systems allowing label-free molecular detection are expected to have enormous impact on biochemical sciences. Research focuses on materials and technologies based on exploiting localized surface plasmon resonances in metallic nanostructures. The reason for this focused attention is their suitability for single-molecule sensing, arising from intrinsically nanoscopic sensing volume and the high sensitivity to the local environment. Here we propose an alternative route, which enables radically improved sensitivity compared with recently reported plasmon-based sensors. Such high sensitivity is achieved by exploiting the control of the phase of light in magnetoplasmonic nanoantennas. We demonstrate a manifold improvement of refractometric sensing figure-of-merit. Most remarkably, we show a raw surface sensitivity (that is, without applying fitting procedures) of two orders of magnitude higher than the current values reported for nanoplasmonic sensors. Such sensitivity corresponds to a mass of similar to 0.8 ag per nanoantenna of polyamide-6.6 (n = 1.51), which is representative for a large variety of polymers, peptides and proteins.

  • 118. Maccaferri, Nicolo
    et al.
    Kataja, Mikko
    Bonanni, Valentina
    Bonetti, Stefano
    Pirzadeh, Zhaleh
    Dmitriev, Alexandre
    van Dijken, Sebastiaan
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Vavassori, Paolo
    Effects of a non-absorbing substrate on the magneto-optical Kerr response of plasmonic ferromagnetic nanodisks2014Inngår i: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 211, nr 5, s. 1067-1075Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetoplasmonics is an emerging field of intense research on materials combining magnetic and plasmonic functionalities. The novel optical and magneto-optical (MO) properties displayed by these materials could allow the design of a new class of magnetically controllable optical nano-devices. In this work, we investigate the effects of a non-absorbing (insulating) substrate on the MO activity of pure ferromagnetic disk-shaped nanostructures supporting localized plasmon resonances. We show that the red-shift of the localized plasmon resonance, related to the modification of the localization of the electromagnetic field due to the substrate, is not the only effect that the substrate has on the MO response. We demonstrate that the reflectivity of the substrate itself plays a key role in determining the MO response of the system. We discuss why it is so and provide a description of the modeling tools suitable to take into account both effects. Understanding the role of the substrate will permit a more aware design of magnetoplasmonic nanostructured devices for future biotechnological and optoelectronic applications. [GRAPHICS] Ferromagnetic nickel nanodisk in vacuum (left) and on a non-absorbing substrate (right), illuminated by linearly polarized light. The polarization of the reflected field is changed in the first case due to a combination of intrinsic magneto-optical properties and the nanoconfinement of the material. In the second case, the polarization of the reflected light is affected also by the presence of the substrate.

  • 119. Madami, M.
    et al.
    Iacocca, E.
    Sani, S
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gubbiotti, G.
    Tacchi, S.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Gothenburg University.
    Carlotti, G.
    Propagating spin waves excited by spin-transfer torque: A combined electrical and optical study2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 2, artikkel-id 024403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanocontact spin-torque oscillators are devices in which the generation of propagating spin waves can be sustained by spin transfer torque. In the present paper, we perform combined electrical and optical measurements in a single experimental setup to systematically investigate the excitation of spin waves by a nanocontact spin-torque oscillator and their propagation in a Ni80Fe20 extended layer. By using microfocused Brillouin light scattering we observe an anisotropic emission of spin waves, due to the broken symmetry imposed by the inhomogeneous Oersted field generated by the injected current. In particular, spin waves propagate on the side of the nanocontact where the Oersted field and the in-plane component of the applied magnetic field are antiparallel, while propagation is inhibited on the opposite side. Moreover, propagating spin waves are efficiently excited only in a limited frequency range corresponding to wavevectors inversely proportional to the size of the nanocontact. This frequency range obeys the dispersion relation for exchange-dominated spin waves in the far field, as confirmed by micromagnetic simulations of similar devices. The present results have direct consequences for spin wave based applications, such as synchronization, computation, and magnonics.

