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  • 51.
    Khartsev, Sergiy
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, A. M.
    High performance Bi3Fe5O12/Sm3Ga5O12 (m) magneto-optical photonic crystals2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 5Article in journal (Refereed)
    Abstract [en]

    We report the properties of one-dimensional heteroepitaxial all-garnet magneto-optical (MO) photonic crystals (MOPCs) composed of alternating MO-active Bi3Fe5O12 (BIG) and transparent Sm3Ga5O12 (SGG) quarter-wavelength layers grown by rf-magnetron sputtering on Ca,Mg,Zr:Gd3Ga5O12(111) and Gd3Sc2Ga3O12(001) crystals. MOPCs' spectra, as designed, exhibit a stop band structure and a band gap with the transmittance central peak at 750 nm caused by light localization in the half-wavelength BIG cavity. A series of MOPCs with different numbers of [BIG/SSG](m) reflectors (m=4, 5, and 6) has been fabricated to optimize the specific Faraday rotation theta(F) (deg/mu m) and MO-quality factor Q(deg)=2 parallel to theta(F)parallel to/absorption coefficient. A close BIG-to-SGG lattice match enabled significant improvement of [Bi3Fe5O12/Sm3Ga5O12](m) properties compared to previously reported [Bi3Fe5O12/Y3Fe5O12](m) [S. Kahl and A. M. Grishin, Appl. Phys. Lett. 84, 1438 (2004)] and [Bi3Fe5O12/Gd3Ga5O12](m) [S. I. Khartsev and A. M. Grishin, Alexander M.

  • 52.
    Khartsev, Sergiy
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Bi3Fe5O12/Gd3Ga5O12 (m) magneto-optical photonic crystals2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 12Article in journal (Refereed)
    Abstract [en]

    A series of one-dimensional heteroepitaxial all-garnet magneto-optical photonic crystals has been synthesized and optically characterized. They are composed of alternating magneto-optically active Bi3Fe5O12 (BIG) and Gd3Ga5O12 (GGG) quarter-wave length layers pulsed laser deposited on to the GGG(001) substrate. Photonic crystals, as designed, exhibit stop band structure and the band gap with the transmittance central peak caused by the light localization in the half-wave length BIG cavity. Compared to previously reported [Bi3Fe5O12/Y3Fe5O12](m) photonic crystal [Appl. Phys. Lett. 84, 1438 (2004)], the replacement of optically dense Y3Fe5O12 garnet by transparent Gd3Ga5O12 enables significant enhancement of light rejection within the stop band. Photonic crystals spectra experience blue shift in oblique incidence geometry thus demonstrating feasibility to use this effect for tunable magneto-optical filters.

  • 53.
    Khartsev, Sergiy
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT).
    Heteroepitaxial Bi3Fe5O12/La3Ga5O12 films for magneto-optical photonic crystals2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 14Article in journal (Refereed)
    Abstract [en]

    Epitaxial La3Ga5O12 (LGG) garnet films and Bi3Fe5O12/La3Ga5O12 (BIG/LGG) heteroepitaxial film structures have been synthesized on the Gd3Ga5O12(GGG,111) single crystal. LGG films were grown by pulsed laser deposition technique whereas rf-magnetron sputtering was used to grow BIG films. LGG has a lattice constant 12.768 A that is bigger than that in GGG (12.384 A) and closer to that in BIG (12.626 A). We demonstrate feasibility of integration lanthanum gallium garnet with a giant Faraday rotator Bi3Fe5O12 in magneto-optical photonic crystals. Heteroepitaxial Bi3Fe5O12(1.9 mu m)/La3Ga5O12(300 nm)/GGG(111) structures show Faraday rotation as high as 5.74 deg/mu m compared to 5.46 deg/mu m in BIG/GGG at lambda=655 nm. Fitting LGG reflectivity spectra to Fresnel formulas yields LGG refractive index n(o)=1.981 compared to 1.963 in GGG at 655 nm. Dispersion of LGG refraction index follows Sellmeier formula n(o)(2)=1+2.77/[1-(143 nm/lambda)(2)] in the range from 400 nm to 1000 nm.

  • 54.
    Khartsev, Sergiy
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Kim, Joo-Hyung
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT).
    Integration of colossal magnetoresistors with GaAs2005In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 284, no 02-jan, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Colossal magnetoresistive (CMR) La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) films have been grown by pulsed laser deposition technique on GaAs(001) substrates buffered with epitaxial MgO layer. X-ray diffraction revealed strong c-axis out-of-plane orientation and strong in-plane texture of CMR/MgO bilayers on GaAs single crystal. The maximum temperature coefficient of resistivity TCR = 9.0% K-1 at 223 K and 2.0% K-1 at 327 K. and the magnetoresistance Delta rho/rho similar to-7.95% kOe(-1) and -1.47% kOe(-1) have been achieved for LCMO/MgO/GaAs and LSMO/MgO/GaAs heteroepitaxial structures, respectively. Comparison with the test LCMO and LSMO films grown directly onto the bulk MgO(001) single cry tal demonstrates the identity of LSMO/MgO/GaAs and LSMO/MgO films properties whereas the LCMO films grown on MgO buffered GaAs show lower transition temperature T-c = 242 K compared to 253 K in LCMO/MgO.

  • 55. Koethe, T. C.
    et al.
    Hu, Z.
    Haverkort, M. W.
    Schuessler-Langeheine, C.
    Venturini, F.
    Brookes, N. B.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Reichelt, W.
    Hsieh, H. H.
    Lin, H. J.
    Chen, C. T.
    Tjeng, L. H.
    Transfer of spectral weight and symmetry across the metal-insulator transition in VO22006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 11Article in journal (Refereed)
    Abstract [en]

    We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

  • 56. Kollmus, H.
    et al.
    Kraemer, A.
    Bender, M.
    Bellachioma, M. C.
    Reich-Sprenger, H.
    Mahner, E.
    Hedlun, E.
    Westerberg, L.
    Malyshev, O. B.
    Leandersson, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Edqvist, E.
    Energy scaling of the ion-induced desorption yield for perpendicular collisions of Ar and U with stainless steel in the energy range of 5 and 100 MeV/u2009In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 27, no 2, p. 245-247Article in journal (Refereed)
    Abstract [en]

    For the GSI future project Facility for Antiproton and Ion Research a beam intensity of 10(12)U(28+)ions/s is planned to be extracted from the GSI heavy ion synchrotron SIS18. Measurements performed in 2001 showed that the beam lifetime of the ions in the synchrotron is decreasing with increasing number of injected particles due to vacuum instabilities caused by ion-induced desorption. The injection energy for the SIS18 is about 10 MeV/u and U28+ ions are accelerated to 200 MeV/u limited by the magnetic rigidity for the low charge state. The aim of this work was to measure the desorption yield as a function of the impact energy from injection to extraction of SIS18 at GSI. Low energy yields at 5.0, 9.7, and 17.7 MeV/u were measured at the Cyclotron of The Svedberg Laboratory in Uppsala. High energy yields at 40, 80, and 100 MeV/u were measured at SIS18 of GSI in a different setup. It was found that the desorption yield scales with the electronic energy loss (dE/dx)(el)(n), with n between 2 and 3, decreasing for increasing impact energy above the Bragg maximum.

