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  • 1.
    Andersson, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    A quality process for assessing mathematics in a study programme2018In: Proceedings från 6:e utvecklingskonferensen för Sveriges ingenjörsutbildningar / [ed] Lena Petersson, Kristina Edström, Oskar Gedda, Fredrik Georgsson, Liselott Lycke och Marie Arehag, 2018Conference paper (Refereed)
    Abstract [en]

    We present two methodologies to assess the use of mathematics in a study programme. Firstly, we use a relatively simple methodology to assess how students show their ability to use mathematics in their degree project reports. Secondly, we present a methodology to assess how mathematics is used during a study programme. We have applied the first methodology on the mathematics content in 114 randomly chosen bachelor degree reports from 6 different study programmes within the fields of electrical engineering and computer engineering at KTH. For the 3-year bachelor degree programmes in computer engineering, we find clear deficits in the way students use mathematics in their bachelor degree reports as compared to the other programmes in our study. Through the second methodology, we were able to relate the deficits in the bachelor degree reports to a programme structure where skills in mathematics have not been sufficiently demanded in the engineering courses of the programme. 

  • 2. Bergman, Anders
    et al.
    Hellsvik, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Bessarab, Pavel F.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Univ Iceland, Iceland.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 36872Article in journal (Refereed)
    Abstract [en]

    Recent experimental data demonstrate emerging magnetic order in platinum atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy-colossal magnetic anisotropy (CMA)-was earlier predicted to exist in atomically thin platinum nanowires. Using spin dynamics simulations based on first-principles calculations, we here explore the spin dynamics of atomically thin platinum wires to reveal the spin relaxation signature of colossal magnetic anisotropy, comparing it with other types of anisotropy such as uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin relaxation process distinctly and, most importantly, causes a large speed-up of the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic behavior of the nanowire exhibiting CMA should be possible to identify experimentally at the nanosecond time scale for temperatures below 5 K. This time-scale is accessible in e.g., soft x-ray free electron laser experiments.

  • 3.
    Bergman, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Skubic, B
    Hellsvik, J
    Nordstrom, L
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, O
    Ultrafast switching in a synthetic antiferromagnetic magnetic random-access memory device2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 22Article in journal (Refereed)
    Abstract [en]

    The dynamics of a synthetic antiferromagnet (a metallic trilayer) have been explored and are shown to exhibit ultrafast switching on a time scale of tens of ps. This conclusion is based on first-principles, atomistic spin dynamics simulations. The simulations are performed at finite temperature, as well as at T = 0 K (the macrospin limit), and we observe a marked temperature dependence of the switching phenomenon. It is shown that, to reach very high switching speeds, it is important that the two ferromagnetic components of the synthetic antiferromagnet have oppositely directed external fields to one another. Then a complex collaboration between precession switching of an internal exchange field and the damping switching of the external field occurs, which considerably accelerates the magnetization dynamics. We discuss a possible application of this fast switching as a magnetic random access memory device, which has as a key component intrinsic antiferromagnetic couplings and an applied Oersted field.

  • 4. Bessarab, Pavel F.
    et al.
    Mueller, Gideon P.
    Lobanov, Igor S.
    Rybakov, Filipp N.
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Kiselev, Nikolai S.
    Jonsson, Hannes
    Uzdin, Valery M.
    Blugel, Stefan
    Bergqvist, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lifetime of racetrack skyrmions2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 3433Article in journal (Refereed)
    Abstract [en]

    The skyrmion racetrack is a promising concept for future information technology. There, binary bits are carried by nanoscale spin swirls-skyrmions-driven along magnetic strips. Stability of the skyrmions is a critical issue for realising this technology. Here we demonstrate that the racetrack skyrmion lifetime can be calculated from first principles as a function of temperature, magnetic field and track width. Our method combines harmonic transition state theory extended to include Goldstone modes, with an atomistic spin Hamiltonian parametrized from density functional theory calculations. We demonstrate that two annihilation mechanisms contribute to the skyrmion stability: At low external magnetic field, escape through the track boundary prevails, but a crossover field exists, above which the collapse in the interior becomes dominant. Considering a Pd/Fe bilayer on an Ir(111) substrate as a well-established model system, the calculated skyrmion lifetime is found to be consistent with reported experimental measurements. Our simulations also show that the Arrhenius pre-exponential factor of escape depends only weakly on the external magnetic field, whereas the pre-exponential factor for collapse is strongly field dependent. Our results open the door for predictive simulations, free from empirical parameters, to aid the design of skyrmion-based information technology.

