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

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 $EuO1-xNx$ 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 $Eu1-δO$ thin films lead to a drastic suppression of the ferromagnetism, the formation of $Eu3+$ in $EuO1-xNx$ 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.