  • 57. Kolokoltsev, O. V.
    et al.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Cortes Perez, Oliver
    Ordonez-Romero, C. L.
    Bragg diffraction of guided optical waves by spin dipole waves in a ferrimagnetic heterostructure2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 9Article in journal (Refereed)
    Abstract [en]

    The peculiarities of the Bragg diffraction of guided optical waves (GOWs) by spin-dipole waves (SDWs) in a ferrite heterostructure, based on Bi3Fe5O12 (BIG) thin film deposited on a standard YIG/GGG sample, is presented. It is shown that the efficiency of waveguide magneto-optic interaction between GOWs and SDWs in BIG/YIG/GGG can be 4-14 times large compared to the standard YIG/GGG waveguide, even in the case when the interacting waves are localized in YIG waveguide layer.

  • 58. Li, Zhuang-Zhi
    et al.
    Baca, Javier
    Yun, Sang Ho
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Wu, Judy
    Gold/boron core-shell nanocables synthesized from gold-boron eutectic droplets2008In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 19, no 5, p. 055606-Article in journal (Refereed)
    Abstract [en]

    Metal/semiconductor coreshell coaxial nanocables are promising building blocks for nanoelectronic devices while in situ growth of these nanocables remains challenging due to the distinctly different synthesis temperature ranges required for metals and semiconductors. To overcome this difficulty, we have developed a vaporliquidsolid and oxide-assisted bimodal competition growth strategy for in situ metal/semiconductor coreshell nanocable growth. Using this process, gold/boron coreshell nanocables were obtained. A coreshell Au-B/BOx eutectic droplet formed via hydrogen gas-assisted rapid cooling was found critical for initiation of the nanocable growth. In addition, the large difference in the boron nanowire growth rates in the vapor-liquid-solid and oxide-assisted mechanisms facilitates the layered growth in the nanocables. The compatibility of this method with the vapor-liquid-solid process applied widely for semiconductor nanowire growth allows in situ connection of metal/semiconductor nanocables with semiconductor nanowires.

  • 59. Maccaferri, Nicolo
    et al.
    Gonzalez-Diaz, Juan B.
    Bonetti, Stefano
    Berger, Andreas
    Kataja, Mikko
    van Dijken, Sebastiaan
    Nogues, Josep
    Bonanni, Valentina
    Pirzadeh, Zhaleh
    Dmitriev, Alexandre
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Vavassori, Paolo
    Polarizability and magnetoplasmonic properties of magnetic general nanoellipsoids2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 8, p. 9875-9889Article in journal (Refereed)
    Abstract [en]

    An approach to compute the polarizability tensor of magnetic nanoparticles having general ellipsoidal shape is presented. We find a surprisingly excellent quantitative agreement between calculated and experimental magneto-optical spectra measured in the polar Kerr configuration from nickel nanodisks of large size (exceeding 100 nm) with circular and elliptical shape. In spite of its approximations and simplicity, the formalism presented here captures the essential physics of the interplay between magneto-optical activity and the plasmonic resonance of the individual particle. The results highlight the key role of the dynamic depolarization effects to account for the magneto-optical properties of plasmonic nanostructures.

  • 60.
    Manuilov, Sergey A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Fors, Rickard
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Submicron Y3Fe5O12 Film Magnetostatic Wave Band Pass Filters2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 3Article in journal (Refereed)
    Abstract [en]

    Thin Y3Fe5O12 (YIG) films were pulsed laser deposited onto Gd3Ga5O12 (111) and (001) substrates. Processing conditions were optimized to obtain compressively strained films with a ferromagnetic resonance linewidth at 9 GHz as narrow as 0.9 Oe and high uniaxial magnetic anisotropy H-u=-880 Oe. Several designs of magnetostatic surface wave (MSSW) bandpass filters were fabricated and tested: 0.45 and 0.22 mu m thick YIG films lain on transducers alumina board and with microstripe transducers defined directly onto YIG film, with effective antenna areal sizes of 2 and 0.4 mm(2). The MSSW filter with 2 mm(2) antenna shows, at 7.5 GHz, insertion loss -9 dB and a resonant -3 dB bandwidth as narrow as 12.5 MHz.

  • 61.
    Manuilov, Sergey A
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy II2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 1, p. 013902-Article in journal (Refereed)
    Abstract [en]

    Recently we found epitaxial Fe-deficient yttrium iron garnet Y3Fe5-tO12-3t/2 (YIG) films pulsed laser deposited onto the (111) and (001) face of Gd3Ga5O12 single crystal experience, respectively, strong rhombohedral and tetragonal distortions and possess unusual magnetic anisotropy. Using the crystal field theory, we explained these anomalies and showed in YIG (111) films ferric ion vacancies preferentially occupy octahedral complexes, order themselves along the [111] growth direction, cause rhombohedral lattice distortions, generate strong uniaxial and significantly reduce cubic crystalline anisotropy, Manuilov et al., [J. Appl. Phys. 106, 123917 (2009)]. Oxygen vacancies govern electrical neutrality and in spite of high concentration (in access of 7 at. %) they are perfectly ordered that is indicated by narrow ferromagnetic resonance linewidth. The present paper aims to compare growth anisotropies induced in (111) and (001) epitaxial Fe-deficient YIG films. Ordering of vacancies appeared to be different in (111) and (001) oriented YIG films. In highly Fe-deficient YIG (001) we found much smaller imbalance in redistribution of vacancies between the octa-and tetrahedral magnetic sublattices. This feature together with a weaker crystal field in tetrahedral Fe3+-O2- complexes result in reduced growth induced magnetic anisotropy in (001) oriented tetragonal distorted YIGs compared to rhombohedral distorted YIG (111) films.