  • 120.
    Marinins, Aleksandrs
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO.
    Yan, Zhenyu
    Chen, Hongzheng
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Veinot, Jonathan G. C.
    Popov, Sergei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Photostable Polymer/Si Nanocrystal Bulk Hybrids with Tunable Photoluminescence2016Inngår i: ACS Photonics, E-ISSN 2330-4022, Vol. 3, nr 9, s. 1575-1580Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid polymer/Si nanocrystal bulk nanocomposites were fabricated from solutions of alkene- and hydride-terminated silicon nanocrystals (NCs) in toluene. The photoluminescence peak position of hydride-terminated SiNCs before polymerization was tuned by photoassisted hydrofluoric acid etching. Optical properties of obtained PMMA/NC hybrids, such as quantum yield, luminescence lifetime, and dispersion factor, were evaluated over time. Photostability of these transparent bulk polymer/SiNC hybrids over months was confirmed. The emission covers the visible to near-infrared range with a quantum yield of similar to 30-40% for yellow-red nanocomposites.

  • 121. Martynova, Y.
    et al.
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sachert, S.
    Polzin, S.
    Widdra, W.
    Shaikhutdinov, S.
    Freund, H. -J
    CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111)2013Inngår i: Catalysis Letters, ISSN 1011-372X, E-ISSN 1572-879X, Vol. 143, nr 11, s. 1108-1115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOx ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (similar to 10(-6) mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:O-2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction.

  • 122. Matt, C. E.
    et al.
    Fatuzzo, C. G.
    Sassa, Y.
    Mansson, M.
    Fatale, S.
    Bitetta, V.
    Shi, X.
    Pailhes, S.
    Hårdensson Berntsen, Magnus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Kurosawa, T.
    Oda, M.
    Momono, N.
    Lipscombe, O. J.
    Hayden, S. M.
    Yan, J. -Q
    Zhou, J. -S
    Goodenough, J. B.
    Pyon, S.
    Takayama, T.
    Takagi, H.
    Patthey, L.
    Bendounan, A.
    Razzoli, E.
    Shi, M.
    Plumb, N. C.
    Radovic, M.
    Grioni, M.
    Mesot, J.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Stockholm University, Sweden.
    Chang, J.
    Electron scattering, charge order, and pseudogap physics in La1.6-xNd0.4SrxCuO4: An angle-resolved photoemission spectroscopy study2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, nr 13, artikkel-id 134524Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report an angle-resolved photoemission study of the charge stripe ordered La1.6-xNd0.4SrxCuO4 (Nd-LSCO) system. A comparative and quantitative line-shape analysis is presented as the system evolves from the overdoped regime into the charge ordered phase. On the overdoped side (x = 0.20), a normal-state antinodal spectral gap opens upon cooling below 80 K. In this process, spectral weight is preserved but redistributed to larger energies. A correlation between this spectral gap and electron scattering is found. A different line shape is observed in the antinodal region of charge ordered Nd-LSCO x = 1/8. Significant low-energy spectral weight appears to be lost. These observations are discussed in terms of spectral-weight redistribution and gapping originating from charge stripe ordering.

  • 123.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Free- and reference-layer magnetization modes vs.~in-plane magnetic field in  a magnetic tunnel junction with perpendicular magnetic easy axis2016Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  • 124.
    Mazraati, Hamid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden.
    Le, Tuan Q.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Awad, Ahmad A.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. University of Gothenburg, Sweden.
    Hirayama, Eriko
    Ikeda, Shoji
    Matsukura, Fumihiro
    Ohno, Hideo
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. NanOsc AB, Sweden; University of Gothenburg, Sweden.
    Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis2016Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 10, artikkel-id 104428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  • 125.
    Metaferia, Wondwosen
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Dev, Apurba
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Kataria, Himanshu
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Junesand, Carl
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Sun, Yanting
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Anand, Srinivasan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    Tommila, Juha
    Pozina, Galia
    Hultman, Lars
    Guina, Mircea
    Niemi, Tapio
    Lourdudoss, Sebastian
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Halvledarmaterial, HMA.
    High quality InP nanopyramidal frusta on Si2014Inngår i: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, nr 21, s. 4624-4632Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanosized octagonal pyramidal frusta of indium phosphide were selectively grown at circular hole openings on a silicon dioxide mask deposited on indium phosphide and indium phosphide pre-coated silicon substrates. The eight facets of the frusta were determined to be {111} and {110} truncated by a top (100) facet. The size of the top flat surface can be controlled by the diameter of the openings in the mask and the separation between them. The limited height of the frusta is attributed to kinetically controlled selective growth on the (100) top surface. Independent analyses with photoluminescence, cathodoluminescence and scanning spreading resistance measurements confirm certain doping enrichment in the frustum facets. This is understood to be due to crystallographic orientation dependent dopant incorporation. The blue shift from the respective spectra is the result of this enrichment exhibiting the Burstein-Moss effect. Very bright panchromatic cathodoluminescence images indicate that the top surfaces of the frusta are free from dislocations. The good optical and morphological quality of the nanopyramidal frusta indicates that the fabrication method is very attractive for the growth of site-, shape-, and number-controlled semiconductor quantum dot structures on silicon for nanophotonic applications.

