Magnetism of ultrathin FeCo (001) films on GaAs(001)

Epitaxial Fe34Co66 films in a thickness range from 3 to 100 monolayers (MLs ) were grown by molecular beam epitaxy on GaAs(001) at room temperature. Th e growth was characterized by reflection high energy electron diffraction a nd x-ray diffraction. The magnetic properties were investigated by alternat ing gradient magnetometry magneto-optic Kerr effect, and superconducting qu antum interference device magnetometry. The films show a strong interface-i nduced uniaxial in-plane anisotropy with the easy axis along [110]. In addi tion, the fourfold anisotropy coefficient changes sign around 6 ML i.e., th e easy axis of the fourfold anisotropy switches from < 110 > to < 100 > wit h decreasing thickness. (C) 2000 American Institute of Physics. [S0021-8979 (00)31408-6].