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Fermi Surface Manipulation by External Magnetic Field Demonstrated for a Prototypical Ferromagnet

E. Młyńczak, M. Eschbach, S. Borek, J. Minár, J. Braun, I. Aguilera, G. Bihlmayer, S. Döring, M. Gehlmann, P. Gospodarič, S. Suga, L. Plucinski, S. Blügel, H. Ebert, and C. M. Schneider
Phys. Rev. X 6, 041048 – Published 9 December 2016

Abstract

We consider the details of the near-surface electronic band structure of a prototypical ferromagnet, Fe(001). Using high-resolution angle-resolved photoemission spectroscopy, we demonstrate openings of the spin-orbit-induced electronic band gaps near the Fermi level. The band gaps, and thus the Fermi surface, can be manipulated by changing the remanent magnetization direction. The effect is of the order of ΔE=100meV and Δk=0.1Å1. We show that the observed dispersions are dominated by the bulk band structure. First-principles calculations and one-step photoemission calculations suggest that the effect is related to changes in the electronic ground state and not caused by the photoemission process itself. The symmetry of the effect indicates that the observed electronic bulk states are influenced by the presence of the surface, which might be understood as related to a Rashba-type effect. By pinpointing the regions in the electronic band structure where the switchable band gaps occur, we demonstrate the significance of spin-orbit interaction even for elements as light as 3d ferromagnets. These results set a new paradigm for the investigations of spin-orbit effects in the spintronic materials. The same methodology could be used in the bottom-up design of the devices based on the switching of spin-orbit gaps such as electric-field control of magnetic anisotropy or tunneling anisotropic magnetoresistance.

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  • Received 1 May 2016

DOI:https://doi.org/10.1103/PhysRevX.6.041048

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

E. Młyńczak1,2,*, M. Eschbach1, S. Borek3, J. Minár3,4, J. Braun3, I. Aguilera1, G. Bihlmayer1, S. Döring1, M. Gehlmann1, P. Gospodarič1, S. Suga1,5, L. Plucinski1, S. Blügel1, H. Ebert3, and C. M. Schneider1

  • 1Peter Grünberg Institut PGI, Forschungszentrum Jülich and JARA- Fundamentals of Future Information Technologies, 52425 Jülich, Germany
  • 2Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland
  • 3Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377 München, Germany
  • 4New Technologies-Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic
  • 5Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan

  • *e.mlynczak@fz-juelich.de

Popular Summary

The behavior of electrons in a solid is encoded in the electronic band structure, which links the energy and wave vectors of the electrons. Theoretical calculations predict that the electronic band structure of elemental ferromagnets possesses subtle signatures of a relativistic interaction between the spin of the electrons and the magnetic moment related to their orbital motion, which is referred to as a “spin-orbit coupling.” Up until now, spin-orbit coupling has often been neglected in the analysis of the electronic properties of iron, cobalt, or nickel because of the relatively small energy scale of this interaction (100 meV). However, the existence of spin-orbit coupling has dramatic consequences on the magnetic properties of solids, resulting in effects such as magnetocrystalline anisotropy or spin-dependent transport, which are essential for many technological applications. Here, we examine the momentum-resolved details of the electronic band structure of iron using high-resolution spectroscopy.

We consider thin films of iron grown on gold and maintained at 50 K. After magnetizing the iron samples, we use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic signatures of iron’s spin-orbit coupling. We successfully identify the regions of the Brillouin zone where spin-orbit coupling-induced band gaps are formed. Additionally, we show that these band gaps can be opened or closed depending on the direction of the applied magnetic field. We demonstrate that first-principles calculations are consistent with our experimental findings, and we conclude that spin-orbit coupling cannot be neglected even in relatively light elements such as 3d ferromagnets.

We expect that our results will motivate new investigations of spin-orbit effects in spintronic materials.

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Vol. 6, Iss. 4 — October - December 2016

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