AUTHOR=Miyazaki Hidetoshi , Hajiri Tetsuya , Matsunami Masaharu , Inukai Manabu , Ito Takahiro , Kimura Shin-ichi 

TITLE=Observation of Thickness-Dependent Exchange Interaction in EuO Ultrathin Films

JOURNAL=Frontiers in Nanotechnology

VOLUME=4

YEAR=2022

URL=https://www.frontiersin.org/journals/nanotechnology/articles/10.3389/fnano.2022.872717

DOI=10.3389/fnano.2022.872717

ISSN=2673-3013

ABSTRACT=<p>The electronic structure of single-crystalline EuO (100) ultrathin films, together with their exchange splitting energy (<italic>ΔE</italic><sub>EX</sub>) and ferromagnetic phase transition temperature (<italic>T</italic><sub>C</sub>), was investigated by temperature- and thickness-dependent angle-resolved photoemission spectroscopy. Both <italic>ΔE</italic><sub>EX</sub> and <italic>T</italic><sub>C</sub> decreased monotonically with decreasing film thickness. The band shift showed an opposite thickness dependence at the Γ and X points, reflecting the balance of the hybridization between the Eu 4<italic>f</italic> and O 2<italic>p</italic> states (super-exchange interaction) and between the Eu 4<italic>f</italic>, O 2<italic>p</italic>, and Eu 5<italic>d</italic> states (indirect-exchange interaction). The observed transition from an indirect energy gap in the bulk to a direct gap in the ultrathin films of the ferromagnetic semiconductor EuO could be potential in future spintronic devices.</p>