Observation of Thickness-Dependent Exchange Interaction in EuO Ultrathin Films

• Published in: Frontiers in nanotechnology Vol. 4
• Main Authors: Miyazaki, Hidetoshi, Hajiri, Tetsuya, Matsunami, Masaharu, Inukai, Manabu, Ito, Takahiro, Kimura, Shin-ichi
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 30-06-2022
• Subjects: electronic structure; EuO; photoemission spectroscopy; spintronic device; ultrathin films
• ISSN: 2673-3013; 2673-3013
• DOI: 10.3389/fnano.2022.872717

The electronic structure of single-crystalline EuO (100) ultrathin films, together with their exchange splitting energy (
ΔE
EX
) and ferromagnetic phase transition temperature (
T
C
), was investigated by temperature- and thickness-dependent angle-resolved photoemission spectroscopy. Both
ΔE
EX
and
T
C
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
f
and O 2
p
states (super-exchange interaction) and between the Eu 4
f
, O 2
p
, and Eu 5
d
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.