  • 62.
    Manuilov, Sergey A
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy I2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 12Article in journal (Refereed)
    Abstract [en]

    Recently we sintered by pulsed laser deposition (PLD) technique the epitaxial Fe-deficient yttrium iron garnet (YIG) films with ferromagnetic resonance (FMR) linewidth as narrow as 0.9 Oe, the uniaxial anisotropy as high as H-u=-880 Oe, and demonstrated them feasible for magnetostatic waves band pass filter application [Manuilov , J. Appl. Phys. 105, 033917 (2009)]. Here we explore the origin of unusually high noncubic magnetic anisotropy. Using the angular resolved FMR spectroscopy we found that in addition to strong uniaxial anisotropy, cubic magnetic anisotropy experienced almost fivefold reduction compared to standard YIG grown by liquid phase epitaxy. Molecular field theory was employed to calculate saturation magnetization 4 pi M-s, cubic magnetocrystalline K-1, and uniaxial anisotropy K-u in garnets with Fe vacancies. The modeling utilizes crystal field parameters that we revealed from earlier published experimental data on diamagnetic ion substituted Y3Fe5O12 and Fe-substituted isomorphous diamagnetic garnets. Consistent single ion anisotropy crystal field theory perfectly fits experimentally observed high saturation magnetization, reduction in cubic, and appearance of strong uniaxial anisotropy in PLD-grown Fe-deficient YIG films. The redistribution of Fe vacancies between different magnetic sublattices was quantified and confirmed that in YIG(111) films ferric ions preferentially leave vacant octahedrally coordinated sites. Simulation of growth induced anisotropy proves the ordering of Fe3+ vacancies within octahedral sites. At equal number of available ferric ions and vacancies, the latter populate the octahedrons with distortion axis perpendicular to the film surface with the probability equal to 0.67. Deformation blockage of octahedral complexes with distortion axes directed along the film surface reduces this probability down to 0.14.

  • 63. Markovich, V.
    et al.
    Jung, G.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Tsindlekht, M. I.
    Grishin, Alexander M.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Yuzhelevski, Ya
    Gorodetsky, G.
    Magnetic separation and inelastic tunneling in self-doped manganite films2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 4Article in journal (Refereed)
    Abstract [en]

    Magnetic and transport properties of 100 nm thick La0.9MnO3-delta self-doped manganite films have been investigated in the temperature range 5-300 K. The films exhibit a paramagnetic to ferromagnetic transition at T-C = 194 K. The temperature dependence of the resistivity shows a metal-insulator transition at 204 K and a strong resistivity increase below 160 K. The magnetoresistance was always negative and slightly bias dependent. Variations in resistivity with magnetic field and current are nonhysteretic, while the temperature dependence of the resistivity exhibits unusual inverse thermal hysteresis. The magnetic field independent inverse thermal hysteresis is strongly influenced by a thermal history of the sample. The data suggest that nonlinear low temperature transport is dominated by inelastic tunneling through intrinsic tunnel junctions formed by phase-separated ferromagnetic metallic domains and insulating anti ferromagnetic matrix.

  • 64. Masin, Martin
    et al.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Kudrnovsky, Josef
    Kotrla, Miroslav
    Drchal, Vaclav
    Critical Temperatures of Random Iron-Cobalt Overlayers on the fcc-Cu(001) Substrate2013In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 26, no 4, p. 809-812Article in journal (Refereed)
    Abstract [en]

    We have theoretically investigated thermodynamic properties of random iron-cobalt monolayer deposited on the fcc(001) face of copper. The effective two-dimensional Heisenberg Hamiltonian was constructed from first principles and used to estimate the Curie temperature. The random-phase approximation as well as Monte Carlo approach are used and critically compared. Calculations indicate a weak maximum of the Curie temperature for Fe-rich composition of the overlayer.

  • 65. Masin, Martin
    et al.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Kudrnovsky, Josef
    Kotrla, Miroslav
    Drchal, Vaclav
    First-principles study of thermodynamical properties of random magnetic overlayers on fcc-Cu(001) substrate2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 7, p. 075452-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical study of the thermodynamical properties of a fcc-Cu(001) substrate covered by an iron-cobalt monolayer as well as by an incomplete iron layer. The effective two-dimensional Heisenberg Hamiltonian is constructed from first principles and the properties of exchange interactions are investigated. The Curie temperatures are estimated using the Monte Carlo (MC) simulations and compared with a simplified approach using the random-phase approximation (RPA) in connection with the virtual-crystal approach (VCA) to treat randomness in exchange integrals. Calculations indicate a weak maximum of the Curie temperature as a function of composition of the iron-cobalt overlayer. While a good quantitative agreement between RPA-VCA and MC was found for the iron-cobalt monolayer, the RPA-VCA approach fails quantitatively for low coverage due to the magnetic percolation effect. We also present a study of the effect of alloy disorder on the shape of magnon spectra of random overlayers.

  • 66.
    Mohseni Armaki, Seyed Majid
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Spin valves and spin-torque oscillators with perpendicualr magnetic anisotropy2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Researches in spintronics, especially those remarkably classified in the current induced spin-transfer torque (STT) framework, circumvent challenges with different materials and geometries. Perpendicular magnetic anisotropy (PMA) materials are showing capability of holding promise to be employed in STT based spintronics elements, e.g. spin-torque oscillators (STOs), STT-magnetoresistive random access memories (STT-MRAMs) and current induced domain wall motion elements.

    This dissertation presents experimental investigations into developing sputter deposited Co/Ni multilayers (MLs) with PMA and employs these materials in nano-contact STOs (NC-STOs) based on giant magnetoresistance (GMR) effect and in pseudo-spin-valve (PSV) structures. The magnetostatic stray field coupling plays an important role in perpendicular PSVs. The temperature dependent coupling mechanism recommends that this coupling can be tailored, by i) the saturation magnetization and coercivity of the individual layers, ii) the coercivity difference in layers, and iii) the GMR spacer thickness, to get a well decoupled and distinguishable switching response. Moreover, this thesis focused on the implementation and detailed characterization of NC-STOs with strong PMA Co/Ni ML free layers and in-plane Co reference layers as orthogonal (Ortho) magnetic geometry in so-called Ortho-NC-STOs. The primary target of reaching record high STO frequencies, 12 GHz, at close to zero field, 0.02 Tesla, was achieved. However, in large external fields, >0.4 Tesla, an entirely new magnetodynamic object, a “magnetic droplet”, theoretically predicted in 1977, was discovered experimentally. Detailed experiments, combined with micromagnetic simulations, demonstrate the formation of a magnetic droplet with a partially reversed magnetization direction underneath the NC, and a zone of large amplitude precession in a region bounding the reversed magnetization. The magnetic droplet exhibits a very rich dynamics, including i) auto-modulation as a combine of droplet frequency with a slow time evolution (few GHz) of un-centering the droplet mode under the NC, ii) droplet breathing as reversible deformation of droplet mode with ½ droplet frequency. All observation of droplet opens a new mechanism of excitation for future fundamental studies as well as experiments especially for domain wall electronics and nano-scopic magnetism.