  • 126.
    Mirsakiyeva, Amina
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Quantum Mechanical Calculations of Thermoelectrical Polymers and Organic Molecules2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The subject of the present licentiate thesis is density functional theorybased electronic structure calculations of organic thermoelectric materials and novel organic molecules. We used the Car-Parrinello molecular dynamics method in order to investigate the electronic structure of “green energy” and “greenchemistry” compounds.

    First, we have investigated the electronic structure of the poly(3,4-ethylene-dioxythiophene) (PEDOT) and its derivatives - the best studied and successfully implemented by industry organic thermoelectric material. Its transparency, low toxicity and high stability in the oxidized state are combined withan ability to produce electrical current when applying a temperature gradient. This makes PEDOT a perfect “organic metal” and a first candidate for organic thermoelectrogenerators - devices that can produce “green energy” from a temperature difference. The average structures found in these quantum dynamical simulations agree well with earlier static electronic structure studies. The energy gap of two, four and six unit oligomers of PEDOT was calculated and was found to lie in the range of previous theoretical studies. We have also calculatedthe point-charge distributions along the polymer backbone in order to investigate the polaron formed by doping agents of PEDOT. Our analysis allowed us to predict possible localization of the charge in the center of the polymer chain. However, further calculations of the twelve unit PEDOT and its selenium and tellurium derivatives will provide more information. First-principles calculations for the tellurium derivative of PEDOT are here presented for the first time.

    The second part of our investigation concerns theoretical calculations of novel piperidine-containing acetylene glycols. These molecules were newly synthesized by our experimental collaborators and are expected to provideplant growth stimulation properties, the same as its diacetylene analogs. We performed quantum mechanical calculations of four compounds, presented ananalysis of the highest occupied and lowest unoccupied molecular orbitals and collected detailed information on point-charges for further parametrization of novel molecules for future computational studies. According to these results, the low production yield found in the experiments cannot be attributed to chemical instability in these novel compounds.

  • 127.
    Mirsakiyeva, Amina
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Botkina, D.
    Elgammal, Karim
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ten, Assel
    Hugosson, Håkan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Yu, Valentina
    Experimental and ab initio studies of the novel piperidine-containing acetylene glycolsManuskript (preprint) (Annet vitenskapelig)
  • 128.
    Mirsakiyeva, Amina
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Kazakh-British Technical University, Kazakhstan.
    Botkina, Darya
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion. Institute of Chemical Sciences, Kazakhstan.
    Elgammal, Karim
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Ten, Assel
    Hugosson, Håkan W.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Yu, Valentina
    Experimental and density functional theory studies of some novel piperidine-containing acetylene glycols2016Inngår i: ARKIVOC, ISSN 1551-7004, E-ISSN 1551-7012, s. 86-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Synthesis routes of novel piperidine-containing acetylenes are presented. The new molecules are expected to exhibit plant growth stimulation properties. In particular, the yield in a situation of drought is expected to increase. Our synthesis makes use of the Favorskii reaction between cyclohexanone/piperidone and triple-bond containing alcohols. The structures of the obtained molecules were determined using nuclear magnetic resonance (NMR). The electronic structure and geometries of the molecules were studied theoretically using first-principles calculations based on density functional theory. The calculated geometries agree very well with the experimentally determined ones, and also allow us to determine bond lengths, angles and charge distributions inside the molecules.

  • 129.
    Mohseni, Seyed Majid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Redjai Sani, Sohrab
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Dumas, R. K.
    Persson, J.
    Nguyen, Thi Ngooc Ahn
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Pogoryelov, Ye.
    Muduli, P. K.
    Iacocca, E.
    Eklund, A.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Magnetic droplet solitons in orthogonal nano-contact spin torque oscillators2014Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 435, s. 84-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study microwave signal generation as a function of drive current and applied perpendicular magnetic Field in nano contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has strong easy plane anisotropy, and the [Co/Nil free layer has a strong perpendicular magnetic anisotropy. The orthogonal NC-STOs exhibit a dramatic transition from the conventional ferromagnetic resonance like spin wave mode to a magnetic droplet solilon mode. In particular, the field and current dependence of the droplet solilon near threshold are discussed. Near threshold the droplet solilon undergoes complex dynamics that include mode hopping, as evident in the experimental frequency domain and rnagneloresislance response.

