Magnetic anisotropy switching in heavily-Fe-doped high-Curie-temperature ferromagnetic semiconductor (Ga0.7, Fe0.3)Sb with a critical thickness

Ferromagnetic semiconductor (FMSs), which exhibits both magnetic and semiconducting properties, are promising for semiconductor-based spintronics devices. Magnetic anisotropy (MA) plays an important role in determining the magnetization direction of ferromagnetic materials. Here, we present the thickness-dependence control of MA in (Ga 0.7 , Fe 0.3 )Sb by growing samples with different thicknesses $d=20-55\ \text{nm}$ grown on AlSb by low-temperature molecular beam epitaxy. We used ferromagnetic resonance (FMR) to estimate the MA constants of the (Ga 0.7 , Fe 0.3 )Sb. We systematically measured the dependence of the FMR resonance field on the external magnetic-field direction and fitted a theoretical curve to obtain the MA fields of the (Ga, Fe)Sb thin films, and obtained the effective MA constants ( $K_{\text{eff}}$ ) of (Ga, Fe)Sb. From the sign of $K_{\text{eff}}$ , we found that MA changes from in-plane magnetic anisotropy (IMA) to perpendicular magnetic anisotropy (PMA) with increasing $d$ . To understand this, we separated the $K_{\text{eff}}$ into the volume contribution ( $K_{\mathrm{V}}$ ) and the interface contribution ( $K_{\mathrm{I}}$ ). We show that the IMA originates from the film interface due to the tensile strain when the films are thin, whereas $K_{\mathrm{V}}$ causes PMA in (Ga, Fe)Sb. The observation of FMR at room temperature and control of MA are important steps towards device applications of (Ga, Fe)Sb.