In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature

We report switching of magnetic anisotropy (MA) from in-plane to perpendicular with increasing the thickness $d$ of a (001)-oriented ferromagnetic-semiconductor (FMS) $(\mathrm{G}{\mathrm{a}}_{0.7},\mathrm{F}{\mathrm{e}}_{0.3})\mathrm{Sb}$ layer with a high Curie temperature (${T}_{\mathrm{C}}g320$ K), using ferromagnetic resonance at room temperature. We show that the total MA energy (${E}_{\ensuremath{\perp}}$) along the [001] direction changes its sign from positive (in-plane) to negative (perpendicular) with increasing $d$ above an effective critical value ${d}_{\mathrm{C}}^{*}\ensuremath{\sim}42\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. We reveal that (Ga,Fe)Sb has twofold symmetry in the film plane. Meanwhile, in the plane perpendicular to the film including the in-plane [110] axis, the twofold symmetry with the easy magnetization axis along [110] changes to fourfold symmetry with the easy magnetization axis along $\ensuremath{\langle}001\ensuremath{\rangle}$ with increasing $d$. This peculiar behavior is different from that of (Ga,Mn)As, in which only the in-plane MA depends on the film thickness and has fourfold symmetry due to its dominant cubic anisotropy along the $\ensuremath{\langle}100\ensuremath{\rangle}$ axes. This work provides an important guide for controlling the easy magnetization axis of high-${T}_{\mathrm{C}}$ FMS (Ga,Fe)Sb for room-temperature device applications.