  • 67.
    Mohseni, Seyed Majid
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Dumas, R. K.
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sani, S. R.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Magnetostatically driven domain replication in Ni/Co perpendicular pseudo spins valves: the effect of ferromagnetic layer thickness and temperature cyclingManuscript (preprint) (Other academic)
  • 68.
    Mohseni, Seyed Majid
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Redjai Sani, Sohrab
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Persson, J.
    Nguyen, T. N. Anh
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Pogoryelov, Ye
    Muduli, P. K.
    Iacocca, E.
    Eklund, R. K.
    Dumas, R. K.
    Bonetti, Stefano
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Deac, A.
    Hoefer, M.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Spin Torque-Generated Magnetic Droplet Solitons2013In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 339, no 6125, p. 1295-1298Article in journal (Refereed)
    Abstract [en]

    Dissipative solitons have been reported in a wide range of nonlinear systems, but the observation of their magnetic analog has been experimentally challenging. Using spin transfer torque underneath a nanocontact on a magnetic thin film with perpendicular magnetic anisotropy (PMA), we have observed the generation of dissipative magnetic droplet solitons and report on their rich dynamical properties. Micromagnetic simulations identify a wide range of automodulation frequencies, including droplet oscillatory motion, droplet "spinning," and droplet "breather" states. The droplet can be controlled by using both current and magnetic fields and is expected to have applications in spintronics, magnonics, and PMA-based domain-wall devices.

  • 69.
    Mohseni, Seyed Majid
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sani, Sohrab R.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Persson, J.
    Nguyen, T. N. Anh
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Pogoryelov, Ye.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    High frequency operation of a spin-torque oscillator at low field2011In: Physica Status Solidi. Rapid Research Letters, ISSN 1862-6254, E-ISSN 1862-6270, Vol. 5, no 12, p. 432-434Article in journal (Refereed)
    Abstract [en]

    We demonstrate a nano-contact based spin-torque oscillator (STO) combining a high operating frequency with low field operation. The STO is based on an orthogonal spin-valve architecture with an in-plane Co polarizer and an out-of-plane Co/Ni multilayer free layer. High frequency operation at low external fields is achieved by tailoring the Co/Ni layer properties to increase the strength (H(k)) of the perpendicular magnetic anisotropy, while simultaneously reducing the saturation magnetization (M(s)). Our approach emphasizes the importance of mu(0)(H(k)-M(s)) in determining the operating frequency in this system, and suggests that yet higher frequencies should be attainable through further optimization. [GRAPHICS]

  • 70. Mohseni, Seyed Morteza
    et al.
    Hamdi, M.
    Yazdi, H. F.
    Banuazizi, S. Amir Hossein
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Redjai Sani, Sohrab
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mohseni, Seyed Majid
    Magnetic droplet soliton nucleation in oblique fields2018In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 97, no 184402Article in journal (Refereed)
    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.

  • 71. Muduli, P. K.
    et al.
    Heinonen, O. G.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Intrinsic frequency doubling in a magnetic tunnel junction-based spin torque oscillator2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 7, p. 076102-Article in journal (Refereed)
    Abstract [en]

    We show that the frequency of a magnetic tunnel junction (MTJ)-based spin torque oscillator (STO) can be doubled and the first harmonic entirely suppressed by orienting the free and fixed layer magnetizations in an antiparallel (AP) state. The angular dependence of the harmonics allows us to extract the free layer precession angle, which follows a parabolic decrease from a maximum of 20 degrees in the AP state to about 10 degrees at 25 degrees of misalignment. Frequency-doubling provides both a promising way for increasing the frequency of MTJ-STOs and a means for high-rate frequency shift keying using only a small magnetic field.

  • 72. Muduli, P. K.
    et al.
    Heinonen, O. G.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Temperature dependence of linewidth in nanocontact based spin torque oscillators: Effect of multiple oscillatory modes2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 17, p. 174408-Article in journal (Refereed)
    Abstract [en]

    We discuss the effect of mode transitions on the current (I) and temperature (T) dependent linewidth (Delta f) in nanocontact based spin torque oscillators (STOs). At constant I, Delta f exhibits an anomalous temperature dependence near the mode transitions; Delta f may either increase or decrease with T depending on the position w.r.t. the mode transition. We show that the behavior of Delta f as a function of I can be fitted by the single mode analytical theory of STOs, even though there are two modes present near the mode transition, if the nonlinear amplification is determined directly from the experiment. Using a recently developed theory of two coupled modes, we show that the linewidth near mode transition can be described by an "effective" single-oscillator theory with an enhanced nonlinear amplification that carries additional temperature dependence, which thus qualitatively explain the experimental results.

  • 73. Muduli, P. K.
    et al.
    Pogoryelov, Ye.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Zhou, Y.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mancoff, Fred
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Spin Torque Oscillators and RF Currents-Modulation, Locking, and Ringing2011In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 125, p. 147-154Article in journal (Refereed)
    Abstract [en]

    We study the interaction between a nano-contact spin torque oscillator (STO) and injected radio-frequency and microwave currents. Modulation of the STO signal is observed over a wide frequency range from 100 MHz to 3.2 GHz. The modulation side-bands agree well with macrospin simulations. When the injected microwave frequency approaches that of the STO, we observe injection locking, frequency pulling/pushing, and intermodulation peaks. While the intermodulation peaks are reasonably well reproduced by macrospin simulations, they do not follow the Adler's model. We argue that this discrepancy is due to intrinsic ringing effects stemming from the internal dynamics of the STO.

  • 74.
    Muduli, Pranaba
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Friedland, K. -J
    Herfort, J.
    Schoenherr, H. -P
    Ploog, K. H.
    Composition dependent properties of Fe3Si films grown on GaAs(113)A substrates2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 7, p. 07B104-Article in journal (Refereed)
    Abstract [en]

    Structural, electrical, and magnetic properties of Fe3Si/GaAs(113)A hybrid structures are studied, dependent on the layer composition varying from 15 to 26 at. % Si. The presence of superlattice reflections in x-ray diffraction and lower resistivity confirms the long-range atomic ordering in the stoichiometric Fe3Si films, reflecting the D0(3) crystal structure. The observed atomic ordering is also found to influence the sign and magnitude of the antisymmetric component of the planar Hall effect observed in this orientation. However a finite disorder is observed even in nearly stoichiometric samples.

