# Valence state of Sm in single crystalline EuO thin films

## TL;DR

This study investigates the valence state of samarium in EuO thin films, revealing that despite expectations, Sm predominantly remains trivalent due to local lattice adjustments.

## Contribution

It demonstrates that Sm in EuO thin films stays mainly trivalent, contrary to expectations based on lattice size, highlighting local lattice flexibility effects.

## Key findings

- Sm in EuO thin films is mainly trivalent.
- Lattice flexibility allows local adjustment to stabilize Sm$^{3+}$.
- Surprising stabilization of Sm$^{3+}$ despite larger lattice constant.

## Abstract

Samarium has two stable valence states, 2+ and 3+, which coexist in many compounds forming spatially homogeneous intermediate valence states. We study the valence state of samarium when incorporated in a single crystalline EuO thin film which crystallizes in a $fcc$-structure similar to that of the intermediate valence SmO, but with a larger lattice constant. Due to the increased lattice spacing, a stabilization of the larger Sm$^{2+}$ ion is expected. Surprisingly, the samarium incorporated in Sm$_{\mathrm{x}}$Eu$_{\mathrm{1-x}}$O thin films shows a predominantly trivalent character, as determined by x-ray photoelectron spectroscopy and magnetometry measurements. We infer that the O$^{2-}$ ions in the EuO lattice have enough room to move locally, so as to reduce the Sm-O distance and stabilize the Sm$^{3+}$ valence.