Magnetism of epitaxial Mn1−xNixAs films on GaAs(001)

We have studied the magnetic, magneto-optic, and structural properties of Mn1−xNixAs films grown by molecular beam epitaxy on GaAs(001). The compositions are x=0.1, 0.2, 0.3 with a thickness about 100 nm. In the magneto-optical Kerr effect, Mn0.9Ni0.1As displays distinct longitudinal and polar Kerr rotations. At x=0.2, the effects are smaller, and are undetectable at x=0.3. Magnetometry yields a linear dependence of magnetization on Ni concentration. X-ray diffraction shows a gradual transition from hexagonal to orthorhombic structure. In contrast, bulk Mn1−xNixAs alloys at 300 K are paramagnetic and orthorhombic for x>0.02 and transform to an hexagonal phase at x=0.22.