Origin of uniaxial magnetic anisotropy in epitaxial InMnAs thin films

The in-plane magnetic anisotropy of (001) oriented InMnAs epitaxial films grown on InAs and GaSb were measured by magnetometry and the longitudinal magneto-optic Kerr effect. InMnAs epitaxial layers when grown on InAs exhibit a significant in-plane uniaxial anisotropy field of -0.66 kG at room temperature. The uniaxial magnetic anisotropy is attributed to differences in Mn atomic density along the [110] and [1- 10] directions, resulting from the uniaxial surface symmetry of the InAs (001) surface. The asymmetry of the Mn density is preserved in InMnAs films grown on InAs by a two-dimensional growth mechanism. However, disorder as evidenced by increasing surface pitting perturbs the growth from an ideal layer-by-layer mechanism. This results in a decrease in the magnitude of the uniaxial anisotropy field with increasing thickness between 320-630 nm. In contrast, InMnAs films grown on GaSb are magnetically isotropic for a thickness range of 50-420 nm. The isotropic behavior is attributed to three-dimensional island growth of films grown on GaSb that eliminates long range order.