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

Epitaxial thin films of Mn3-xCoxGa 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 Mn2.6Co0.3Ga1.1 film with low magnetic moment of 0.84 mu(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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770303]