  • 75.
    Muduli, Pranaba K.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Herfort, J.
    Schoenherr, H. -P
    Ploog, K. H.
    Spin wave excitations in Fe films grown on GaAs(113)A substrates2008In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 320, no 21, p. 2835-2838Article in journal (Refereed)
    Abstract [en]

    The spin wave excitation and its size effect has been studied in Al- capped Fe. lms grown on lowsymmetry GaAs( 113) A substrates. The temperature dependence of saturation magnetization follows an effective Bloch's law as long as magnetization remains larger than about 70% of its saturation value. A signi. cant increase of the spin wave parameter B is found in Al- capped ultrathin Fe. lms grown on GaAs( 113) A compared to bulk Fe, Fe. lms on GaAs( 0 01) and other systems. This is explained as a result of the reduction in uniaxial magnetic anisotropy observed in this orientation for the same thickness range. However, this observed uniaxial magnetic anisotropy is found to be a likely reason for stabilizing the ferromagnetism.

  • 76.
    Muduli, Pranaba
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Pogoryelov, Ye.
    Mancoff, F.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Modulation of Individual and Mutually Synchronized Nanocontact-Based Spin Torque Oscillators2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 6, p. 1575-1579Article in journal (Refereed)
    Abstract [en]

    We study current modulation of spin torque oscillators (STOs) based on single and double nano-contacts. For single nano-contact devices, we show modulation for a carrier frequency of 19-40 GHz and modulation frequencies from 50 MHz to 1 GHz. We show that the behavior of modulation and the asymmetry in the power of the modulation sidebands can be very well modeled, and predicted, using nonlinear frequency and amplitude modulation (NFAM) calculations based on the free-running STO parameters. Modulation of synchronized double nano-contact STOs is equally well modeled by NFAM theory and demonstrates the feasibility of communication applications based on arrays of synchronized STOs.

  • 77.
    Muduli, Pranaba
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Pogoryelov, Yevgen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Consolo, Giancarlo
    University of Messina.
    Mancoff, Fred
    Everspin Technologies Inc.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Modulation of single and double spin torque oscillators2010In: INTERNATIONAL CONFERENCE ON MAGNETIC MATERIALS (ICMM-2010), 2010, p. 318-321Conference paper (Refereed)
    Abstract [en]

    We discuss modulation of metallic spin torque oscillators (STOs) based on single and double nano-contacts. The modulation behavior of both types of devices is characterized by equally spaced multiple sidebands, which can be ascribed mostly to a frequency modulation phenomenon. However, quantitative examination reveals that amplitude modulation is also present in both types of devices. We also show the feasibility of modulating the synchronized state of a double nano-contact STO. The synchronized state can be treated as a single oscillator, which is a very promising feature for future applications of STO arrays.

  • 78.
    Najmoddin, Najmeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Beitollahi, Ali
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ansari, Narges
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Devlin, Eamonn
    Mohseni, Seyed Majid
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Rezaie, Hamidreza
    Niarchos, Dimitris
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Effect of nanoconfinement on the formation, structural transition and magnetic behavior of mesoporous copper ferrite2014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 598, p. 191-197Article in journal (Refereed)
    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.

  • 79. Nguyen, T. N. Anh
    et al.
    Fang, Yeyu
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Fallahi, Vahid
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Benatmane, Nadjib
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mohseni Armaki, Seyed Majid
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Dumas, R. K.
    Åkerman, Johan
    [Co/Pd]-NiFe exchange springs with tunable magnetization tilt angle2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 17, p. 172502-Article in journal (Refereed)
    Abstract [en]

    We investigate exchange coupled [Co/Pd](5)-NiFe thin films. Due to competition between the in-plane shape anisotropy of the NiFe and strong perpendicular magnetic anisotropy of the [Co/Pd](5) multilayer, unique magnetic configurations are achievable. In particular, we explore the out-of-plane magnetization tilt angle of the NiFe layer. Experimental results, based on conventional magnetometry, ferromagnetic resonance, and magnetic force microscopy, agree well with one-dimensional micromagnetic simulations. We find that the tilt angle is highly tunable [0 degrees-60 degrees] over a small range of NiFe thicknesses (4.8-8nm). Potential applications for high power, zero-field operation spin torque oscillators are discussed.

  • 80.
    Nguyen, Thi Ngooc Ahn
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Benatmane, Nadjib
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Fallahi, Vahid
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Fang, Yeyu
    Mohseni, Seyed Majid
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Dumas, R. K.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    [Co/Pd](4)-Co-Pd-NiFe spring magnets with highly tunable and uniform magnetization tilt angles2012In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 324, no 22, p. 3929-3932Article in journal (Refereed)
    Abstract [en]

    By varying the Pd thickness (t(Pd)) from 0 to 8 nm in [Co/Pd](4)/Co/Pd(t(Pd))/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd](4)/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20 degrees to 80 degrees, and(iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd](4)/Co/Pd(t(Pd))/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom.

  • 81. Nilson, K.
    et al.
    Åhlund, J.
    Shariati, M. -N
    Schiessling, J.
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Brena, B.
    Göthelid, E.
    Hennies, F.
    Huismans, Y.
    Evangelista, F.
    Rudolf, P.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mårtensson, N.
    Puglia, C.
    Potassium-intercalated H2Pc films: Alkali-induced electronic and geometrical modifications2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 4, p. 044708-Article in journal (Refereed)
    Abstract [en]

    X-ray spectroscopy studies of potassium intercalated metal-free phthalocyanine multilayers adsorbed on Al(110) have been undertaken. Photoelectron spectroscopy measurements show the presence of several charge states of the molecules upon K intercalation, due to a charge transfer from the alkali. In addition, the comparison of valence band photoemission spectra with the density functional theory calculations of the density of states of the H2Pc- anion indicates a filling of the formerly lowest unoccupied molecular orbital by charge transfer from the alkali. This is further confirmed by x-ray absorption spectroscopy (XAS) studies, which show a decreased density of unoccupied states. XAS measurements in different experimental geometries reveal that the molecules in the pristine film are standing upright on the surface or are only slightly tilted away from the surface normal but upon K intercalation, the molecular orientation is changed in that the tilt angle of the molecules increases.

