Magnetocrystalline anisotropies in (Ga,Mn)As: Systematic theoretical study and comparison with experiment

Abstract

We present a theoretical survey of magnetocrystalline anisotropies in\n(Ga,Mn)As epilayers and compare the calculations to available experimental\ndata. Our model is based on an envelope function description of the valence\nband holes and a spin representation for their kinetic-exchange interaction\nwith localised electrons on Mn ions, treated in the mean-field approximation.\nFor epilayers with growth induced lattice-matching strains we study in-plane to\nout-of-plane easy-axis reorientations as a function of Mn local-moment\nconcentration, hole concentration, and temperature. Next we focus on the\ncompetition of in-plane cubic and uniaxial anisotropies. We add an in-plane\nshear strain to the effective Hamiltonian in order to capture measured data in\nbare, unpatterned epilayers, and we provide microscopic justification for this\napproach. The model is then extended by an in-plane uniaxial strain and used to\ndirectly describe experiments with strains controlled by postgrowth lithography\nor attaching a piezo stressor. The calculated easy-axis directions and\nanisotropy fields are in semiquantitative agreement with experiment in a wide\nparameter range.\n