  Fe-doped III-V ferromagnetic semiconductor (FMS) (In,Fe)Sb is a promising
material for spintronic device applications because of the n-type carrier
conduction and the ferromagnetism with high Curie temperature (TC > 300 K). To
clarify the mechanism of the high-TC ferromagnetism, we have investigated the
electronic structure and magnetic properties of an (In,Fe)Sb thin film by
performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD) measurements at the Fe L2,3 edges. The magnetic-field
dependence of the XMCD spectra reveals that there are ferromagnetic-like Fe and
paramagnetic-like Fe components in the (In,Fe)Sb thin film. The XAS and XMCD
spectra of the ferromagnetic-like and paramagnetic-like Fe components resemble
those of other Fe-doped FMSs and extrinsic oxides, respectively. The finite
value of the ratio between the orbital and spin magnetic moments estimated by
applying the XMCD sum rules indicates that the valence state of the Fe ions
substituting for the In sites in (In,Fe)Sb is not purely ionic Fe3+, but
intermediate between Fe3+ and Fe2+. The qualitative correspondence between the
magnetic-field dependence of the visible-light magnetic circular dichroism
intensity and that of the XMCD intensity demonstrates that the Zeeman splitting
of the InSb band is proportional to the net magnetization of the doped Fe.
These results suggest that the ferromagnetism of (In,Fe)Sb originates from the
Fe 3d orbitals hybridized with the host InSb bands.
