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  • 1.
    Arapan, S.
    et al.
    IT4Innovations, VSB-Technical University of Ostrava, Ostrava-Poruba, Czech Republic; ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, University of Burgos, Burgos, Spain.
    Nieves, P.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, University of Burgos, Burgos, Spain.
    Cuesta-Lopez, S.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, University of Burgos, Burgos, Spain; ICAMCyL, International Center for Advanced Materials and Raw Materials of Castilla y Léon, Léon, Spain.
    Gusenbauer, M.
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Oezelt, H.
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Schrefl, T.
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Delczeg-Czirjak, E. K.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Herper, H. C.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Influence of antiphase boundary of the MnAl tau-phase on the energy product2019In: Physical Review Materials, ISSN 2475-9953, Vol. 3, no 6, article id 064412Article in journal (Refereed)
    Abstract [en]

    In this paper, we use a multiscale approach to describe a realistic model of a permanent magnet based on MnAl tau-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performing micromagnetic simulations. For an accurate estimation of the energy product of a realistic permanent magnet based on the MnAl tau-phase with antiphase boundaries, we quantify exchange interaction strength across the antiphase boundary defect with a simple approach derived from first-principles calculations. These two types of calculations, performed at different scales, are linked via atomistic spin-dynamics simulations.

  • 2.
    Bondarenko, N.
    et al.
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Skorodumova, N. , V
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Multiscale Materials Modelling, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Pereiro, M.
    Division of Materials theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 41, article id 415401Article in journal (Refereed)
    Abstract [en]

    Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrodinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that dnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.

  • 3.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Searching for materials with reduced dimension2018In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 13, no 3, p. 180-181Article in journal (Refereed)
  • 4.
    Hasan, Mehedi
    et al.
    ITMO University, Saint Petersburg, Russia; Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore.
    Yudin, Dmitry
    ITMO University, Saint Petersburg, Russia.
    Iorsh, Ivan
    ITMO University, Saint Petersburg, Russia; Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Shelykh, Ivan
    ITMO University, Saint Petersburg, Russia; Science Institute, University of Iceland, Reykjavik, Iceland.
    Topological edge-state engineering with high-frequency electromagnetic radiation2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 20, article id 205127Article in journal (Refereed)
    Abstract [en]

    We outline here how strong light-matter interaction can be used to induce quantum phase transition between normal and topological phases in two-dimensional topological insulators. We consider the case of a HgTe quantum well, in which band inversion occurs above a critical value of the well thickness, and demonstrate that coupling between electron states and the E field from an off-resonant linearly polarized laser provides a powerful tool to control topological transitions, even for a thickness of the quantum well that is below the critical value. We also show that topological phase properties of the edge states, including their group velocity, can be tuned in a controllable way by changing the intensity of the laser field. These findings open up the possibility for new experimental means with which to investigate topological insulators and shed new light on topological-insulator-based technologies that are under active discussion.

  • 5.
    Hedlund, Daniel
    et al.
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Cedervall, Johan
    Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Edström, Alexander
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Materials Theory, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland.
    Werwinski, Miroslaw
    Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland.
    Kontos, Sofia
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Rusz, Jan
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Svedlindh, Peter
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Sahlberg, Martin
    Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Gunnarsson, Klas
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Magnetic properties of the Fe5SiB2-Fe5PB2 system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094433Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of the compound Fe5Si1-xPxB2 have been studied, with a focus on the Curie temperature T-C, saturation magnetization MS, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine T-C(x) and M-S(x). The saturation magnetization at 10 K (300 K) is found to monotonically decrease from 1.11 MA/m (1.03 MA/m) to 0.97 MA/m (0.87 MA/m), as x increases from 0 to 1. The Curie temperature is determined to be 810 and 615 K in Fe5SiB2 and Fe5PB2, respectively. The highest T-C is observed for x = 0.1, while it decreases monotonically for larger x. The Curie temperatures have also been theoretically determined to be 700 and 660 K for Fe5SiB2 and Fe5PB2, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low-field magnetization vs temperature results for x = 0,0.1,0.2 indicate that there is a transition from easy-axis to easy-plane anisotropy with decreasing temperature.