  • 82. Nylen, Johanna
    et al.
    Lidin, Sven
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Iversen, Bo Brummerstedt
    Liu, Hongxue
    Newman, Nate
    Haussermann, Ulrich
    Low-temperature structural transitions in the phonon-glass thermoelectric material beta-Zn4Sb3: Ordering of Zn interstitials and defects2007In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 19, no 4, p. 834-838Article in journal (Refereed)
    Abstract [en]

    The low-temperature phase transitions of thermoelectric Zn4Sb3 have been characterized using single-crystal X-ray diffraction, electrical resistance, and thermal conductivity measurements. Room-temperature stable, disordered beta-Zn4Sb3 undergoes a phase transition at 254 K to ordered alpha-Zn4Sb3, which has an ideal composition Zn13Sb10. Below 235 K, a second low-temperature phase (alpha'-Zn4Sb3) can be detected. The sequence of phase transitions beta-alpha-alpha' is reversible. The alpha-alpha' transformation originates from a slight Zn deficiency with respect to Zn13Sb10. The actual composition of Zn4Sb3 is Zn13-delta Sb10.

  • 83. Nylen, Johanna
    et al.
    Lidin, Sven
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Liu, Hongxue
    Newman, Nate
    Haussermann, Ulrich
    Effect of metal doping on the low-temperature structural behavior of thermo electric beta-Zn4Sb32007In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 180, no 9, p. 2603-2615Article in journal (Refereed)
    Abstract [en]

    The low-temperature structural phase transitions of Bi, Pb, In and Sn-doped samples of thermoelectric Zn4Sb3 have been characterized on crystals grown from molten metal fluxes, using electrical resistance and single crystal X-ray diffraction measurements. Room temperature stable, disordered, beta-Zn4Sb3 undergoes two phase transitions at 254 and 235 K to the consecutively higher ordered phases a and alpha', respectively. The ideal crystallographic composition of alpha-Zn4Sb3 is Zn13Sb10. The alpha-alpha' transformation is triggered by a slight and homogenous Zn deficiency with respect to this composition and introduces a compositional modulation in the alpha-Zn4Sb3 structure. When preparing beta-Zn4Sb3 in the presence of metals with low melting points (Bi, Sn, In, Pb) the additional metal atoms are unavoidably incorporated in small concentrations (0.04-1.3 at%.) and act as dopants. This incorporation alters the subtle balance between Zn disorder and Zn deficiency in Zn4Sb3 and has dramatic consequences for its low-temperature structural behavior. From molten metal flux synthesis it is possible to obtain (doped) Zn4Sb3 samples which (1) only display a P-a transition, (2) only display a beta-alpha' transition, or (3) do not display any low-temperature phase transition at all. Case (2) provided diffraction data with a sufficient quality to obtain a structural model for highly complex, compositionally modulated, alpha'-Zn4Sb3. The crystallographic composition of this phase is Zn84Sb65.

  • 84. Ofer, O.
    et al.
    Baglo, J. C.
    Hossain, M. D.
    Kiefl, R. F.
    Hardy, W. N.
    Thaler, A.
    Kim, H.
    Tanatar, M. A.
    Canfield, P. C.
    Prozorov, R.
    Luke, G. M.
    Morenzoni, E.
    Saadaoui, H.
    Suter, A.
    Prokscha, T.
    Wojek, Bastian M.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Salman, Z.
    Absolute value and temperature dependence of the magnetic penetration depth in Ba(Co 0.074Fe 0.926) 2As 22012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 6, p. 060506-Article in journal (Refereed)
    Abstract [en]

    The absolute value and temperature dependence of the in-plane magnetic penetration depth lambda have been measured on a single crystal of Ba(Co0.074Fe0.926)(2)As-2 using low-energy muon-spin rotation and microwave cavity perturbation. The magnetic field profiles in the Meissner state are consistent with a local London model beyond a depth of 15 nm. We determine the gap symmetry through measurements of the temperature dependence of the superfluid density which follows a two-gap s-wave model over the entire temperature range below T-c. While the intermediate to high temperature data is well fit by an energy gap model in the BCS-like (weak-coupling) limit, a second smaller gap becomes apparent at low temperatures.

  • 85. Panaccione, G.
    et al.
    Altarelli, M.
    Fondacaro, A.
    Georges, A.
    Huotari, S.
    Lacovig, P.
    Lichtenstein, A.
    Metcalf, P.
    Monaco, G.
    Offi, F.
    Paolasini, L.
    Poteryaev, A.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Sacchi, M.
    Coherent peaks and minimal probing depth in photoemission spectroscopy of Mott-Hubbard systems2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 11Article in journal (Refereed)
    Abstract [en]

    We have measured hard x-ray photoemission spectra of pure vanadium sesquioxide (V2O3) across its metal-insulator transition. We show that, in the metallic phase, a clear correlation exists between the shakedown satellites observed in the vanadium 2p and 3p core-level spectra and the coherent peak measured at the Fermi level. Comparing experimental results and dynamical mean-field theory calculations, we estimate the Hubbard energy U in V2O3 (4.20 +/- 0.05 eV). From our bulk-sensitive photoemission spectra we infer the existence of a critical probing depth for investigating electronic properties in strongly correlated solids.

  • 86. Pikulev, V. B.
    et al.
    Kuznetsov, S. N.
    Kuznetsov, Alexandr
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Saren, A. A.
    Gurtov, V. A.
    Singlet oxygen inhibits nonradiative defects in porous silicon2009In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 206, no 6, p. 1268-1272Article in journal (Refereed)
    Abstract [en]

    Experimental evidences are presented for the first time that singlet oxygen generated ex situ acts as an inhibitor of nonradiative recombination in porous silicon (PSi). This effect is observed on a pristine PSi as well as on degraded porous layers quenched by ozone adsorption. A photoluminescence (PL) enhancement produced by singlet oxygen is accompanied with only slight oxidation of a PSi. We assume that the observed effect on PL efficiency is due to gentle selective oxidation of single defects on silicon nanocrystal surface.

  • 87. Pisarev, A.
    et al.
    Tanabe, T.
    Emmoth, Birger
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Trifonov, N.
    Rusinov, A.
    Stepanov, S.
    Gasparyan, Yu.
    Spitsyn, A.
    Khripunov, B.
    Deuterium accumulation in carbon materials at high fluence2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 390-91, p. 677-680Article in journal (Refereed)
    Abstract [en]

    D retention in fine grain graphite MPG-8 and carbon fiber composite NB31 after exposure to plasma was investigated by means of thermal desorption spectroscopy. It was observed, that deuterium accumulation in the two materials was similar in the region of the fluence of 10(22)-4 x 10(24) D+/m(2), though NB31 retains about twice as much. The retention in MPG-8 reveals no saturation at high fluences and no flux dependence in the range of (0.5-3.5) x 10(20) D+/m(2) s. The difference between polished and unpolished samples, as well as between samples kept in air for various times after irradiation was within the experimental uncertainty.

