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) (G a_0.7,F e_0.3 )Sb layer with a high Curie temperature (T_C>320 K), using ferromagnetic resonance at room temperature. We show that the total MA energy (E_⊥) along the [001] direction changes its sign from positive (in-plane) to negative (perpendicular) with increasing d above an effective critical value d_C^*∼42 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 <001 > 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 <100 > axes. This work provides an important guide for controlling the easy magnetization axis of high-T_C FMS (Ga,Fe)Sb for room-temperature device applications.