  • 6.
    Hellsvik, Johan
    et al.
    Nordita, Stockholm, Sweden; Department of Physics, KTH Royal Institute of Technology, Sweden.
    Thonig, Danny
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Modin, Klas
    Department of Mathematics, Chalmers University of Technology, Gothenburg, Sweden; Department of Mathematics, University of Gothenburg, Gothenburg, Sweden.
    Iusan, Diana
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Bergqvist, Lars
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Electrum 229, Kista, Sweden; SeRC (Swedish e-Science Research Center), KTH Royal Institute of Technology, Stockholm, Sweden.
    Delin, Anna
    Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Electrum 229, Kista, Sweden; SeRC (Swedish e-Science Research Center), KTH Royal Institute of Technology, Stockholm, Sweden; Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    General method for atomistic spin-lattice dynamics with first-principles accuracy2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104302Article in journal (Refereed)
    Abstract [en]

    We present a computationally efficient and general first-principles based method for spin-lattice simulations for solids and clusters. The method is based on a coupling of atomistic spin dynamics and molecular dynamics simulations, expressed through a spin-lattice Hamiltonian, where the bilinear magnetic term is expanded up to second order in displacement. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and we observe good agreement with previous simulations. We also illustrate the coupled spin-lattice dynamics method on a more conceptual level, by exploring dissipation-free spin and lattice motion of small magnetic clusters (a dimer, trimer, and tetramer). The method discussed here opens the door for a quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.

  • 7.
    Herper, H. C.
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Ahmed, T.
    Institute for Materials Science, Los Alamos National Laboratory, Los Alamos NM, USA.
    Wills, J. M.
    Theoretical Division, Los Alamos National Laboratory, Los Alamos NM, USA.
    Di Marco, I.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Björkman, T.
    Department of Natural Sciences, Åbo Akademi, Turku, Finland.
    Iusan, D.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Balatsky, A. V.
    Institute for Materials Science, Los Alamos National Laboratory, Los Alamos NM, USA; AlbaNova University Center Nordita, Stockholm, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Combining electronic structure and many-body theory with large databases: A method for predicting the nature of 4 f states in Ce compounds2017In: Physical Review Materials, ISSN 2475-9953, Vol. 1, no 3, article id 033802Article in journal (Refereed)
    Abstract [en]

    Recent progress in materials informatics has opened up the possibility of a new approach to accessing properties of materials in which one assays the aggregate properties of a large set of materials within the same class in addition to a detailed investigation of each compound in that class. Here we present a large scale investigation of electronic properties and correlated magnetism in Ce-based compounds accompanied by a systematic study of the electronic structure and 4f-hybridization function of a large body of Ce compounds. We systematically study the electronic structure and 4f-hybridization function of a large body of Ce compounds with the goal of elucidating the nature of the 4f states and their interrelation with the measured Kondo energy in these compounds. The hybridization function has been analyzed for more than 350 data sets (being part of the IMS database) of cubic Ce compounds using electronic structure theory that relies on a full-potential approach. We demonstrate that the strength of the hybridization function, evaluated in this way, allows us to draw precise conclusions about the degree of localization of the 4f states in these compounds. The theoretical results are entirely consistent with all experimental information, relevant to the degree of 4f localization for all investigated materials. Furthermore, a more detailed analysis of the electronic structure and the hybridization function allows us to make precise statements about Kondo correlations in these systems. The calculated hybridization functions, together with the corresponding density of states, reproduce the expected exponential behavior of the observed Kondo temperatures and prove a consistent trend in real materials. This trend allows us to predict which systems may be correctly identified as Kondo systems. A strong anticorrelation between the size of the hybridization function and the volume of the systems has been observed. The information entropy for this set of systems is about 0.42. Our approach demonstrates the predictive power of materials informatics when a large number of materials is used to establish significant trends. This predictive power can be used to design new materials with desired properties. The applicability of this approach for other correlated electron systems is discussed.