  • 5.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Boman, Magnus
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 6.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Stochastic Thermodynamics of Oscillators' Networks2018In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 20, no 12, article id 992Article in journal (Refereed)
    Abstract [en]

    We apply the stochastic thermodynamics formalism to describe the dynamics of systems of complex Langevin and Fokker-Planck equations. We provide in particular a simple and general recipe to calculate thermodynamical currents, dissipated and propagating heat for networks of nonlinear oscillators. By using the Hodge decomposition of thermodynamical forces and fluxes, we derive a formula for entropy production that generalises the notion of non-potential forces and makes transparent the breaking of detailed balance and of time reversal symmetry for states arbitrarily far from equilibrium. Our formalism is then applied to describe the off-equilibrium thermodynamics of a few examples, notably a continuum ferromagnet, a network of classical spin-oscillators and the Frenkel-Kontorova model of nano friction.

  • 7.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Iubini, Stefano
    Lepri, Stefano
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Fransson, Jonas
    Coherent energy transport in classical nonlinear oscillators: An analogy with the Josephson effect2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 4, article id 040102Article in journal (Refereed)
    Abstract [en]

    By means of a simple theoretical model and numerical simulations, we demonstrate the presence of persistent energy currents in a lattice of classical nonlinear oscillators with uniform temperature and chemical potential. In analogy with the well-known Josephson effect, the currents are proportional to the sine of the phase differences between the oscillators. Our results elucidate general aspects of nonequilibrium thermodynamics and point towards a way to practically control transport phenomena in a large class of systems. We apply the model to describe the phase-controlled spin-wave current in a bilayer nanopillar.

  • 8.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala University, Sweden.
    Iubini, Stefano
    Lepri, Stefano
    Chico, Jonathan
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Uppsala University, Sweden.
    Fransson, Jonas
    Energy and magnetization transport in nonequilibrium macrospin systems2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, no 1, article id 012116Article in journal (Refereed)
    Abstract [en]

    We investigate numerically the magnetization dynamics of an array of nanodisks interacting through the magnetodipolar coupling. In the presence of a temperature gradient, the chain reaches a nonequilibrium steady state where energy and magnetization currents propagate. This effect can be described as the flow of energy and particle currents in an off-equilibrium discrete nonlinear Schrodinger (DNLS) equation. This model makes transparent the transport properties of the system and allows for a precise definition of temperature and chemical potential for a precessing spin. The present study proposes a setup for the spin-Seebeck effect, and shows that its qualitative features can be captured by a general oscillator-chain model.

  • 9.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lepri, Stefano
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Thermomagnonic diode: Rectification of energy and magnetization currents2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 5, p. 054428-Article in journal (Refereed)
    Abstract [en]

    We investigate the dynamics of two coupled macrospins connected to thermal baths at different temperatures. The system behaves like a diode which allows the propagation of energy and magnetization currents in one direction only. This effect is described by a simple model of two coupled nonlinear oscillators interacting with two independent reservoirs. It is shown that the rectification phenomenon can be interpreted as a a stochastic phase synchronization of the two spin oscillators. A brief comparison with realistic micromagnetic simulations is presented. This new effect yields promising opportunities in spin caloritronics and nanophononic devices.

  • 10. Borlenghi, Simone
    et al.
    Mahani, M. R.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fangohr, Hans
    Franchin, M.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Fransson, Jonas
    Micromagnetic simulations of spin-torque driven magnetization dynamics with spatially resolved spin transport and magnetization texture2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094428Article in journal (Refereed)
    Abstract [en]

    We present a simple and fast method to simulate spin-torque driven magnetization dynamics in nanopillar spin-valve structures. The approach is based on the coupling between a spin transport code based on random matrix theory and a micromagnetics finite-elements software. In this way the spatial dependence of both spin transport and magnetization dynamics is properly taken into account. Our results are compared with experiments. The excitation of the spin-wave modes, including the threshold current for steady-state magnetization precession and the nonlinear frequency shift of the modes are reproduced correctly. The giant magneto resistance effect and the magnetization switching also agree with experiment. The similarities with recently described spin-caloritronics devices are also discussed.

  • 11. Borlenghi, Simone
    et al.
    Mahani, M. Reza
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Fransson, Jonas
    Nanoscale control of heat and spin conduction in artificial spin chains2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 13, article id 134419Article in journal (Refereed)
    Abstract [en]

    We describe a mechanism to control the energy and magnetization currents in an artificial spin chain, consisting of an array of permalloy nanodisks coupled through a magnetodipolar interaction. The chain is kept out of equilibrium by two thermal baths with different temperatures connected to its ends, which control the current propagation. Transport is enhanced by applying a uniform radio-frequency pump field resonating with some of the spin-wave modes of the chain. Moreover, the two currents can be controlled independently by tuning the static field applied on the chain. Thus we describe two effective means for the independent control of coupled currents and the enhancement of thermal and spin-wave conductivity in a realistic magnonics device, suggesting that similar effects could be observed in a large class of nonlinear oscillating systems.

