Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor Zn$_{1-x}$Cr$_x$Te

TL;DR

This study investigates the electronic structure of Cr ions in Zn$_{1-x}$Cr$_x$Te thin films, revealing that ferromagnetism originates from Cr ions substituting Zn sites and is driven by strong hybridization, not double exchange.

Contribution

The paper provides detailed spectroscopic analysis showing the origin of ferromagnetism in Cr-doped ZnTe and rules out the double exchange mechanism as the cause.

Findings

Ferromagnetism linked to Cr ions substituting Zn sites.

Cr 3d states show strong hybridization with p and s orbitals.

No states at Fermi level, indicating insulating behavior.

Abstract

The electronic structure of the Cr ions in the diluted ferromagnetic semiconductor Zn$_{1-x}$Cr$_x$Te ($x=0.03$ 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 well correspond 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 is originated from the same electronic states of the Cr ion. Cluster-model analysis indicates that although there are two or more kinds of Cr ions in the Zn$_{1-x}$Cr$_x$Te samples, the ferromagnetic XMCD signal is originated from Cr ions substituted for the Zn site. The Cr 3d partial density of states extracted using Cr $2p \to 3d$ 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 double exchange mechanism cannot explain the ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te.