  • 8.
    Huang, Shuo
    et al.
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Holmstrom, Erik
    Sandvik Coromant R&D, Stockholm, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Vitos, Levente
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden; Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Budapest, Hungary.
    Mapping the magnetic transition temperatures for medium- and high-entropy alloys2018In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 95, p. 80-84Article in journal (Refereed)
    Abstract [en]

    Tailorable magnetic state near room temperature is very promising for several technological, including magnetocaloric applications. Here using first-principle alloy theory, we determine the Curie temperature (T-C) of a number of equiatomic medium- and high-entropy alloys with solid solution phases. All calculations are performed at the computed lattice parameters, which are in line with the available experimental data. Theory predicts a large crystal structure dependence of T-C, which explains the experimental observations under specified conditions. The sensitivity of the magnetic state to the crystal lattice is reflected by the magnetic exchange interactions entering the Heisenberg Hamiltonian. The analysis of the effect of composition on T-C allows researchers to explore chemistry-dependent trends and design new multi-component alloys with pre-assigned magnetic properties.

  • 9.
    Huttmann, Felix
    et al.
    II. Physikalisches Institut, Universität zu Köln, Köln, Germany.
    Rothenbach, Nico
    Fakultät für Physik, Universität Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CENIDE), German.
    Kraus, Stefan
    II. Physikalisches Institut, Universität zu Köln, Köln, Germany.
    Ollefs, Katharina
    Fakultät für Physik, Universität Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CENIDE), German.
    Arruda, Lucas M.
    Institut für Experimentalphysik, Freie Universität Berlin, Berlin, Germany.
    Bernien, Matthias
    Institut für Experimentalphysik, Freie Universität Berlin, Berlin, Germany.
    Thonig, Danny
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Delin, Anna
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden; Department of Applied Physics, School of Engineering Sciences, KTH Royal Institute of Technology, Kista, Sweden; SeRC (Swedish e-Science Research Center), KTH Royal Institute of Technology, Stockholm, Sweden.
    Fransson, Jonas
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Kummer, Kurt
    European Synchrotron Radiation Facility, Grenoble, France.
    Brookes, Nicholas B
    European Synchrotron Radiation Facility, Grenoble, France.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Kuch, Wolfgang
    Institut für Experimentalphysik, Freie Universität Berlin, Berlin, Germany.
    Michely, Thomas
    II. Physikalisches Institut, Universität zu Köln, Köln, Germany.
    Wende, Heiko
    Fakultät für Physik, Universität Duisburg-Essen and Center for Nanointegration Duisburg-Essen (CENIDE), German.
    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 M5,4 edge XMCD, orbital and spin magnetic moments of (-0.1 ± 0.3)μB and (+7.0 ± 0.6)μB, respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M5 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.

  • 10.
    Jana, S.
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Panda, S. K.
    Centre de Physique Théorique, Ecole Polytechnique, CNRS UMR 7644, Université Paris-Saclay, Palaiseau, France; Department of Physics, Bennett University, Uttar Pradesh, India.
    Phuyal, D.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Pal, B.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Mukherjee, S.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Dutta, A.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Kumar, P. Anil
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Hedlund, D.
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Schött, J.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Thunström, P.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Kvashnin, Y.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Rensmo, H.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Kamalakar, M. Venkata
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Segre, Carlo U.
    CSRRI & Department of Physics, Illinois Institute of Technology, Chicago Illinois, USA.
    Svedlindh, P.
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Gunnarsson, K.
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Biermann, S.
    Centre de Physique Théorique, Ecole Polytechnique, CNRS UMR 7644, Université Paris-Saclay, Palaiseau, France; Collège de France, Paris, France.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Karis, O.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Sarma, D. D.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

  • 11.
    Keshavarz, Samara
    et al.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Kontos, Sofia
    Department of Engineering Sciences, Division of Solid State Physics, Uppsala University, Uppsala, Sweden.
    Wardecki, Dariusz
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden; Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland; Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
    Kvashnin, Yaroslav O.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Pereiro, Manuel
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Panda, Swarup K.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Sanyal, Biplab
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Grins, Jekabs
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Svensson, Gunnar
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.
    Gunnarsson, Klas
    Department of Engineering Sciences, Division of Solid State Physics, Uppsala University, Uppsala, Sweden.
    Svedlindh, Peter
    Department of Engineering Sciences, Division of Solid State Physics, Uppsala University, Uppsala, Sweden.
    Magnetic properties of Ruddlesden-Popper phases Sr3−x Yx (Fe1.25 Ni0.75) O7−δ: A combined experimental and theoretical investigation2018In: Physical Review Materials, E-ISSN 2475-9953, Vol. 2, no 4, article id 044005Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive study of the magnetic properties of Sr3-xYx(Fe1.25Ni0.75)O-7(-delta )(0 <= x <= 0.75). Experimentally, the magnetic properties are investigated using superconducting quantum interference device (SQUID) magnetometry and neutron powder diffraction (NPD). This is complemented by a theoretical study based on density functional theory as well as the Heisenberg exchange parameters. Experimental results show an increase in the Ned temperature (T-N) with an increase of Y concentrations and O occupancy. The NPD data reveal that all samples are antiferromagnetically ordered at low temperatures, which has been confirmed by our theoretical simulations for the selected samples. Our first-principles calculations suggest that the three-dimensional magnetic order is stabilized due to finite interlayer exchange couplings. The latter give rise to finite interlayer spin-spin correlations, which disappear above T-N.