  • 12.
    Borlenghi, Simone
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wang, Weiwei
    Fangohr, Hans
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Designing a Spin-Seebeck Diode2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 4, p. 047203-Article in journal (Refereed)
    Abstract [en]

    Using micromagnetic simulations, we have investigated spin dynamics in a spin-valve bilayer in the presence of a thermal gradient. The direction and the intensity of the gradient allow us to excite the spin wave modes of each layer selectively. This permits us to synchronize the magnetization precession of the two layers and to rectify the flows of energy and magnetization through the system. Our study yields promising opportunities for applications in spin caloritronics and nanophononics devices.

  • 13.
    Cao, Weimin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Theoretical investigation of sulfur adsorption on FE (100)2009In: TMS 2009 138TH ANNUAL MEETING & EXHIBITION - SUPPLEMENTAL PROCEEDINGS, VOL 3: GENERAL PAPER SELECTIONS, WARRENDALE: MINERALS, METALS & MATERIALS SOC , 2009, p. 523-528Conference paper (Refereed)
    Abstract [en]

    The electronic and structural properties of atomic sulfur adsorbed on the iron surface (100) are examined by using density functional theory (DFT). The sulfur coverage is considered from a quarter of one monolayer (ML) to a full monolayer, and the adsorption energy and work function are calculated for three different adsorption sites of sulfur. Our calculated results indicate that the most likely site for S adsorption is the hollow site on Fe (100), which is agreement with experiment. In addition, at 1 ML coverage, the work function increased after the S adsorption on the Fe (100) surface, which implies that charge transfer from the surface to sulfur has taken place. The results are in agreement with previous theoretical work.

  • 14.
    Cao, Weimin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Delin, Anna
    Seetharaman, Sesadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Coverage dependence of sulfur adsorption on Fe(100): Density functional calculationsIn: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235XArticle in journal (Refereed)
  • 15.
    Cao, Weimin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Calculation of Oxygen and Sulfur Average Velocity on the Iron Surface: A Two-dimensional Gas Model Study2010In: Steel Research International, ISSN 1611-3683, Vol. 81, no 11, p. 949-952Article in journal (Refereed)
    Abstract [en]

    In the present work, a two-dimensional (2D) gas model is derived and used to simulate the average velocity of individual atoms of the surface active elements oxygen and sulfur on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and minimal energy barrier. The calculated results are based on data from density functional calculations combined with thermodynamics and statistical physics. The calculated average velocity of oxygen on the Fe (100) is lower than that of sulphur. This is because of the stronger interaction between oxygen and the first iron layer. We conclude that our simple 2D gas model may be useful for simulating and understanding the complex interfacial phenomena in the steelmaking refining process from an atomic point of view.

  • 16.
    Cao, Weimin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Effect of electronic structure and magnetism on S adsorption on Fe (100) from first principlesIn: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215Article in journal (Other academic)
  • 17. Chico, Jonathan
    et al.
    Etz, Corina
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Eriksson, Olle
    Fransson, Jonas
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Uppsala Univ, Sweden.
    Bergman, Anders
    Thermally driven domain-wall motion in Fe on W(110)2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 1, p. 014434-Article in journal (Refereed)
    Abstract [en]

    It has recently been shown that domain walls (DWs) in ferromagnets can be moved in the presence of thermal gradients. In this work we study the motion of narrow domain walls in low-dimensional systems when subjected to thermal gradients. The system chosen is a monolayer of Fe on W(110) which is known to exhibit a large anisotropy while having a soft exchange, resulting in a very narrow domain wall. The study is performed by means of atomistic spin dynamics simulations coupled to first-principles calculations. By subjecting this system to thermal gradients we observe a temperature-dependent movement of the domain wall. The thermal gradient always makes the domain wall move towards the hotter region of the sample with a velocity proportional to the gradient. Our material specific study is complemented by model simulations to discern the interplay between the thermal gradient, magnetic anisotropy, and the exchange interaction and shows that the larger DW velocities are found for materials with broader domain-wall width. The relatively slow DW motion of the Fe/W(110) system is hence primarily caused by its narrow domain-wall width, which results from its large magnetic anisotropy and soft exchange.

  • 18.
    Delin, Anna
    KTH, Superseded Departments, Materials Science and Engineering.
    First-principles calculations of the II-VI semiconductor beta-HgS: Metal or semiconductor2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, no 15Article in journal (Refereed)
    Abstract [en]

    Relativistic all-electron full-potential first-principles calculations have been performed in order to study the symmetry of the energy levels around the valence band maximum in the zinc blende II-VI semiconductors beta-HgS, HgSe, and HgTe. It is demonstrated that in general, an inverted band-structure does not necessarily lead to a zero fundamental energy gap for systems with zinc blende symmetry. Specifically, beta-HgS is found to have at the same time an inverted band structure, and a small, slightly indirect, fundamental energy gap. Possibly, the energy levels around the valence band maximum order differently in each of these systems.