  • 130. Mohseni, Seyed Morteza
    et al.
    Hamdi, M.
    Yazdi, H. F.
    Banuazizi, S. Amir Hossein
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Redjai Sani, Sohrab
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Materialfysik, MF (Stängd 20120101).
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    Magnetic droplet soliton nucleation in oblique fields2018Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 97, nr 184402Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the auto-oscillating magnetodynamics in orthogonal spin-torque nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic-field angle. In perpendicular fields and at OOP field angles down to approximately 50°, we observe the nucleation of a droplet. However, for field angles below 50°, experiments indicate that the droplet gives way to propagating spin waves, in agreement with our micromagnetic simulations. Theoretical calculations show that the physical mechanism behind these observations is the sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show that the presence of a strong perpendicular magnetic anisotropy free layer in the system reverses the angular dependence of the SWN and dynamics in STNOs with respect to the known behavior determined for the in-plane magnetic anisotropy free layer. Our results are of fundamental interest in understanding the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.

  • 131. Moradi, Mehrdad
    et al.
    Mohseni, Seyed Majid
    Mahmoodi, Saman
    Rezvani, Davood
    Ansari, Narges
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Au/NiFe Magnetoplasmonics: Large Enhancement of Magneto-Optical Kerr Effect for Magnetic Field Sensors and Memories2015Inngår i: Electronic Materials Letters, ISSN 1738-8090, Vol. 11, nr 3, s. 440-446Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface plasmon polariton resonance (SPPR) can be originated from the surface charge oscillation via light localization at the interface of a metal, for example, Au or Ag and a dielectric. Such localization can be implemented to increase the magneto-optical (MO) activity of a magnetic medium while SPPR is fulfilled, which is known as magnetoplasmonics. In this paper, a magnetoplasmonic bilayer of Au/NiFe (Py) sputter deposited on glass is demonstrated. Large enhancement in MO-Ken effedt (MOKE) response due to SPPR effect is observed at different light incident angles. By measuring and analyzing the MO signals from the sample with different thicknesses of Au and Py layers, the optimal thicknesses' range is obtained with the largest MOKE. The large MOKE intensity from ultra-soft magnetic Py layer with low coercivity and small saturation field suggests a weak magnetic field-sensitive MO-based element. Finally, different applications of such structures, for example, weak magnetic field sensors and magnetic multilevel memory elements are demonstrated.

  • 132. Morrison, C.
    et al.
    Miles, J. J.
    Nguyen, T. N. Anh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Fang, Y.
    Dumas, R. K.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Thomson, T.
    Exchange coupling in hybrid anisotropy magnetic multilayers quantified by vector magnetometry2015Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 17, artikkel-id 17B526Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hybrid anisotropy thin film heterostructures, where layers with perpendicular and in-plane anisotropy are separated by a thin spacer, are novel materials for zero/low field spin torque oscillators and bit patterned media. Here, we report on magnetization reversal and exchange coupling in a archetypal Co/Pd (perpendicular)-NiFe (in-plane) hybrid anisotropy system studied using vector vibrating sample magnetometry. This technique allows us to quantify the magnetization reversal in each individual magnetic layer, and measure of the interlayer exchange as a function of non-magnetic spacer thickness. At large (>1 nm) spacer thicknesses Ruderman-Kittel-Kasuya-Yosida-like exchange dominates, with orange-peel coupling providing a significant contribution only for sub-nm spacer thickness.

  • 133. Moskalenko, Mariia
    et al.
    Bessarab, Pavel F.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. St. Petersburg State University, Russian Federation.
    Uzdin, Valery M.
    Jonsson, Hannes
    Qualitative insight and quantitative analysis of the effect of temperature on the coercivity of a magnetic system2016Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 6, nr 2, artikkel-id 025213Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The temperature dependence of the response of a magnetic system to an applied field can be understood qualitatively by considering variations in the energy surface characterizing the system and estimated quantitatively with rate theory. In the system analysed here, Fe/Sm-Co spring magnet, the width of the hysteresis loop is reduced to a half when temperature is raised from 25 K to 300 K. This narrowing can be explained and reproduced quantitatively without invoking temperature dependence of model parameters as has typically been done in previous data analysis. The applied magnetic field lowers the energy barrier for reorientation of the magnetization but thermal activation brings the system over the barrier. A 2-dimensional representation of the energy surface is developed and used to gain insight into the transition mechanism and to demonstrate how the applied field alters the transition path. Our results show the importance of explicitly including the effect of thermal activation when interpreting experiments involving the manipulation of magnetic systems at finite temperature.

