Perpendicularly magnetized Mn-Co-Ga-based thin films with high coercive field

Mn${}_{3-x}$Co${}_x$Ga epitaxial thin films were grown on MgO substrates by magnetron co-sputtering. Structures were tetragonal or cubic depending on Co content. Composition dependence of saturation magnetization and uniaxial magnetic anisotropy $K_u$ of the films were investigated. A high $K_u$ (1.2 MJ m${}^{-3}$) was achieved for the Mn${}_{2.6}$Co${}_{0.3}$Ga${}_{1.1}$ film with the magnetic moment 0.84${\mu }_B$. Valence band spectra were obtained by hard X-ray photoelectron spectroscopy. Sharp peaks in the cubic case, which were absent in the tetragonal case, prove that a van Hove singularity causes a band Jahn-Teller effect with tetragonal distortion. Observations agree well with the first-principles calculations.