Temperature dependence of magnetic anisotropy in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

We study the temperature dependence of magnetic anisotropy (MA) of ferromagnetic semiconductor (Ga-0.7,Fe-0.3)Sb thin films with thicknesses of 20 nm and 40 nm using ferromagnetic resonance. With decreasing temperature from 300 to 10 K, the easy magnetization axis of the 40-nm-thick film changes from in-plane to perpendicular at 250 K, while that of the 20-nm-thick film lies in the film plane at all measurement temperatures (10-300 K). In the 40-nm-thick film, the uniaxial perpendicular anisotropy (K-2 perpendicular to) significantly increases with decreasing temperature and surpasses the thin-film shape anisotropy, leading to perpendicular magnetic anisotropy (PMA). We present a possible scenario that the increase in K-2 perpendicular to originates from the formation of the Fe-rich nanocolumns with the perpendicular shape anisotropy, which induces the PMA in the whole film at low temperatures due to carrier-mediated exchange interactions between Fe spin in the Fe-rich nanocolumns and Fe spin in the (Ga,Fe)Sb matrix. Our findings on the temperature dependence of MA of heavily Fe-doped (Ga,Fe)Sb provide insights into the mechanism of high-Curie-temperature ferromagnetism.