  • 12.
    Koumpouras, Konstantinos
    et al.
    Applied Physics, Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Yudin, Dmitry
    ITMO University, Saint Petersburg, Russia.
    Adelmann, Christoph
    Imec, Leuven, Belgium.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Maison de la Simulation, CEA, CNRS, Univ. Paris-Sud, UVSQ, Université Paris-Saclay, Gif-sur-Yvette, France; INAC-MEM, CEA, Grenoble, France.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    A majority gate with chiral magnetic solitons2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 37, article id 375801Article in journal (Refereed)
    Abstract [en]

    In magnetic materials, nontrivial spin textures may emerge due to the competition among different types of magnetic interactions. Among such spin textures, chiral magnetic solitons represent topologically protected spin configurations with particle-like properties. Based on atomistic spin dynamics simulations, we demonstrate that these chiral magnetic solitons are ideal to use for logical operations, and we demonstrate the functionality of a three- input majority gate, in which the input states can be controlled by applying an external electromagnetic field or spin-polarized currents. One of the main advantages of the proposed device is that the input and output signals are encoded in the chirality of solitons, that may be moved, allowing to perform logical operations using only minute electric currents. As an example we illustrate how the three input majority gate can be used to perform logical relations, such as Boolean AND and OR.

  • 13.
    Lüder, Johann
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden; Department of Mechanical Engineering, National University, Singapore, Singapore.
    Schött, Johan
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Brena, Barbara
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Haverkort, Maurits W.
    Institute for Theoretical Physics, Heidelberg University, Heidelberg, Germany.
    Thunström, Patrik
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Sanyal, Biplab
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Di Marco, Igor
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Kvashnin, Yaroslav O.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Theory of L-edge spectroscopy of strongly correlated systems2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245131Article in journal (Refereed)
    Abstract [en]

    X-ray absorption spectroscopy measured at the L edge of transition metals (TMs) is a powerful element selective tool providing direct information about the correlation effects in the 3d states. The theoretical modeling of the 2p -> 3d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012)]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.

  • 14.
    Nieves, P.
    et al.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, Universidad de Burgos, Burgos, Spain.
    Arapan, S.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, Universidad de Burgos, Burgos, Spain; VSB Tech Univ Ostrava, IT4Innovations, Ostrava, Czech Republic.
    Maudes-Raedo, J.
    Department of Civil Engineering, Universidad de Burgos, Burgos, Spain.
    Marticorena-Sánchez, R.
    Department of Civil Engineering, Universidad de Burgos, Burgos, Spain.
    Del Brio, N. L.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, Universidad de Burgos, Burgos, Spain.
    Kovacs, A.
    Department for Integrated Sensor Systems, Danube University Krems, Lower Austria, Krems, Austria.
    Echevarria-Bonet, C.
    BCMaterials, Basque Centre for Materials, Applications and Nanostructures, UPV/EHU Science Park, Leioa, Spain.
    Salazar, D.
    BCMaterials, Basque Centre for Materials, Applications and Nanostructures, UPV/EHU Science Park, Leioa, Spain.
    Weischenberg, J.
    Department of Materials and Geosciences, TU Darmstadt, Darmstadt, Germany.
    Zhang, H.
    Department of Materials and Geosciences, TU Darmstadt, Darmstadt, Germany.
    Vekilova, O. Yu
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Serrano-Lopez, R.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, Universidad de Burgos, Burgos, Spain.
    Barandiaran, J. M.
    BCMaterials, Basque Centre for Materials, Applications and Nanostructures, UPV/EHU Science Park, Leioa, Spain.
    Skokov, K.
    Department of Materials and Geosciences, TU Darmstadt, Darmstadt, Germany.
    Gutfleisch, O.
    Department of Materials and Geosciences, TU Darmstadt, Darmstadt, Germany.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Herper, H. C.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Schrefl, T.
    Department for Integrated Sensor Systems, Danube University Krems, Lower Austria, Krems, Austria.
    Cuesta-López, S.
    ICCRAM, International Research Center in Critical Raw Materials and Advanced Industrial Technologies, Universidad de Burgos, Burgos, Spain.
    Database of novel magnetic materials for high-performance permanent magnet development2019In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 168, p. 188-202Article in journal (Refereed)
    Abstract [en]