  • 19.
    Delin, Anna
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Kluner, T.
    Excitation spectra and ground-state properties from density-functional theory for the inverted band-structure systems beta-HgS, HgSe, and HgTe2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 3Article in journal (Refereed)
    Abstract [en]

    We have performed a systematic density-functional study of the mercury chalcogenide compounds beta-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas beta-HgS has a small spin-orbit-induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional. We also address the problem of treating relativistic p electrons with methods based on a scalar-relativistic basis set and show that the effect is rather small for the present systems.

  • 20.
    Delin, Anna
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Tosatti, E
    Emerging magnetism in platinum nanowires2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 566, p. 262-267Article in journal (Refereed)
    Abstract [en]

    We have investigated infinitely long, monostrand Pt nanowires theoretically, and found that they exhibit Hund's rule magnetism. We find a spin moment of 0.6 mu(B) per atom, at the equilibrium bond length. Its magnetic moment increases with stretching. The origin of the wire magnetism is analyzed and its effect on the conductance through the wire is discussed.

  • 21.
    Delin, Anna
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Tosatti, E.
    The electronic structure of 4d transition-metal monatomic wires2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 45, p. 8061-8074Article in journal (Refereed)
    Abstract [en]

    Monatomic nanowires of the nonmagnetic transition metals Ru, Rh, and Pd have been studied theoretically, using first-principles computational techniques, in order to investigate the possible onset of magnetism in these nanosystems. Our fully relativistic spin-polarized all-electron density functional calculations reveal the onset of Hund's rule magnetism in nanowires of all three metals, with mean-field moments of 1.1, 0.3, and 0.7 mu(B), respectively, at the equilibrium bond length. An analysis of the band structures indicates that the nanocontact superparamagnetic state suggested by our calculations should affect the ballistic conductance between tips made of Ru, Rh or Pd, leading to possible temperature and magnetic field dependent conductance.

  • 22.
    Delin, Anna
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tosatti, E.
    Weht, R.
    Delin, Tosatti, and Weht Reply2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 7Article in journal (Refereed)
  • 23.
    Delin, Anna
    et al.
    ICTP, Trieste, Italy.
    Tosatti, Erio
    ICTP, Trieste, Italy.
    Weht, Ruben
    Comis Nacl Energia Atom, Dept Fis, RA-1650 San Martin, Argentina.
    Magnetism in atomic-size palladium contacts and nanowires2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 5, p. 057201-572014Article in journal (Refereed)
    Abstract [en]

    Palladium (Pd) nanowires, that exhibit Hund's rule magnetism are investigated. A spin moment of 0.7μB per atom is found in long, monostrand nanowires. The predicted moment is about 0.3μB per nanowire atom for short, monostrand nanowires between bulk leads. Results show that a coaxial (6,1) nanowire was nonmagnetic in nature.

  • 24. Durrenfeld, P.
    et al.
    Gerhard, F.
    Chico, J.
    Dumas, R. K.
    Ranjbar, M.
    Bergman, A.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Gould, C.
    Molenkamp, L. W.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. University of Gothenburg, Sweden; NanOsc AB, Sweden.
    Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 21, article id 214424Article in journal (Refereed)
    Abstract [en]

    The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic resonance (FMR) measurements and calculations from first principles to investigate how the composition of the epitaxially grown NiMnSb influences the magnetodynamic properties of saturation magnetization M-S, Gilbert damping alpha, and exchange stiffness A. M-S and A are shown to have a maximum for stoichiometric composition, while the Gilbert damping is minimum. We find excellent quantitative agreement between theory and experiment for M-S and alpha. The calculated A shows the same trend as the experimental data but has a larger magnitude. In addition to the unique in-plane anisotropy of the material, these tunabilities of the magnetodynamic properties can be taken advantage of when employing NiMnSb films in magnonic devices.

  • 25.
    Elgammal, Karim
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Superseded Departments (pre-2005), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Adsorption of carbon dioxide and water molecules on graphene on top of silica substrates: dispersion corrected density functional calculationsManuscript (preprint) (Other academic)
    Abstract [en]

    We report on systematic computational studies of carbon dioxide and water molecule adsorption on graphene, with the graphene layer deposited on top of a substrate. Specifically, we address the influence of cristobalite and quartz substrates, i.e. two different types of silicon dioxide. The computations are based on density functional theory (DFT), with a nonempirical nonlocal van der Waals density functional included to account for dispersion forces.We calculate the binding energies and equilibrium positions of the molecules, as well as charge transfer and how the charge density of the graphene layer changes due to the interactions with the substrate and the molecules. The molecule-graphene bonding distances are found to be in the range 3.3-3.4 Å, and the graphene-substrate bonding distances around 3.6 Å. These values are slightly larger than what we have found previously, using an empirical expression for the van der Waals density functional. At the same time, the values for the binding energies are increased, compared to what we have obtained in a previous study. We find, in all cases, a net electron transfer from the adsorbed molecule to the graphene+substrate system. For quartz, the total charge transfer is between 0.1 and 0.2 electrons per adsorbed molecule. For cristobalite, it is only about a tenth of that. Our findings are consistent with earlier calculations as well as experimental data.