  • 134. Muduli, P. K.
    et al.
    Heinonen, O. G.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bias dependence of perpendicular spin torque and of free- and fixed-layer eigenmodes in MgO-based nanopillars2011Inngår i: Physical Review B - Condensed Matter and Materials Physics, ISSN 1098-0121, Vol. 83, nr 18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have measured the bias voltage and field dependence of eigenmode frequencies in a magnetic tunnel junction with MgO barrier. We show that both free layer (FL) and reference layer (RL) modes are excited, and that a crossover between these modes is observed by varying external field and bias voltage. The bias voltage dependence of the FL and RL modes are shown to be dramatically different. The bias dependence of the FL modes is linear in bias voltage, whereas that of the RL mode is strongly quadratic. Using modeling and micromagnetic simulations, we show that the linear bias dependence of FL frequencies is primarily due to a linear dependence of the perpendicular spin torque on bias voltage, whereas the quadratic dependence of the RL on bias voltage is dominated by the reduction of exchange bias due to Joule heating, and is not attributable to a quadratic dependence of the perpendicular spin torque on bias voltage.

  • 135. Mukherjee, Sumanta
    et al.
    Knut, Ronny
    Mohseni, S. Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Anh Nguyen, T. N.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. VNU HCM, Vietnam.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Persson, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sahoo, Anindita
    Hazarika, Abhijit
    Pal, Banabir
    Thiess, Sebastian
    Gorgoi, Mihaela
    Kumar, P. S. Anil
    Drube, Wolfgang
    Karis, Olof
    Sarma, D. D.
    Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions2015Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, nr 8, artikkel-id 085311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

  • 136. Månsson, M.
    et al.
    Pra, K.
    Sassa, Y.
    Tobash, P. H.
    Bauer, E. D.
    Rusu, C.
    Andreica, D.
    Tjernberg, Oscar
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sedlak, K.
    Grioni, M.
    Durakiewicz, T.
    Sugiyama, J.
    Magnetic order in the 2D Heavy-Fermion system CePt2In7 studied by μ+SR2014Inngår i: 13TH INTERNATIONAL CONFERENCE ON MUON SPIN ROTATION, RELAXATION AND RESONANCE, 2014, Vol. 551, nr 1, s. 012028-, artikkel-id 012028Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The low-temperature microscopic magnetic properties of the quasi-2D heavy- fermion compound, CePt2In7 are investigated by using a positive muon-spin rotation and relaxation (μ+SR) technique. Clear evidence for the formation of a commensurate antiferromagnetic order below TN 5.40 K is presented. The magnetic order parameter is shown to fit well to a modified BCS gap-energy function in a strong-coupling scenario.

  • 137. Nag, Abhishek
    et al.
    Middey, S.
    Bhowal, Sayantika
    Panda, S. K.
    Mathieu, Roland
    Orain, J. C.
    Bert, F.
    Mendels, P.
    Freeman, P. G.
    Månsson, Martin
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
    Ronnow, H. M.
    Telling, M.
    Biswas, P. K.
    Sheptyakov, D.
    Kaushik, S. D.
    Siruguri, Vasudeva
    Meneghini, Carlo
    Sarma, D. D.
    Dasgupta, Indra
    Ray, Sugata
    Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O92016Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, nr 9, artikkel-id 097205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

  • 138.
    Najmoddin, Najmeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Beitollahi, Ali
    Devlin, Eamonn
    Kavas, Huseyin
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Niarchos, Dimitris
    Rezaie, Hamidreza
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Magnetic properties of crystalline mesoporous Zn-substituted copper ferrite synthesized under nanoconfinement in silica matrix2014Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 190, s. 346-355Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of ordered mesoporous single phase Cu1-xZnxFe2O4 spinel ferrites, with x ranging from 0.00 to 0.75 with a step increment of 0.25, are prepared by a novel nanocasting route with the aid of vinyl-functionalized mesoporous silica as a hard template. All samples display a relatively high surface area and narrow pore size distribution from nitrogen sorption analysis. The magnetic hysteresis loops of these samples measured at 300 K, the temperature dependence of the zero field cooled (ZFC) and field cooled (FC) magnetization curves and the Mossbauer Spectra show the presence of superparamagnetic nanopartides in all samples. The hysteresis data indicate that the maximum saturation magnetization of 52 emu g(-1), is obtained for the composition with x = 0.25. For x >= 0.5, the saturation magnetization decreases as a result of the cation redistribution within tetrahedral (A) and octahedral (B) sites which weakens the A-B interactions due to triangular Yafet-Kittel spin arrangement on the B-sublattice. The observed magnetic features are attributed to the confined spaces of the host material which acts as a nanoreactor, limiting the growth of the embedded oxide phase and significantly influencing the cation distribution of copper-zinc ferrite on the A and B sites.

