Magnetic anisotropy of half-metallic Co2FeAl ultra-thin films epitaxially grown on GaAs(001)

Single crystalline Co2FeAl films with different thicknesses varying from 3.6 to 10.6 nm have been grown on GaAs (001) using Molecule Beam Epitaxy (MBE). The magnetic characteristics were investigated by in-situ magneto-optical Kerr effect (MOKE). For all the samples, the angle dependent magnetization energy has a relatively high and steep peak around [110] direction which is the hard axis, and a wide basin from [110] to [100] which is the range of the easy axis. More interestingly, the magnetic anisotropy includes a strong uniaxial component due to the Co2FeAl/GaAs interface, a cubic one from Co2FeAl crystalline structure, and an unexpected localized anisotropy term around the [110] direction. All the three anisotropy components overlap their own hard axis around [110] direction resulting in a steep energy barrier, which leads to unusual inverted hysteresis loops around [110]. Our findings add a building block for using half-metallic Co2FeAl thin films in the application of magnetic storage devices.