Stoichiometry dependent phase transition in Mn-Co-Ga-based thin films: From cubic in-plane, soft magnetized to tetragonal perpendicular, hard magnetized

摘要

Epitaxial thin films of Mn_3-xCo_xGa were grown on MgO by magnetron co-sputtering with different Co content. Dependent on the Co content tetragonal or cubic structures are obtained. The composition dependence of saturation magnetization M_S and uniaxial magnetic anisotropy K_u in the epitaxial films were investigated. A high magnetic anisotropy K_u of 1.2 MJ m-3 was achieved for the Mn_2.6Co_0.3Ga_1.1 film with low magnetic moment of 0.84 μ_B. The valence band spectra of the films were investigated mainly by hard x-ray photoelectron spectroscopy. The evidence of sharp states in the cubic case, which are smeared out in the tetragonal case, proof the existence of a van Hove singularity that causes a band Jahn-Teller effect accompanied by a tetragonal distortion. These differences are in well agreement to the ab-initio calculations of the electronic structure.