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

TL;DR

This study investigates the origin of high Curie temperature in (Ga,Fe)Sb by examining Fe 3d states and impurity band evolution, revealing that the broadening of the impurity band and its interaction with electrons drive ferromagnetism.

Contribution

It provides new insights into the Fe 3d impurity band evolution and its role in high-temperature ferromagnetism in (Ga,Fe)Sb using RPES and first-principles calculations.

Findings

Fe 3d impurity band broadens with increasing Fe concentration

Impurity band originates from minority-spin e states

Enhanced e_downarrow electron interaction explains high Curie temperature

Abstract

(Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature ($T_{\rm C}$) is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20. However, the origin of the high $T_{\rm C}$ 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$d$ states in (Ga$_{1-x}$,Fe$_x$)Sb ($x$ = 0.05, 0.15, and 0.25) thin films. The observed Fe 2$p$-3$d$ RPES spectra reveal that the Fe-3$d$ impurity band (IB) crossing the Fermi level becomes broader with increasing $x$, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3$d$ partial density of states and the first-principles calculations suggests that the Fe-3$d$ IB originates from the minority-spin ($\downarrow$) $e$ states. The results indicate that enhancement of the interaction between $e_\downarrow$ electrons with increasing $x$ is the origin of the high $T_{\rm C}$ in (Ga,Fe)Sb.