Uniaxial magnetic anisotropy in amorphous CoFeB films on different orientation GaAs substrates

Since the magnetic anisotropy of ferromagnetic (FM) films on semiconductor substrates has promising application for spintronics, it has stimulated extensive studies in the last two decades [1]. Remarkably, amorphous FM alloy films also exhibit uniaxial magnetic anisotropy (UMA) in the film plane when deposited on semiconductor substrates, e.g. CoFeB/GaAs (001) [2]. Although several models, including `bond-orientational anisotropy´ (BOA) model [2, 3] and random anisotropy model [4], have been proposed to explain the origin of UMA, the underlying mechanism has remained unclear yet. Considering that different cleavage plane of GaAs may have different inter-facial interaction with CoFeB film, a systematic investigation has been performed on the in-plane magnetic anisotropy of the CoFeB films deposited on different orientational GaAs substrates. Co₅₆Fe₂₄B₂₀ (CoFeB) films were deposited respectively on GaAs (001), GaAs (110) and GaAs (111) substrates by d.c. magnetron sputtering at room temperature. Before film growth, the surface contamination and oxides on the GaAs substrate should be removed by a standard procedure similar to that described in Ref. [5]. The base pressure was lower than 8.0×10^-6 Pa and the Ar pressure was kept at 0.3 Pa during film deposition. A Ta film with 2 nm was deposited as capping layer to prevent the CoFeB film from oxidation. The magnetic hysteresis (M-H) loops were measured by a SQUID-VSM (Quantum Design). The angular dependence of M-H loop was measured by a vector VSM (Microsense EV7), from which the magnetic moment parallel (M_x) and perpendicular (M_y) to the field direction can be recorded simultaneously. All the measurements were performed in the film plane at room temperature.