  • 26.
    Elgammal, Karim
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Superseded Departments (pre-2005), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Graphene adhesion on surfaces: a van der Waals density functional studyManuscript (preprint) (Other academic)
    Abstract [en]

    We present a van der Waals density functional (vdW-DF) calculations study of graphene adhesion to different types of substrates with different surface conditions. The study expands to both metal and semiconductor substrates with different surface endings. All substrate surfaces were the 111 surfaces where they have hexagonal lattice parameters perfectly matching with the graphene's. Adsorption geometries, energies, bader charges, dipole moments and electronic structure in terms of density of states are investigated. The results are showing a general agrement with both experimental results as well as theoritical findings done with similar setup. The results reveal that the degree of adhesive of graphene to different surfaces can affect the electronic structure of graphene ending in having different applications when designing graphene in building nano-electronic devices.

  • 27.
    Elgammal, Karim
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hugosson, Håkan W.
    Smith, Anderson D.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. Chalmers Institute of Technology, Sweden.
    Råsander, Mikael
    Bergqvist, Lars
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Density functional calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates2017In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 663, p. 23-30Article in journal (Refereed)
    Abstract [en]

    We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 (A) over circle. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.

  • 28.
    Elgammal, Karim
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Hugosson, Håkan W.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Smith, Anderson D.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Råsander, Mikael
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Density functional theory calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substratesManuscript (preprint) (Other academic)
  • 29.
    Fan, Xuge
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Elgammal, Karim
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Smith, Anderson D.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre. Department of Physics and Astronomy, Materials Theory Division, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Lemme, Max C.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits. Department of Electronic Devices, RWTH Aachen University, 52074 Aachen, Germany.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Humidity and CO2 gas sensing properties of double-layer graphene2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 127, p. 576-587Article in journal (Refereed)
    Abstract [en]

    Graphene has interesting gas sensing properties with strong responses of the graphene resistance when exposed to gases. However, the resistance response of double-layer graphene when exposed to humidity and gasses has not yet been characterized and understood. In this paper we study the resistance response of double-layer graphene when exposed to humidity and CO2, respectively. The measured response and recovery times of the graphene resistance to humidity are on the order of several hundred milliseconds. For relative humidity levels of less than ~ 3% RH, the resistance of double-layer graphene is not significantly influenced by the humidity variation. We use such a low humidity atmosphere to investigate the resistance response of double-layer graphene that is exposed to pure CO2 gas, showing a consistent response and recovery behaviour. The resistance of the double-layer graphene decreases linearly with increase of the concentration of pure CO2 gas. Density functional theory simulations indicate that double-layer graphene has a weaker gas response compared to single-layer graphene, which is in agreement with our experimental data. Our investigations contribute to improved understanding of the humidity and CO2 gas sensing properties of double-layer graphene which is important for realizing viable graphene-based gas sensors in the future.

  • 30.
    Hugosson, Håkan Wilhelm
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Cao, Weimin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sulfur- and Oxygen-Induced Alterations of the Iron (001) Surface Magnetism and Work Function: A Theoretical Study2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 12, p. 6161-6171Article in journal (Refereed)
    Abstract [en]

    The electronic structure and magnetic properties of atomic sulfur and oxygen adsorbed on the iron (001) surface are examined using density functional theory (DFT). The sulfur/oxygen coverage is considered from a quarter of one monolayer (ML) to a full monolayer. The work function change, magnetic properties, and density of states are determined and compared. We find that the work function increases with sulfur coverage in agreement with experiment. We also find that sulfur interacts strongly with the surface layer and that the magnetic moment of the Fe surface decreases as the sulfur coverage increases. In the case of oxygen adsorption, we find that the magnetic moment of the surface Fe atoms instead increases. We show that the difference in surface magnetic moment between sulfur adsorption and oxygen adsorption can be simply explained combining the Slater-Pauling rigid band model linking d-occupation and magnetic moment with an electronegativity argument. Moreover, the work function of the Fe surface as a function of oxygen coverage is found to be very sensitive to overlayer arrangement, here seen in the cases of 0.5 ML c(2 x 2) and 0.5 ML p(2 x 1). This is shown to result from large differences in the surface dipole moment change induced by the oxygen adsorption in the two different overlayer arrangements.

  • 31.
    Huttmann, Felix
    et al.
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Rothenbach, Nico
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Kraus, Stefan
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Ollefs, Katharina
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Arruda, Lucas M.
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Bernien, Matthias
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Thonig, Danny
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Fransson, Jonas
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Kummer, Kurt
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Brookes, Nicholas B.
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Kuch, Wolfgang
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Michely, Thomas
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Wende, Heiko
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 5, p. 911-917Article in journal (Refereed)
    Abstract [en]

    We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M-5,M-4 edge XMCD, orbital and spin magnetic moments of (-0.1 +/- 0.3)mu(B) and (+7.0 +/- 0.6)mu(B), respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M-5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower.

