Local electronic structure of Cr in the II–VI diluted ferromagnetic semiconductor Zn_1-xCr_xTe

The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn_1-xCr_xTe (x=0.03 and 0.15) thin films has been investigated using x-ray magnetic circular dichroism (XMCD) and photoemission spectroscopy (PES). Magnetic-field (H) and temperature (T) dependences of the Cr 2p XMCD spectra correspond well to the magnetization measured by a SQUID magnetometer. The line shape of the Cr 2p XMCD spectra is independent of H, T and x, indicating that the ferromagnetism originated from the same electronic states of the Cr ion. A cluster-model analysis indicates that although there are two or more kinds of Cr ions in the Zn_1-xCr_xTe samples, the ferromagnetic XMCD signal originated from Cr ions substituted for the Zn site. The Cr 3d partial density of states extracted using Cr 2p→3d resonant PES shows a broad feature near the top of the valence band, suggesting strong s,p–d hybridization. No density of states is detected at the Fermi level, consistent with their insulating behavior. Based on these findings, we conclude that the double-exchange mechanism cannot explain the ferromagnetism in Zn_{1- x}Cr_xTe.