Band structure of CuMnAs probed by optical and photoemission spectroscopy

Abstract

Tetragonal phase of CuMnAs progressively appears as one of the key materials for antiferromagnetic spintronics due to efficient current-induced spin-orbit torques whose existence can be directly inferred from crystal symmetry. Theoretical understanding of spintronic phenomena in this material, however, relies on the detailed knowledge of electronic structure (band structure and corresponding wave functions) which has so far been tested only to a limited extent. We show that AC permittivity (obtained from ellipsometry) and UV photoelectron spectra agree with density functional calculations. Together with the x-ray diffraction and precession electron diffraction tomography, our analysis confirms recent theoretical claim [Phys.Rev.B 96, 094406 (2017)] that copper atoms occupy lattice positions in the basal plane of the tetragonal unit cell.Magnetic moments in antiferromagnets have been notoriously difficult to manipulate. With the exception of materials having low Néel temperature and small magnetic anisotropy, very strong magnetic fields must be applied. Such fields would be too strong to be of any practical use and, moreover, they can never be applied as locally as electric pulses. Recently, an alternative manipulation mechanism has been proposed 1 which relies on current-induced spin-orbit torques (SOTs) acting in the bulk of the antiferromagnetic material. They result from a build-up of staggered spin polarisation (i.e. the one which alternates sign on two magnetic sublattices) in response to an applied uniform electric current; such polarisation can be calculated in the framework of linear response to electric field. 2,3 A prediction of sizable SOT in CuMnAs has soon been experimentally confirmed 4 and prototype memories where the writing is done using SOT have been demonstrated. 5 Devices based on thin films of CuMnAs thus claim a prominent role within the fast developing field of antiferromagnetic spintronics. 6,7 Quantitative modelling of SOT (and many other material-specific quantities) relies on a detailed knowledge of the electronic structure. 8 While well-established ab initio methods have been used for this purpose, little effort has so far been dedicated to validating the band structure in terms of comparing calculated and measured spectral properties. 9 We fill this gap by exploring the complex AC permittivity in the optical range and photoemission spectroscopy in the UV range (UPS) and comparing them to density functional theory (DFT) calculations. We find a good agreement between the experimental data and the calculated properties provided the elec-tronic correlations are treated beyond DFT, using Hubbard model characterised by an on-site repulsion U on Mn 3d orbitals. Moreover, we demonstrate that the AC permittivity in the optical range can be used to discern different phases of CuMnAs. Focusing on the tetragonal phase of CuMnAs, 10 we corroborate analysis of our spectral measurements by precession electron diffraction tomography (PEDT), which points to a phase recently claimed to have the lowest ...

3D Electron Diffraction: The Nanocrystallography Revolution

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Precession electron diffraction tomography on twinned crystals: application to CaTiO3thin films

“…Electron diffraction tomography (Kolb et al, 2007(Kolb et al, , 2008Mugnaioli et al, 2009), combined or not with precession electron diffraction (PED) (Vincent & Midgley, 1994), appears to be the ideal technique to investigate the structure of nanomaterials and has already proved its efficiency for solving the structure of unknown materials deposited in the form of thin films (Boullay et al, 2009;Simon et al, 2013;Zhang et al, 2016;Li et al, 2017;Veis et al, 2018). With this technique, the kinematical approximation is a good hypothesis for quantitative analysis of the intensities, and structure solution methods such as the 'charge flipping' algorithm (Palatinus & Chapuis, 2007) can be used.…”

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