  • 32. Joyce, J. J.
    et al.
    Wills, J. M.
    Durakiewicz, T.
    Butterfield, M. T.
    Guziewicz, E.
    Moore, D. P.
    Sarrao, J. L.
    Morales, L. A.
    Arko, A. J.
    Eriksson, O.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Graham, K. S.
    Dual nature of the 5f electrons in plutonium materials2006In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 378-80, p. 920-924Article in journal (Refereed)
    Abstract [en]

    The electronic structure of select Pu materials is examined by means of photoemission (PES) and model calculations. We present the first photoemission results and electronic structure calculations for the material PuIn3. Results for Pu materials, including the cubic delta-phase metal and the superconductor PuCoGa5, give indication of the 5f electrons exhibiting both localized and itinerant character. These new results for PuIn3 place this compounds also in the 5f dual nature category. The dual nature of the Pu 5f electrons demarks the boundary between localized and itinerant 5f character in the actinides. The photoemission data for delta-Pu, PuIn3 and PuCoGa5 are compared against model calculations. The calculations are a mixed level model (MLM) which is a multi-electron extension of the generalized gradient approximation. Using the MLM, one obtains good agreement for the volume and total energy minimum with 4 of 5 Pu 5f electrons localized. The calculations also agree well with the PES spectra. Other computational schemes and interpretations are also reviewed.

  • 33. Kanchana, V.
    et al.
    Vaitheeswaran, G.
    Alouani, M.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Electronic structure and x-ray magnetic circular dichroism of Sr2FeMoO6: Ab initio calculations2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 22Article in journal (Refereed)
    Abstract [en]

    Theoretical investigations of the electronic structure, x-ray absorption, and x-ray magnetic circular dichroism (XMCD) at the Fe L-2,L-3 and Mo L-2,L-3 edges of Sr2FeMoO6 are carried out by means of the generalized gradient approximation. The magnetic coupling between Fe and Mo is found to be antiparallel, which gives direct confirmation of ferrimagnetic ordering and settles controversies existing between the earlier experimental reports. This is also confirmed by our good agreement of the Mo L-2,L-3 edges with experiment. Using our theoretical spectra, we recalculate the spin and orbital magnetic moments by means of the XMCD sum rules and compare the results with a direct self-consistent calculation and experiment.

  • 34. Kanchana, V.
    et al.
    Vaitheeswaran, G.
    Svane, A.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    First-principles study of elastic properties of CeO2, ThO2 and PoO22006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 42, p. 9615-9624Article in journal (Refereed)
    Abstract [en]

    Using first-principles density functional calculations, the structural and elastic properties of fluorite type oxides CeO2, ThO2 and PoO2 were studied by means of the full-potential linear muffin-tin orbital method. Calculations were performed within the local density approximation (LDA) as well as generalized gradient approximation (GGA) to the exchange correlation potential. The calculated equilibrium lattice constants and bulk moduli are in good agreement with the experimental results, as are the computed elastic constants for CeO2 and ThO2. For PoO2 this is the first quantitative theoretical prediction of the ground state properties, and it still awaits experimental confirmation. The calculations find PoO2 to be a semiconductor with an indirect band gap and elastic constants similar in magnitude to those of CeO2 and ThO2.

  • 35. Keshavarz, S.
    et al.
    Kvashnin, Y. O.
    Di Marco, I.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, 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 correlations2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 16, article id 165129Article in journal (Refereed)
    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.

  • 36. Krockenberger, Y.
    et al.
    Mogare, K.
    Reehuis, M.
    Tovar, M.
    Jansen, M.
    Vaitheeswaran, G.
    Kanchana, V.
    Bultmark, F.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Wilhelm, F.
    Rogalev, A.
    Winkler, A.
    Alff, L.
    Sr2CrOsO6: End point of a spin-polarized metal-insulator transition by 5d band filling2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 2Article in journal (Refereed)
    Abstract [en]

    In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined experimental results confirm the existence of a sizable induced magnetic moment at the Os site, supported by band-structure calculations, in agreement with a proposed kinetic-energy-driven mechanism of ferrimagnetism in these compounds. The intriguing property of Sr2CrOsO6 is that it is at the end point of a metal-insulator transition due to 5d band filling and at the same time ferrimagnetism and high-spin polarization are preserved.

