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  • 1.
    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.

  • 2.
    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.

  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    Shao, Lei
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Andrén, Daniel
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Jones, Steven
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Optically controlled stochastic jumps of individual gold nanorod rotary motors2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 8, article id 085404Article in journal (Refereed)
    Abstract [en]

    Brownian microparticles diffusing in optical potential-energy landscapes constitute a generic test bed for nonequilibrium statistical thermodynamics and have been used to emulate a wide variety of physical systems, ranging from Josephson junctions to Carnot engines. Here we demonstrate that it is possible to scale down this approach to nanometric length scales by constructing a tilted washboard potential for the rotation of plasmonic gold nanorods. The potential depth and tilt can be precisely adjusted by modulating the light polarization. This allo`ws for a gradual transition from continuous rotation to discrete stochastic jumps, which are found to follow Kramers dynamics in excellent agreement with stochastic simulations. The results widen the possibilities for fundamental experiments in statistical physics and provide insights into how to construct light-driven nanomachines and multifunctional sensing elements.

  • 8.
    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.

  • 9.
    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.

  • 10.
    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.

  • 11.
    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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Output format
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  • asciidoc
  • rtf