  • 88. Pogoryelov, Y.
    et al.
    Muduli, P. K.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Combined wide-narrow double modulation of spin-torque oscillators for improved linewidth during communication2012In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 48, no 11, p. 4077-4080Article in journal (Refereed)
    Abstract [en]

    Spin-torque oscillators (STOs) offer the advantage of high modulation rates. However the existence of regions with high-frequency nonlinearity, accompanied by increased signal linewidth, limits both the usable STO frequency range and the minimum frequency of modulation. On the other hand, use of a large modulation frequency increases the frequency modulation (FM) bandwidth. In order to overcome these problems, we propose to simultaneously modulate the STO with two signals having different frequencies. We use a high-frequency, wide (f W = 500 MHz), modulation signal to improve the STO linewidth. At the same time we use a low-frequency, narrow (f N = 40 MHz), modulation signal to show successful narrow bandwidth modulation of the improved STO signal. The proposed method of combined wide-narrow double modulation can significantly improve the usable operating frequency range of the STOs for communication applications.

  • 89.
    Pogoryelov, Yevgen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Manifestation of Spin-Hall Effect in Multilayered M/N/M Film Structures2010In: INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) / [ed] Goll, G; Lohneysen, HV; Loidl, A; Pruschke, T; Richter, M; Schultz, L; Surgers, C; Wosnitza, J, BRISTOL: IOP PUBLISHING LTD , 2010, Vol. 200, p. UNSP 052023-Conference paper (Refereed)
    Abstract [en]

    In the present work spin-Hall effect was for the first time experimentally utilized at room temperatures for studies of interlayer exchange coupling in ultrathin (3-40 angstrom) M/N/M film structures at zero applied external magnetic field. Application of special technique allowed to discover the possible influence of external magnetic field on the behavior of exchange coupling oscillations. Obtained results are well explained if to take into account in the RKKY model the probable influence of magnetic field on the spin-dependent reflection coefficients of spin-polarized conduction electrons from magnetic interfaces.

  • 90. Qi, B.
    et al.
    Agnarsson, B.
    Olafsson, S.
    Gislason, H. P.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Room temperature deposition of self-assembled Al nanoclusters on stepped sapphire (0001) surface and subsequent nitridation2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 1, p. 64-73Article in journal (Refereed)
    Abstract [en]

    Self-assembled growth and nitridation of ultrathin Al nanoclusters on a stepped sapphire (0001) surface were studied by high-resolution X-ray photoemission spectroscopy, atomic force microscopy and low-energy electron diffraction (LEED). Upon room temperature deposition, in the coverage range of similar to 0.79 to 2.3 monolayer (ML), Al nanoclusters were uniformly nucleated over the entire surface of defect-free atomically smooth terraces as well as step edges. Subsequent nitridation at elevated temperatures by ammonia did not alter the morphology of the nanoclusters. The global morphology of the stepped sapphire (0001) surface such as terrace width, step height and facet orientation had no obvious influence on the nucleation morphology of the nanoclusters in the given Al coverage range. However, local structural defects at the joints of short facets and step edges played a noticeable role on the local morphology of the nanoclusters and subsequently the nitridation chemistry. The Al nanoclusters were uniformly nitridated from surface and downwards through the 3D structures. The LEED pattern indicated a certain degree of crystallinity on the nitridated surface at a nominal Al coverage less than 2 ML, whereas at 2.3 ML Al coverage, the nitridated surface became amorphous. Thus there is a critical coverage for good surface order.

  • 91. Qi, B.
    et al.
    Olafsson, S.
    Zakharov, A. A.
    Agnarsson, B.
    Gislason, H. P.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    A micro-spectroscopy study on the influence of chemical residues from nanofabrication on the nitridation chemistry of Al nanopatterns2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 10, p. 4497-4506Article in journal (Refereed)
    Abstract [en]

    We applied spatially resolved photoelectron spectroscopy implemented with an X-ray photoemission electron microscopy (XPEEM) using soft X-ray synchrotron radiation to identify the compositional and morphological inhomogeneities of a SiO2/Si substrate surface nanopatterned with Al before and after nitridation. The nanofabrication was conducted by a polymethylmethacrylate (PMMA)-based e-beam lithography and a fluorine-based reactive ion etching (RIE), followed by Al metalization and acetone lift-off. Three types of chemical residues were identified before nitridation: (1) fluorocarbons produced and accumulated mainly during RIE process on the sidewalls of the nanopatterns; (2) a thick Al-bearing PMMA layer and/or (3) a thin PMMA residue layer owing to unsuccessful or partial lift-off of the e-beam unexposed PMMA between the nanopatterns. The fluorocarbons actively influenced the surface chemical composition of the nanopatterns by forming Al-F compounds. After nitridation, in the PMMA residue-free area, the Al-F compounds on the sidewalls were decomposed and transformed to AIN. The PMMA residues between the nanopatterns had no obvious influence on the surface chemical composition and nitridation properties of the Al nanopatterns. They were only partially decomposed by the nitridation. The regional surface morphology of the nanopatterns revealed by the secondary electron XPEEM was consistent with the scanning electron microscopy results.

  • 92.
    Rapp, Östen
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Electronic properties of alloys2008In: Basics of thermodynamics and phase transitions in complex metallic alloys / [ed] E. Belin-Ferré, New Jersey: World Scientific, 2008, p. 259-318Chapter in book (Other academic)
    Abstract [en]

    Electronic proprties of alloys consisting of metals are reviewed starting from the level of an undergraduate curriculum in solid state physics. These alloys occur in three different forms of solid matter, viz. crystalline alloys, amorphous alloys, and quasicrystals. A selection of electronic properties of these materials will be discussed, including examples from conduction in good metals to electron transport  in insulators. The presentation is intended as a background to complex metallic alloys, the main theme of the School.

  • 93.
    Rapp, Östen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Feuerbacher, M.
    Anomalous transport in rhombohedral MgM2Al32009In: 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2 / [ed] Kes P; Jochemsen R, 2009, Vol. 150Conference paper (Refereed)
    Abstract [en]

    The cubic (beta) and the rhombohedral- (beta') phases of Mg2Al3 are complex metallic alloys of related structure and more then 800 atoms in their unit cells. The electronic transport properties of these phases are remarkably different. We report and discuss some aspects of the magnetoresistance of these phases.

  • 94.
    Rapp, Östen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Karkin, A. A.
    Goshchitskii, B. N.
    Voronin, V. I.
    Srinivas, V.
    Poon, S. J.
    Electronic and atomic disorder in icosahedral AlPdRe2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 11, p. 114120-Article in journal (Refereed)
    Abstract [en]

    Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out.