    This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database.

  • 15.
    Pal, Somnath
    et al.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Jana, Somnath
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Govinda, Sharada
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Pal, Banabir
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Mukherjee, Sumanta
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Keshavarz, Samara
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Thonig, Danny
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Kvashnin, Yaroslav
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Mathieu, Roland
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Nordblad, Per
    Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
    Freeland, John W.
    Argonne National Laboratory, Argonne Illinois, USA.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Karis, Olof
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Sarma, D. D.
    Solid State and Structural Chemistry Unit, Indian Institute of Science, Bengaluru, India.
    Peculiar magnetic states in the double perovskite Nd2NiMnO62019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 4, article id 045122Article in journal (Refereed)
    Abstract [en]

    We present magnetic measurements on Nd2NiMnO6 which exhibits a well-known insulating paramagnetic state to an insulating ferromagnetic state transition when cooled below 200 K. Beyond this basic fact, there is a great deal of diversity in the reported magnetic properties and interpretation of specific anomalies observed in the magnetic data of this compound below the Curie temperature. We address specifically two anomalies discussed in the past, namely, a spin-glass like behavior observed in some samples near 100 K and a downturn in the magnetization with a lowering of the temperature below approximately 50 K. We show for the first time that the application of an increasing magnetic field can systematically change the low-temperature behavior to make the down-turn in the magnetization into an upturn. With the help of first principle calculations and extensive simulations along with our experimental observations, we provide a microscopic understanding of all magnetic properties observed in this interesting system to point out that the glassiness around 100 K is absent in well-ordered samples and that the low-temperature magnetic anomaly below 50 K is a consequence of a ferromagnetic coupling of the Nd spin moments with the spin of the Ni-Mn ordered sublattice without giving rise to any ordering of the Nd sublattice that remains paramagnetic, contrary to earlier claims. We explain this counter-intuitive interpretation of a ferromagnetic coupling of Nd spins with Ni-Mn spin giving rise to a decrease in the total magnetic moment by noting the less than half-filled 4f occupation of Nd that ensures orbital and spin moments of Nd to be opposite to each other due to the spin-orbit coupling. Since the ground state total magnetic moment of Nd has a contribution from the orbital moment, that is larger than the spin moment, the total moment of Nd is indeed pointing in a direction opposite to the direction of spin moments of the Ni-Mn sublattice as a consequence of the ferromagnetic exchange coupling between Nd and Ni-Mn spins.

  • 16.
    Pervishko, Anastasiia A.
    et al.
    ITMO University, Saint Petersburg, Russia.
    Baglai, Mikhail I.
    ITMO University, Saint Petersburg, Russia; Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Yudin, Dmitry
    ITMO University, Saint Petersburg, Russia.
    Another view on Gilbert damping in two-dimensional ferromagnets2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 17148Article in journal (Refereed)
    Abstract [en]

    A keen interest towards technological implications of spin-orbit driven magnetization dynamics requests a proper theoretical description, especially in the context of a microscopic framework, to be developed. Indeed, magnetization dynamics is so far approached within Landau-Lifshitz-Gilbert equation which characterizes torques on magnetization on purely phenomenological grounds. Particularly, spin-orbit coupling does not respect spin conservation, leading thus to angular momentum transfer to lattice and damping as a result. This mechanism is accounted by the Gilbert damping torque which describes relaxation of the magnetization to equilibrium. In this study we work out a microscopic Kubo-Streda formula for the components of the Gilbert damping tensor and apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the weak disorder limit. We show that an exact analytical expression corresponding to the Gilbert damping parameter manifests linear dependence on the scattering rate and retains the constant value up to room temperature when no vibrational degrees of freedom are present in the system. We argue that the methodology developed in this paper can be safely applied to bilayers made of non- and ferromagnetic metals, e.g., CoPt.

