Orbital character of O 2p unoccupied states near the Fermi level in CrO2

TL;DR

This study investigates the orbital character and magnetic properties of unoccupied O 2$p$ states near the Fermi level in CrO$_2$ using advanced spectroscopic techniques, revealing details about its electronic structure and magnetic behavior.

Contribution

The paper provides detailed experimental evidence on the orbital character and polarization of O 2$p$ states in CrO$_2$, supporting a half-metallic ferromagnet model with significant exchange splitting.

Findings

O 2$p_y$ orbitals hybridize with Cr 3$d_{xz-yz}$ states.

A narrow band (~0.7 eV) is observed above $E_F$ only excited by electric field perpendicular to the c-axis.

CrO$_2$ exhibits a large exchange splitting (~3.0 eV) and correlation effects.

Abstract

The orbital character, orientation, and magnetic polarization of the O 2$p$ unoccupied states near the Fermi level ($E_F$) in CrO$_2$ was determined using polarization-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) from high-quality, single-crystal films. A sharp peak observed just above $E_F$ is excited only by the electric field vector ($\bf E$) normal to the tetragonal $c$-axis, characteristic of a narrow band ($\approx$ 0.7 eV bandwidth) constituted from O 2$p$ orbitals perpendicular to $c$ (O 2$p_y$) hybridized with Cr 3$d_{xz-yz}$ $t_{2g}$ states. By comparison with band-structure and configuration-interaction (CI) cluster calculations our results support a model of CrO$_2$ as a half-metallic ferromagnet with large exchange-splitting energy ($\Delta_{exch-split}$ $\approx$ 3.0 eV) and substantial correlation effects.