Temperature-dependent spin-resolved electronic structure of EuO thin films

TL;DR

This study combines experimental spin-resolved photoemission spectroscopy and theoretical calculations to analyze the temperature-dependent electronic structure of EuO thin films, revealing exchange interactions, hybridization, and the effects of magnetic phase transition.

Contribution

It provides new insights into the exchange splitting mechanisms and the role of O 2p levels in EuO, supported by combined experimental and theoretical approaches.

Findings

Exchange splitting in O 2p levels vanishes at Curie temperature

Hybridization between Eu 4f and O 2p states observed

Significant spin-orbit effects predicted in Eu 4f bands

Abstract

The electronic structure of the ferromagnetic semiconductor EuO is investigated by means of spin- and angle-resolved photoemission spectroscopy (spin-ARPES) and density functional theory. EuO exhibits unique properties of hosting both weakly-dispersive nearly fully polarized Eu $4f$ bands, as well as O $2p$ levels indirectly exchange-split by the interaction with Eu nearest neighbors. Our temperature-dependent spin-ARPES data directly demonstrates the exchange splitting in O $2p$ and its vanishing at the Curie temperature. Our calculations with a Hubbard $U$ term reveal a complex nature of the local exchange splitting on the oxygen site and in conduction bands. We discuss the mechanisms of the indirect exchange in the O 2p levels by analyzing orbital-resolved band characters in ferromagnetic and antiferromagnetic phases. The directional effects due to spin-orbit coupling are predicted theoretically to be significant in particular in the Eu 4f band manifold. The analysis of the shape of spin-resolved spectra in the Eu $4f$ spectral region reveals signatures of hybridization with O $2p$, in agreement with the theoretical predictions. We also analyze spectral changes in the spin-integrated spectra throughout the Curie temperature and demonstrate they derive from both the magnetic phase transition and effects due to sample aging, unavoidable for this highly reactive material.