  • 17.
    Schmitz-Antoniak, Carolin
    et al.
    Peter-Grünberg-Institut (PGI-6), Forschungszentrum Jülich, Jülich, Germany.
    Schmitz, Detlef
    Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany.
    Warland, Anne
    Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Duisburg, Germany.
    Darbandi, Masih
    Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Duisburg, Germany; Chemistry faculty, University of Tabriz, Tabriz, Iran.
    Haldar, Soumyajyoti
    Institute of Theoretical Physics & Astrophysics, University of Kiel, Kiel, Germany.
    Bhandary, Sumanta
    Centre de Physique Théorique (CPHT), Ecole Polytechnique, Palaiseau cedex, France.
    Sanyal, Biplab
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology.
    Wende, Heiko
    Fak Phys, Univ Duisburg Essen, Duisburg, Germany; Ctr Nanointegrat Duisburg Essen CENIDE, Univ Duisburg Essen, Duisburg, Germany.
    Suppression of the Verwey Transition by Charge Trapping2018In: Annalen der Physik, ISSN 0003-3804, E-ISSN 1521-3889, Vol. 530, no 3, article id 1700363Article in journal (Refereed)
    Abstract [en]

    The Verwey transition in Fe3O4 nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO2. By X-ray absorption spectroscopy and its associated X-ray magnetic circular dichroism this suppression can be correlated to localized Fe2+ states and a reduced double exchange visible in different site-specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe3O4/ SiO2 interface and the consequent difficulties in the formation of the common phases of Fe3O4. By comparison to X-ray absorption spectra of bare Fe3O4 nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations.

  • 18.
    Shaw, Justin M.
    et al.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Delczeg-Czirjak, Erna K.
    Department of Physics and Astronomy, University Uppsala, Uppsala, Sweden.
    Edwards, Eric R. J.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Kvashnin, Yaroslav
    Department of Physics and Astronomy, University Uppsala, Uppsala, Sweden.
    Thonig, Danny
    Department of Physics and Astronomy, University Uppsala, Uppsala, Sweden.
    Schoen, Martin A. W.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States; Department of Physics, University of Regensburg, Regensburg, Germany.
    Pufall, Matt
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Schneider, Michael L.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Silva, Thomas J.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Karis, Olof
    Department of Physics and Astronomy, University Uppsala, Uppsala, Sweden.
    Rice, Katherine P.
    CAMECA Instruments, Madison WI, United States.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, University Uppsala, Uppsala, Sweden.
    Nembach, Hans T.
    Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder CO, United States.
    Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders: Experiment and theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094420Article in journal (Refereed)
    Abstract [en]

    We show that very low values of the magnetic damping parameter can be achieved in sputter deposited polycrystalline films of Co2MnGe annealed at relatively low temperatures ranging from 240 degrees C to 400 degrees C. Damping values as low as 0.0014 are obtained with an intrinsic value of 0.0010 after spin-pumping contributions are considered. Of importance to most applications is the low value of inhomogeneous linewidth that yields measured linewidths of 1.8 and 5.1 mT at 10 and 40 GHz, respectively. The damping parameter monotonically decreases as the B2 order of the films increases. This trend is reproduced and explained by ab initio calculations of the electronic structure and damping parameter. Here, the damping parameter is calculated as the structure evolves from A2 to B2 to L2(1) orders. The largest decrease in the damping parameter occurs during the A2 to B2 transition as the half-metallic phase becomes established.

