NO-assisted molecular-beam epitaxial growth of nitrogen substituted EuO

TL;DR

This study demonstrates a controlled method for nitrogen substitution in EuO thin films using molecular beam epitaxy with NO gas, revealing the effects on oxidation states and magnetic properties, and providing a model for magnetic state interactions.

Contribution

It introduces a novel NO-assisted growth technique for EuO films with tunable nitrogen content and explores the resulting electronic and magnetic properties.

Findings

Nitrogen is incorporated as N3- in EuO films.

Eu3+ formation correlates with nitrogen substitution.

Ferromagnetism persists despite Eu3+ presence, with unchanged Curie temperature.

Abstract

We have investigated a method for substituting oxygen with nitrogen in EuO thin films, which is based on molecular beam epitaxy distillation with NO gas as the oxidizer. By varying the NO gas pressure, we produce crystalline, epitaxial EuO_(1-x)N_x films with good control over the films' nitrogen concentration. In-situ x-ray photoemission spectroscopy reveals that nitrogen substitution is connected to the formation Eu3+ 4f6 and a corresponding decrease in the number of Eu2+ 4f7, indicating that nitrogen is being incorporated in its 3- oxidation state. While small amounts of Eu3+ in over-oxidized Eu_(1-delta)O thin films lead to a drastic suppression of the ferromagnetism, the formation of Eu3+ in EuO_(1-x)N_x still allows the ferromagnetic phase to exist with an unaffected Tc, thus providing an ideal model system to study the interplay between the magnetic f7 (J=7/2) and the non-magnetic f6 (J=0) states close to the Fermi level.