Unusual perpendicular anisotropy in Co₂TiSi films

Authors

Yunlong Jin, University of Nebraska-LincolnFollow
Shah R. Valloppilly, University of Nebraska-LincolnFollow
Parashu R. Kharel, South Dakota State UniversityFollow
Rohit Pathak, Indian Institute of Technology Mandi
Arti Kashyap, Indian Institute of TechnologyFollow
Ralph Skomski, University of Nebraska - LincolnFollow
David J. Sellmyer, University of Nebraska-LincolnFollow

ORCID IDs

Yunlong Jin, https://orcid.org/0000-0003-1946-8474

Date of this Version

2019

Citation

Published in Journal of Physics D: Applied Physics 52 (2019), 035001

doi 10.1088/1361-6463/aae80f

Comments

Copyright © 2018 IOP Publishing Ltd. Used by permission.

Abstract

Thin films of Co₂TiSi on MgO are investigated experimentally and theoretically. The films were produced by magnetron sputtering on MgO(001) and have a thickness of about 100 nm. As bulk Co₂TiSi, they crystallize in the normal cubic Heusler (L2₁) structure, but the films are slightly distorted (c/a = 1.0014) and contain some antisite disorder. The films exhibit a robust perpendicular anisotropy of 0.5 MJ m⁻³. This result is surprising for several reasons. First, surface and interface anisotropies are too small to explain perpendicular anisotropy in such rather thick films. Second, Co₂TiSi has a substantial magnetization and crystallizes in a cubic Heusler structure, so that conventional wisdom predicts a preferential magnetization direction in the film plane rather than perpendicular. Third, the lattice strain of 0.14% is unable to account for the perpendicular anisotropy. We explain the perpendicular anisotropy as a quasicubic symmetry breaking chemical-ordering effect promoted by the substrate.