Evolution of Fe 3 impurity band state as the origin of high Curie temperature in the -type ferromagnetic semiconductor (Ga,Fe)Sb

Takeda, Takahito*; Sakamoto, Shoya*; Araki, Kosei*; Fujisawa, Yuita*; Anh, L. D.*; Tu, N. T.*; Takeda, Yukiharu   ; Fujimori, Shinichi   ; Fujimori, Atsushi*; Tanaka, Masaaki*; Kobayashi, Masaki*

(Ga,Fe)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature (Tc) is above 300 K when the Fe concentration is equal to or higher than 0.20. However, the origin of the high Tc in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the x dependence of the Fe 3 states in (Ga,Fe)Sb ( = 0.05, 0.15, and 0.25) thin films. The observed Fe 2-3 RPES spectra reveal that the Fe-3 impurity band (IB) crossing the Fermi level becomes broader with increasing , which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3 partial density of states and the first-principles calculations suggests that the Fe-3 IB originates from the minority-spin () states. The results indicate that enhancement of the double-exchange interaction between electrons with increasing is the origin of the high Tc in (Ga,Fe)Sb.