  • 95.
    Rapp, Östen.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Srinivas, V.
    Poon, S. J.
    Critical exponents at the metal-insulator transition in AlPdRe quasicrystals2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 1Article in journal (Refereed)
    Abstract [en]

    Insulating icosahedral AlPdRe with resistance ratios R[=rho(4.2 K)/rho(295 K)] from 40 to 220 has been studied by magnetoresistance and conductivity measurements. Consistent results for the localization length xi and the characteristic temperature T-o were determined. (R-R-c) increases from the metal insulator transition (MIT) into the insulator as the inverse of the shrinking volume of the electron wave functions similar toxi(-3). Localization is driven by disorder. Evidence is discussed that the MITs in i-AlPdRe and doped semiconductors belong to the same universality class.

  • 96.
    Rapp, Östen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Srinivas, V.
    Poon, S. J.
    Recent results at the metal-insulator transition of icosahedral AIPdRe2006In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 86, no 05-mar, p. 655-661Article in journal (Refereed)
    Abstract [en]

    The metal-insulator transition, MIT, in icosahedral AlPdRe has been studied from measurements of magnetoresistance and conductivity. Results for the localisation length xi, the characteristic hopping temperature To and their relations at the MIT are discussed. The results indicate important similarities between i-AlPdRe and doped semiconductors.

  • 97. Razzoli, E.
    et al.
    Sassa, Y.
    Drachuck, G.
    Mansson, M.
    Keren, A.
    Shay, M.
    Berntsen, Magnus H.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Tjernberg, Oscar
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Radovic, M.
    Chang, J.
    Pailhes, S.
    Momono, N.
    Oda, M.
    Ido, M.
    Lipscombe, O. J.
    Hayden, S. M.
    Patthey, L.
    Mesot, J.
    Shi, M.
    The Fermi surface and band folding in La2-xSrxCuO4, probed by angle-resolved photoemission2010In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 12, p. 125003-Article in journal (Refereed)
    Abstract [en]

    A systematic angle-resolved photoemission study of the electronic structure of La2-xSrxCuO4 in a wide doping range is presented in this paper. In addition to the main energy band, we observed a weaker additional band, the (pi, pi) folded band, which shows unusual doping dependence. The appearance of the folded band suggests that a Fermi surface reconstruction is doping dependent and could already occur at zero magnetic field.

  • 98.
    Redjai Sani, Sohrab
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Fabrication and Characterization of Nanocontact Spin-Torque Oscillators2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The manufacturing of nanocontact-based spin-torque oscillators (NC-STOs)has opened the door for spintronic devices to play a part as active microwaveelements. The NC-STO has the capability of converting a direct current intoa microwave signal, and vice versa, by utilizing the spin transfer torque (STT)in ferromagnetic multilayer systems. However, the high-frequency operation ofNC-STOs typically requires high magnetic fields and the microwave power theygenerate is rather limited. As a result, NC-STOs are not yet commercially used,and they require improvements in both material systems and device geometriesbefore they can find actual use in microwave applications.

    In order to improve and advance this technology, NC-STOs are requiredwith both different nanocontact (NC) sizes and geometries, and using differ- ent stacks of magnetic materials. This dissertation presents experimental in- vestigations into the manufacturing of such devices using different fabrication techniques and a number of different magnetic material stacks. Currently, the fabrication of NC-STOs is limited to advanced laboratories, because NC fabri- cation requires high-resolution lithography tools. In the present work, we have developed an alternative method of fabrication, which does not require such tools and has the capability of fabricating NC-STOs having one to hundreds of NCs in a variety of sizes, possibly  down to 20 nm. Devices fabricated with this method have shown mutual synchronization of three parallel-connected NCs, and pairwise synchronization in devices with four and five NCs.

    Furthermore, the present work demonstrates low-field operation (down to0.02 Tesla) of NC-STOs at a record high frequency of 12 GHz. This wasachieved by implementing multilayers with a perpendicular magnetic anisotropy(PMA) material in the free layer of the NC-STO. In addition, the fabricateddevices revealed an unexpected dynamic regime under large external appliedfield (above 0.4 Tesla). The new dynamic regime was found to be due to anentirely novel nanomagnetic dynamic object â a so-called magnetic droplet soliton,predicted theoretically in 1977 but not experimentally observed until now.Detailed experiments and micromagnetic simulations show that the droplet hasvery rich dynamics.

    Finally,  spin-torque-induced  transverse spin wave instabilities have beenstudied.  A NC-STO with  a material stack consisting of a single ferromag- netic metal sandwiched between two non-ferromagnetic metals was fabricated. Prior to this work, evidence of spin wave instabilities was reported as resis- tance switching in nanopillar- and mechanical point contact based STOs. In the present  work, the fabricated NC-STOs showed actual microwave  signals up to 3 GHz under zero applied field with strong current hysteresis. All  the fabricated NC-STOs open up new means of studying STT in different environ- ments, in order to resolve their current drawbacks for industrial applications.

  • 99.
    Revenikiotis, Sackis (Athanasios)
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    Optimization of STM-tip preparation methods2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Scanning Tunneling Microscope (STM) was invented by Gerd Binnig and Heinrich Rohrer and gave them the Nobel Prize in Physics 1986. STM can give us atomic resolution of a surface by applying a voltage between a very sharp tip (STM-tip) and the surface of a material that we want to examine. The STM-tip is moving over the surface and a computer is collecting the tunnel current in every single point to create a digital image.

    This diploma work is focused on the preparation of the STM-tip. The preparation method that is used is electrochemical etching of a tungsten wire. The sharper the STM-tip is the better resolution in the STM images we can get. With the purpose to get as sharp tip as possible and with a well-defined geometry, we prepared several tips by systematically varying the etching parameters such as voltage, current, concentration and wire length. A new method has been tested to minimize the oxidation on the surface and finally the tips were characterized with scanning electron microscope (SEM).

  • 100. Rihtnesberg, D. B.
    et al.
    Almqvist, S.
    Wang, Q.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Yang, Xuran
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Besharat, Zahra
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Material Physics, MF (Closed 20120101).
    ZnO nanorods/nanoflowers and their applications2011In: Proc. - Int. NanoElectronics Conf., INEC, 2011Conference paper (Refereed)
    Abstract [en]

    Single-crystalline zinc oxide (ZnO) nanorods (NRs) have been synthesized through a chemical bath deposition method. Their diameter is about 80 nm, and their length range from 1 μm to 7 μm can be controlled by growth time. Formation of nanoflower arrays composed of nanorods has been also achieved utilizing a standard micro-fabrication technique. Two types of ZnO nanorods devices are detailed to demonstrate their optoelectronic applications.

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