Interface Induced Uniaxial Magnetic Anisotropy in Amorphous CoFeB Films on AlGaAs(001)

We demonstrate an isolated magnetic interface anisotropy in amorphous CoFeB films on (Al)GaAs(001), similar to that in epitaxial films but without a magnetocrystalline anisotropy term. The direction of the easy axis corresponds to that due to the interfacial interaction proposed for epitaxial films. We show that the anisotropy is determined by the relative orbital component of the atomic magnetic moments. Charge transfer is ruled out as the origin of the interface anisotropy, and it is postulated that the spin-orbit interaction in the semiconductor is crucial in determining the magnetic anisotropy.

Figure 1

Room temperature MOKE hysteresis loops of $\mathrm{AlGaAs}/\mathrm{GaAs}/\mathrm{CoFeB}[35\AA ]$, (a),(b), and $\mathrm{AlGaAs}/\mathrm{CoFeB}[35\AA ]$, (c),(d), contacts. The field is applied parallel or perpendicular to the deposition field, as indicated. The solid line in frame (a) is a fit using the Stoner-Wohlfarth model described in the main text.

Figure 2

Cross-sectional HRTEM micrographs of the same $\mathrm{AlGaAs}/\mathrm{GaAs}/\mathrm{CoFeB}$, (a),(b), and $\mathrm{AlGaAs}/\mathrm{CoFeB}$, (c),(d), contacts. The growth field direction and uniaxial magnetic anisotropy axes are indicated in each frame. The corrugation period $\xi$ and amplitude Δ are indicated in frame (b).

Figure 3

SXMCD difference spectra across the Co (main) and Fe (inset) $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ absorption edges for the same CoFeB [35 Å] films deposited on (a) $\mathrm{AlGaAs}/\mathrm{GaAs}$ or (b) AlGaAs epilayers. For both elements, the insertion of a GaAs interface layer results in an increase in the ratio of orbital to spin magnetic moments, increasing the relative $L_{\mathrm{III}}:L_{\mathrm{II}}$ dichroism. The upper inset to frame (b) shows the SXMCD measurement geometry schematically.