  • 37. Locht, I. L. M.
    et al.
    Di Marco, I.
    Garnerone, S.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Battiato, M.
    Ultrafast magnetization dynamics: Microscopic electronic configurations and ultrafast spectroscopy2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 6, article id 064403Article in journal (Refereed)
    Abstract [en]

    We provide an approach for the identification of the electronic and magnetic configurations of ferromagnetic Fe after an ultrafast decrease or increase of the magnetization. The model is based on the well-grounded assumption that, after an ultrafast variation of the magnetization, the system achieves a partial thermal equilibrium. With statistical arguments we show that the magnetic configurations are qualitatively different in the case of reduced or increased magnetization. The predicted magnetic configurations are then used to compute the dielectric response at the 3p (M) absorption edge, which is directly related to the changes observed in the experimental T-MOKE data. The good qualitative agreement between theory and experiment offers a substantial support for the validity of the model, and to the very existence of an ultrafast increase of the magnetization.

  • 38. Locht, I. L. M.
    et al.
    Kvashnin, Y. O.
    Rodrigues, D. C. M.
    Pereiro, M.
    Bergman, A.
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Lichtenstein, A. I.
    Katsnelson, M. I.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Klautau, A. B.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Di Marco, I.
    Eriksson, O.
    Standard model of the rare earths analyzed from the Hubbard I approximation2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 8, article id 085137Article in journal (Refereed)
    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.

  • 39. Lundgren, E.
    et al.
    Andersen, J. N.
    Nyholm, R.
    Torrelles, X.
    Rius, J.
    Delin, Anna
    Grechnev, A.
    Eriksson, O.
    Konvicka, C.
    Schmid, M.
    Varga, P.
    Geometry of the valence transition induced surface reconstruction of Sm(0001)2002In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, no 13Article in journal (Refereed)
    Abstract [en]

    We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and ab initio calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the 4f electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.

  • 40.
    Mahani, Mohammad Reza
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Mirsakiyeva, Amina
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Breakdown of Polarons in Conducting Polymers at Device Field Strengths2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 19, p. 10317-10324Article in journal (Refereed)
    Abstract [en]

    Conducting polymers have become standard engineering materials used in many electronic devices. Despite this, there is a lack of understanding of the microscopic origin of the conducting properties, especially at realistic device field strengths. We present simulations of doped poly(p-phenylene) (PPP) using a Su-Schrieffer-Heeger (SSH) tight-binding model, with the electric field included in the Hamiltonian through a time-dependent vector potential via Peierls substitution of the phase factor. We find that polarons typically break down within less than a picosecond after the field has been switched on, already for electric fields as low as around 1.6 mV/angstrom. This is a field strength common in many flexible organic electronic devices. Our results challenge the relevance of the polaron as charge carrier in conducting polymers for a wide range of applications.

  • 41.
    Mahani, Mohammad Reza
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Mirsakiyeva, Amina
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Department of Physics and Astronomy, Materials Theory Division, Uppsala University,.
    Charge transport via polarons in doped poly(p-phenylene) with impurityManuscript (preprint) (Other academic)
    Abstract [en]

    Polaron charge transport in doped poly(p-phenylene), PPP, in the presence of magnetic and nonmagnetic impurities and an electric field, is studied using the Su-Schrieffer-Heeger (SSH) tight-binding model. In our approach, the electric field is included in the Hamiltonian through the time-dependent vector potential via Peierls substitution of the phase factor. We describe the dynamics of the polarons and identify three distinct regimes: transmission, reflection, and trapping of polarons at the impurity site. The strength of the electric field as well as the impurity potential determine the outcome ofthe scattering.

  • 42. Majewski, P.
    et al.
    Geprags, S.
    Boger, A.
    Opel, M.
    Erb, A.
    Gross, R.
    Vaitheeswaran, G.
    Kanchana, V.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Wilhelm, F.
    Rogalev, A.
    Alff, L.
    Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 13Article in journal (Refereed)
    Abstract [en]

    We have investigated the magnetic moment of the W ion in the ferrimagnetic double perovskites Sr2CrWO6 and Ca2CrWO6 by x-ray magnetic circular dichroism at the W L-2,L-3 edges. In both compounds a finite negative spin and positive orbital magnetic moment was detected. The experimental results are in good agreement with band-structure calculations for (Sr/Ca)(2)CrWO6 using the full-potential linear muffin-tin orbital method. It is remarkable that the magnetic ordering temperature, T-C, is correlated with the magnetic moment at the nonmagnetic W atom.

  • 43.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Botkina, D.
    Elgammal, Karim
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Ten, Assel
    Hugosson, Håkan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University.
    Yu, Valentina
    Experimental and ab initio studies of the novel piperidine-containing acetylene glycolsManuscript (preprint) (Other academic)
  • 44.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Kazakh-British Technical University, Kazakhstan.
    Botkina, Darya
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. Institute of Chemical Sciences, Kazakhstan.
    Elgammal, Karim
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Ten, Assel
    Hugosson, Håkan W.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Yu, Valentina
    Experimental and density functional theory studies of some novel piperidine-containing acetylene glycols2016In: ARKIVOC, ISSN 1551-7004, E-ISSN 1551-7012, p. 86-99Article in journal (Refereed)
    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.