  • 139.
    Najmoddin, Najmeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Beitollahi, Ali
    Kavas, Huseyin
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Rezaie, Hamidreza
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    XRD cation distribution and magnetic properties of mesoporous Zn-substituted CuFe2O42014Inngår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 40, nr 2, s. 3619-3625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of Zn doping on magnetic properties of mesoporous CuFe2O4 has been investigated. The cation distribution amongst tetrahedral (A) and octahedral (B) sites of the lattice has been calculated analytically by X-ray diffraction (XRD), using the Bertaut method. The results reveal that these ferrites belong to the family of mixed or partially inverse spinels and Zn2+ ions occupy mainly the A site while Cu2+ ions have more tendency for the B-site. The magnetic moments estimated from cation distribution do not coincide with the magnetization data obtained from the SQUID-VSM technique. This is attributed to the core shell structure of nanoparticles and non-collinearity of spins at the surface or spin canting in the sublattices of Zn-substituted CuFe2O4 nanoparticles. The temperature dependence of the zero field cooled (ZFC) and field cooled (PC) magnetization curves of mesoporous Cu0.75Zn0.25Fe2O4 confirms the presence of superparamagnetic phase at room temperature.

  • 140.
    Najmoddin, Najmeh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Beitollahi, Ali
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Ansari, Narges
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Devlin, Eamonn
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik (Stängd 20120101), Materialfysik, MF (Stängd 20120101).
    Rezaie, Hamidreza
    Niarchos, Dimitris
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Effect of nanoconfinement on the formation, structural transition and magnetic behavior of mesoporous copper ferrite2014Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 598, s. 191-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Superparamagnetic, cubic single phase, ordered mesoporous copper ferrite is synthesized through confinement in nanocages of mesoporous silica. The heat generated during the reaction is conserved in the silica template pore channels, which allows the formation of copper ferrite at a relatively low processing temperature. The Jahn-Teller distortion is suppressed due to the effect of nanoconfinement and thus the high temperature phase of cubic copper ferrite is stabilized at room temperature. The particle size obtained from TEM, the crystallite size calculated from XRD and the magnetic domain size estimated from magnetization measurements are all in good agreement, manifesting the significant role of the confinement in the growth and fabrication of crystalline, single magnetic domain, nanoparticles with superparamagnetic behavior at room temperature.

  • 141.
    Nguyen, T. N. Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ Ho Chi Minh City, Vietnam.
    Knut, R.
    Fallahi, V.
    Chung, Sunjae
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Le, Quang Tuan Le
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, S. M.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Karis, O.
    Peredkov, S.
    Dumas, R. K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs2014Inngår i: PHYS REV APPL, ISSN 2331-7019, Vol. 2, nr 4, s. 044014-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.

  • 142.
    Nguyen, Thi Ngoc Anh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Vietnam Natl Univ, Vietnam.
    Fallahi, Vahid
    Le, Quang Tuan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Chung, Sunjea
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Shahid Beheshti Univ, Iran.
    Dumas, Randy K.
    Miller, Casey W.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Investigation of the Tunability of the Spin Configuration Inside Exchange Coupled Springs of Hard/Soft Magnets2014Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, nr 6, s. 2004906-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic multilayer (ML) structures comprising a perpendicular magnetic anisotropy (PMA) layer coupled to an in-plane magnetic anisotropy (IMA) layer are promising materials for zero/low field operating spin-torque oscillators and bit patterned recording media. The magnetization tilt angle can be easily tuned by varying the IMA layer thickness due to the competition between PMA and IMA layers. To explore the underlying magnetization reversal mechanism and to further understand the control of tilt angle and uniformity of the magnetization, the IMA (NiFe, Co, and CoFeB)/PMA (Co/Pd MLs) exchange spring systems are systematically studied. Experimental data obtained from magnetometry show good agreement with 1-D micromagnetic simulations, allowing us to design tunable exchange coupled spring as a function of IMA thickness.

