  We report switching of magnetic anisotropy (MA) from in-plane to
perpendicular with increasing the thickness d of a (001)-oriented
ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie
temperature (Tc > 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 \mathrm{d}_\mathrm{C}^\mathrm{*}\ ~ 42 nm. We reveal
that (Ga,Fe)Sb has two-fold symmetry in the film plane. Meanwhile, in the plane
perpendicular to the film including the in-plane [110] axis, the two-fold
symmetry with the easy magnetization axis along [110] changes to four-fold
symmetry with 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 four-fold 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-Tc FMS (Ga,Fe)Sb for
room-temperature device applications.