  • 45.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hugosson, Håkan W.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Univ Gävle, Sweden.
    Crispin, Xavier
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Quantum Molecular Dynamical Calculations of PEDOT 12-Oligomer and its Selenium and Tellurium Derivatives2017In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 46, no 5, p. 3071-3075Article in journal (Refereed)
    Abstract [en]

    We present simulation results, computed with the Car-Parrinello molecular dynamics method, at zero and ambient temperature (300 K) for poly(3,4-ethylenedioxythiophene) [PEDOT] and its selenium and tellurium derivatives PEDOS and PEDOTe, represented as 12-oligomer chains. In particular, we focus on structural parameters such as the dihedral rotation angle distribution, as well as how the charge distribution is affected by temperature. We find that for PEDOT, the dihedral angle distribution shows two distinct local maxima whereas for PEDOS and PEDOTe, the distributions only have one clear maximum. The twisting stiffness at ambient temperature appears to be larger the lighter the heteroatom (S, Se, Te) is, in contrast to the case at 0 K. As regards point charge distributions, they suggest that aromaticity increases with temperature, and also that aromaticity becomes more pronounced the lighter the heteroatom is, both at 0 K and ambient temperature. Our results agree well with previous results, where available. The bond lengths are consistent with substantial aromatic character both at 0 K and at ambient temperature. Our calculations also reproduce the expected trend of diminishing gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital with increasing atomic number of the heteroatom.

  • 46.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hugosson, Håkan W.
    Linares, Mathieu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics. 5)Department of Physics and Astronomy, Materials Theory Division, Uppsala University.
    Temperature dependence of band gaps and conformational disorder in PEDOT and its selenium and tellurium derivatives: density functional calculations2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Refereed)
    Abstract [en]

    The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexibleelectronics. We present combined molecular dynamics and quantum chemical calculations, based on den-sity functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS andEDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems.With finite size scaling, we also extrapolate our results to the infinite polymers, i.e. PEDOT, PEDOS and PEDOTe. Our computations indicate that the most favourable oligomer conformations at finite temperature are conformations around the flat trans-conformation and a non-flat conformation around 45 from the cis-conformation. Also, the dihedral stiffness increases with the atomic number of the heteroatom. We find excellent agreement with experimentally measured gaps for PEDOT and PEDOS. For PEDOT, the gap does not increase with temperature where as this is the case for its derivatives. The conformational disorder as well as the choice of basis set both significantly affect the calculated gaps.

  • 47.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linares, Mathieu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Department of Physics and Astronomy, Materials Theory Division, Uppsala University,.
    Optical properties of Naphthobischalcogenadiazoles from density functional perspectiveManuscript (preprint) (Other academic)
    Abstract [en]

    In the present work the density functional calculations of two naphthobischalcogenadiazole (NXz) oligomers are shown. The oxygen- and sulphur-containing NXz trimers were optimized in a form of a neutral oligomer and a radical cation in order to investigate structural changes resulting from the polaron formation. The influence of polaron on band gaps is determined and supported with densities of states analysis together with absorption spectra. This manuscript used B3LYP and ωB97XD functionals in combination with 6-31+G(d) basis set.

  • 48.
    Mirsakiyeva, Amina
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Linares, Mathieu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Department of Physics and Astronomy, Materials Theory Division, Uppsala University,.
    Polaron formation and optical absorption in PEDOT and its selenium and tellurium derivatives: density functional calculationsManuscript (preprint) (Other academic)
    Abstract [en]

    We present a density functional theory (DFT) study on polaron formation and optical properties of PEDOT and its selenium and tellurium derivatives. Comparing a number of combinations of basis set and approximations to the exchange-correlation functional, we find that the ωB97XD functional is an overall good choice giving well-localized polarons and optical spectra in good agreement with experiment. This functional has the correct long-range  asymptotic behavior, and also includes some short-range Hartree-Fock exchange. Despite the  long-range Hartree-Fock exchange part present in this functional, the spin contamination remains relatively limited and it also stably produces results that are virtually independent of the basis set used.

  • 49.
    Odell, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab Initio Study of Switching Properties of Photochromic Dithienylethene Molecules2006In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 965, p. 296-300Article in journal (Refereed)
    Abstract [en]

    We report an ab initio study of a photochromic dithienylethene derivative. The mechanisms for switching between open and closed conformations are investigated based on total energy calculations for the ground and first excited state. An explanation for the central ring closure based on relaxation of the excited state is presented.

  • 50.
    Odell, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ab initio study of the electron transport in dithienylethene photochromic molecules attached to gold leads2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 5, p. 052061-Article in journal (Refereed)
    Abstract [en]

    We report a theoretical study of single molecule conduction in open and closed conformations of photochromic dithienylethene molecules attached to metallic leads. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conducting behavior. We also investigate the switching behavior of the molecule based on total energy calculations for intermediate conformations along the reaction path. The results are compared to earlier work.

12 1 - 50 of 93
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