  • 143. Nosikov, I. A.
    et al.
    Bessarab, Pavel
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Klimenko, M. V.
    Klimenko, V. V.
    Bessarab, F. S.
    Kotova, D. S.
    Zakharov, V. E.
    Testing the method of transverse displacements for calculating paths of the HF radio wave propagation in three dimensional inhomogeneous media2015Inngår i: 2015 1st URSI Atlantic Radio Science Conference, URSI AT-RASC 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, artikkel-id 7303091Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Propagation of the Russian Academy of Sciences (WD IZMIRAN), Kaliningrad, Russia There are two approaches for radio wave ray tracing when the endpoints of the ray are fixed. The standard approach is the shooting method where a ray is sent out in some direction and its landing point is used to modify the shooting direction and obtain the desired endpoint. However, there is no systematic, universal algorithm for refining the shooting direction. Another approach is based on direct utilization of the variational principle for the optical path (Fermat’s principle). The idea is to transform an arbitrary trajectory to an optimal one, while the endpoints of the trajectory are kept fixed according to the boundary conditions.

  • 144.
    Pan, Fan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gilbert damping of doped permalloy from first principles calculations2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The dynamic process of how fast a spintronic device can be switched from one state to another is characterized by the Gilbert damping parameter. It has been found that the Gilbert damping along with other intrinsic properties in permalloy, can be tuned by different dopants and doping concentration. Therefore, a study of intrinsic magnetic properties with emphasis on the dependence of the Gilbert damping parameter from first principles calculations is investigated. It is aimed at to give an insight of the microscopic understanding originated from electronic structure and to provide a guideline in the practical spintronic design. The topic of the present thesis is to investigate, by means of first principle calculations, how the variation of the Gilbert damping parameter depends upon the electronic structure of pure and doped permalloy. We show that the Gilbert damping has a monotonic increase with the doping concentration due to an increasing amount of scattering processes. The dopants of the 5d transition metal give rise to a much larger impact than the 4d, as the spin orbit coupling effect is more pronounced in the heavy elements. Our results are in satistying agreement with experiment.

  • 145. Panda, S. K.
    et al.
    Bhowal, S.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Eriksson, O.
    Dasgupta, I.
    Effect of spin orbit coupling and Hubbard U on the electronic structure of IrO22014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 15, s. 155102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied in detail the electronic structure of IrO2 including spin orbit coupling (SOC) and electronelectron interaction, both within the generalized gradient approximation plus Hubbard U (GGA+ U) and GGA plus dynamical mean field theory (GGA+ DMFT) approximations. Our calculations reveal that the Ir t(2g) states at the Fermi level largely retain the J(eff) = 1/2 character, suggesting that this complex spin orbit entangled state may be robust even in metallic IrO2. We have calculated the phase diagram for the ground state of IrO2 as a function of U and find a metal insulator transition that coincides with a magnetic phase change, where the effect of SOC is only to reduce the critical values of U necessary for the transition. We also find that dynamic correlations, as given by the GGA+ DMFT calculations, tend to suppress the spin- splitting, yielding a Pauli paramagnetic metal for moderate values of the Hubbard U. Our calculated optical spectra and photoemission spectra including SOC are in good agreement with experiment, demonstrating the importance of SOC in IrO2.

  • 146. Panda, S. K.
    et al.
    Di Marco, I.
    Delin, Anna
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Eriksson, O.
    Correlated electronic structure of CeN2016Inngår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 208, s. 111-115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied in detail the electronic structure of CeN including spin orbit coupling (SOC) and electron electron interaction, within the dynamical mean-field theory combined with density-functional theory in generalized gradient approximation (GGA+DMFT). The effective impurity problem has been solved through the spin-polarized T-matrix fluctuation-exchange (SPTF) solver and the Hubbard I approximation (HIA). The calculated l-projected atomic partial densities of states and the converged potential were used to obtain the X-ray-photoemission-spectra (XPS) and Bremstrahlung Isochromat spectra (BIS). Following the spirit of Gunnarsson-Schonhammer model, we have coupled the SPTF and HIA 4f spectral functions to explain the various spectroscopic manifestations of CeN. Our computed spectra in such a coupled scheme explain the experimental data remarkably well, establishing the validity of our theoretical model in analyzing the electronic structure of CeN. The contribution of the various l-states in the total spectra and the importance of cross sections are also analyzed in detail.