  • 19.
    Shirinyan, Albert A.
    et al.
    ITMO University, Saint-Petersburg, Russian Federation.
    Kozin, Valerii K.
    ITMO University, Saint-Petersburg, Russian Federation; Science Institute, University of Iceland, Reykjavik, Iceland.
    Hellsvik, Johan
    Nordita, Stockholm, Sweden; Department of Physics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Pereiro, Manuel
    Department of Physics and Astronomy, Materials Theory Division, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Materials Theory Division, Uppsala University, Uppsala, Sweden.
    Yudin, Dmitry
    Deep Quantum Labs, Skolkovo Institute of Science and Technology, Moscow, Russian Federation.
    Self-organizing maps as a method for detecting phase transitions and phase identification2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 4, article id 041108Article in journal (Refereed)
    Abstract [en]

    Originating from image recognition, methods of machine learning allow for effective feature extraction and dimensionality reduction in multidimensional datasets, thereby providing an extraordinary tool to deal with classical and quantum models in many-body physics. In this study, we employ a specific unsupervised machine learning technique-self-organizing maps-to create a low-dimensional representation of microscopic states, relevant for macroscopic phase identification and detecting phase transitions. We explore the properties of spin Hamiltonians of two archetype model systems: a two-dimensional Heisenberg ferromagnet and a three-dimensional crystal, Fe in the body-centered-cubic structure. The method of self-organizing maps, which is known to conserve connectivity of the initial dataset, is compared to the cumulant method theory and is shown to be as accurate while being computationally more efficient in determining a phase transition temperature. We argue that the method proposed here can be applied to explore a broad class of second-order phase-transition systems, not only magnetic systems but also, for example, order-disorder transitions in alloys.

  • 20.
    Szilva, A.
    et al.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Thonig, D.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Bessarab, P. F.
    Science Institute, University of Iceland, Reykjavik, Iceland; Department of Nanophotonics and Metamaterials, ITMO University, St. Petersburg, Russia.
    Kvashnin, Y. O.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Rodrigues, D. C. M.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Faculdade de Física, Universidade Federal do Pará, Belém, Brazil.
    Cardias, R.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Faculdade de Física, Universidade Federal do Pará, Belém, Brazil.
    Pereiro, M.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Nordström, L.
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Bergman, A.
    Maison de la Simulation, USR 3441, CEA-CNRS-INRIA-Université Paris-Sud-Université de Versailles, Gif-sur-Yvette, France; Institut Nanosciences et Cryogénie (Inac) and Modeling and Exploration of Materials (MEM), Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), Grenoble, France.
    Klautau, A. B.
    Faculdade de Física, Universidade Federal do Pará, Belém, Brazil.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Theory of noncollinear interactions beyond Heisenberg exchange: Applications to bcc Fe2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 14, article id 144413Article in journal (Refereed)
    Abstract [en]

    We show for a simple noncollinear configuration of the atomistic spins (in particular, where one spin is rotated by a finite angle in a ferromagnetic background) that the pairwise energy variation computed in terms of multiple-scattering formalism cannot be fully mapped onto a bilinear Heisenberg spin model even in the absence of spin-orbit coupling. The non-Heisenberg terms induced by the spin-polarized host appear in leading orders in the expansion of the infinitesimal angle variations. However, an E-g - T-2g symmetry analysis based on the orbital decomposition of the exchange parameters in bcc Fe leads to the conclusion that the nearest-neighbor exchange parameters related to the T-2g orbitals are essentially Heisenberg-like: they do not depend on the spin configuration, and can, in this case, be mapped onto a Heisenberg spin model even in extreme noncollinear cases.

  • 21.
    Thonig, Danny
    et al.
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Kvashnin, Yaroslav
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Pereiro, Manuel
    Department of Physics and Astronomy, Materials Theory, Uppsala University, Uppsala, Sweden.
    Nonlocal Gilbert damping tensor within the torque-torque correlation model2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 1, article id 013801Article in journal (Refereed)
    Abstract [en]

    An essential property of magnetic devices is the relaxation rate in magnetic switching, which depends strongly on the damping in the magnetization dynamics. It was recently measured that damping depends on the magnetic texture and, consequently, is a nonlocal quantity. The damping enters the Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping parameter a, which does not, in a straightforward formulation, account for nonlocality. Efforts were spent recently to obtain Gilbert damping from first principles for magnons of wave vector q. However, to the best of our knowledge, there is no report about real-space nonlocal Gilbert damping aij. Here, a torque-torque correlation model based on a tight-binding approach is applied to the bulk elemental itinerant magnets and it predicts significant off-site Gilbert damping contributions, which could be also negative. Supported by atomistic magnetization dynamics simulations, we reveal the importance of the nonlocal Gilbert damping in atomistic magnetization dynamics. This study gives a deeper understanding of the dynamics of the magnetic moments and dissipation processes in real magnetic materials. Ways of manipulating nonlocal damping are explored, either by temperature, materials doping, or strain.

  • 22.
    Tian, Li-Yun
    et al.
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Levämäki, Henrik
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Kokko, Kalevi
    Department of Physics and Astronomy, University of Turku, Turku, Finland; Turku University Centre for Materials and Surfaces (MatSurf), Turku, Finland.
    Nagy, Ágnes
    Department of Theoretical Physics, University of Debrecen, Debrecen, Hungary.
    Délczeg-Czirják, Erna Krisztina
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Vitos, Levente
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden; Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Budapest, Hungary.
    Density Functional Theory description of the order-disorder transformation in Fe-Ni2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 8172Article in journal (Refereed)
    Abstract [en]

    The thermodynamic ordering transformation of tetragonal FeNi system is investigated by the Exact Muffin-Tin Orbitals (EMTO) method. The tetragonal distortion of the unit cell is taken into account and the free energy is calculated as a function of long-range order and includes the configurational, vibrational, electronic and magnetic contributions. We find that both configurational and vibrational effects are important and that the vibrational effect lowers the predicted transformation temperature by about 480 K compared to the value obtained merely from the configurational free energy. The predicted temperature is in excellent agreement with the experimental value when all contributions are taken into account. We also perform spin dynamics calculations for the magnetic transition temperature and find it to be in agreement with the experiments. The present research opens new opportunities for quantum-mechanical engineering of the chemical and magnetic ordering in tetrataenite.

  • 23.
    Vekilova, Olga Yu
    et al.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Fayyazi, Bahar
    Materials Science, TU Darmstadt, Darmstadt, Germany.
    Skokov, Konstantin P.
    Materials Science, TU Darmstadt, Darmstadt, Germany.
    Gutfleisch, Oliver
    Materials Science, TU Darmstadt, Darmstadt, Germany.
    Echevarria-Bonet, Cristina
    BCMaterials, UPV/EHU Science Park, Leioa, Spain.
    Barandiarán, Jose Manuel
    BCMaterials, UPV/EHU Science Park, Leioa, Spain.
    Kovacs, Alexander
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Fischbacher, Johann
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Schrefl, Thomas
    Department for Integrated Sensor Systems, Danube University Krems, Wiener Neustadt, Austria.
    Eriksson, Olle
    Örebro University, School of Science and Technology. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Herper, Heike C.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Tuning the magnetocrystalline anisotropy of Fe3Sn by alloying2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 2, article id 024421Article in journal (Refereed)
    Abstract [en]

    The electronic structure, magnetic properties, and phase formation of hexagonal ferromagnetic Fe3Sn-based alloys have been studied from first principles and by experiment. The pristine Fe3Sn compound is known to fulfill all the requirements for a good permanent magnet, except for the magnetocrystalline anisotropy energy (MAE). The latter is large, but planar, i.e., the easy magnetization axis is not along the hexagonal c direction, whereas a good permanent magnet requires the MAE to be uniaxial. Here we consider Fe3Sn0.75M0.25, where M = Si, P, Ga, Ge, As, Se, In, Sb, Te, Pb, and Bi, and show how different dopants affect the MAE and can alter it from planar to uniaxial. The stability of the doped Fe3Sn phases is elucidated theoretically via the calculations of their formation enthalpies. A micromagnetic model is developed to estimate the energy density product (BH)(max) and coercive field mu H-0(c) of a potential magnet made of Fe3Sn0.75M0.25, the most promising candidate from theoretical studies. The phase stability and magnetic properties of the Fe3Sn compound doped with Sb and Mn have been checked experimentally on the samples synthesised using the reactive crucible melting technique as well as by solid state reaction. The Fe3Sn-Sb compound is found to be stable when alloyed with Mn. It is shown that even small structural changes, such as a change of the c/a ratio or volume, that can be induced by, e.g., alloying with Mn, can influence anisotropy and reverse it from planar to uniaxial and back.

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