  • 147. Panda, S. K.
    et al.
    Pal, Banabir
    Mandal, Suman
    Gorgoi, Mihaela
    Das, Shyamashis
    Sarkar, Indranil
    Drube, Wolfgang
    Sun, Weiwei
    Di Marco, I.
    Lindblad, Andreas
    Thunstroem, P.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Karis, Olof
    Kvashnin, Y. O.
    van Schilfgaarde, M.
    Eriksson, O.
    Sarma, D. D.
    High photon energy spectroscopy of NiO: Experiment and theory2016Inngår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, nr 23, artikkel-id 235138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have revisited the valence band electronic structure of NiO by means of hard x-ray photoemission spectroscopy (HAXPES) together with theoretical calculations using both the GW method and the local density approximation + dynamical mean-field theory (LDA+DMFT) approaches. The effective impurity problem in DMFT is solved through the exact diagonalization (ED) method. We show that the LDA+DMFT method in conjunction with the standard fully localized limit (FLL) and around mean field (AMF) double-counting alone cannot explain all the observed structures in the HAXPES spectra. GW corrections are required for the O bands and Ni-s and p derived states to properly position their binding energies. Our results establish that a combination of the GW and DMFT methods is necessary for correctly describing the electronic structure of NiO in a proper ab initio framework. We also demonstrate that the inclusion of photoionization cross section is crucial to interpret the HAXPES spectra of NiO. We argue that our conclusions are general and that the here suggested approach is appropriate for any complex transition metal oxide.

  • 148. Panda, S. K.
    et al.
    Thunstrom, P.
    Di Marco, I.
    Schott, J.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Dasgupta, I.
    Eriksson, O.
    Sarma, D. D.
    A charge self-consistent LDA plus DMFT study of the spectral properties of hexagonal NiS2014Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, s. 093049-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure and spectral properties of hexagonal NiS have been studied in the high temperature paramagnetic phase and low temperature anti-ferromagnetic phase. The calculations have been performed using charge self-consistent density-functional theory in local density approximation combined with dynamical mean-field theory (LDA+DMFT). The photoemission spectra (PES) and optical properties have been computed and compared with the experimental data. Our results show that the dynamical correlation effects are important to understand the spectral and optical properties of NiS. These effects have been analyzed in detail by means of the computed real and imaginary part of the self-energy.

  • 149. Parra, Erick O. Burgos
    et al.
    Bukin, Nick
    Dupraz, Maxime
    Beutier, Guillaume
    Sani, Sohrab Redjai
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Popescu, Horia
    Cavill, Stuart A.
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Univ Gothenburg, Sweden.
    Jaouen, Nicolas
    Keatley, Paul S.
    Hicken, Robert J.
    van der Laan, Gerrit
    Ogrin, Feodor Y.
    Holographic Magnetic Imaging of Single-Layer Nanocontact Spin-Transfer Oscillators2016Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 52, nr 7, artikkel-id 6500304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Time-averaged images of the magnetization within single-layer spin-transfer oscillators have been obtained using the holography with extended reference by autocorrelation linear differential operator technique. Transport measurements on a Pd(5)-Cu(20)-Ni81Fe19(7)-Cu(2)-Pd(2) (in nanometers) stack with a 100 nm diameter nanocontact reveal the presence of vortex dynamics. Magnetic images of the device for injected current values of 24 and -24 mA suggest that a vortex has been ejected from the nanocontact and become pinned at the edge of the region that is visible through the Au mask.

  • 150.
    Persson, Johan
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sani, Sohrab Redjai
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Bonetti, Stefano
    Magnusson, Fredrik
    Pogorylov, Yevgen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Mohseni, Seyed Majid
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Gunnarsson, Sten
    Norling, Martin
    Stoij, Christer
    Åkerman, Johan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Spin-Torque Oscillator in an Electromagnet Package2012Inngår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 48, nr 11, s. 4378-4381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spin-torque oscillators (STO) hold promise for multi-octave frequency operation at very high frequencies and modulation speeds. STO operation is typically demonstrated using large electromagnets and probe stations, and has so far not been packaged with a portable form factor. For STOs to be utilized in real applications, a smaller packaging solution is needed. We integrate STOs with packages originally developed for YIG oscillators, modified to incorporate permanent magnets and to achieve a compact portable oscillator based on the STO.

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