Here we study the effect of La-doping in EuO thin films using superconducting quantum interference device magnetometry, muon spin rotation $(\mu \mathrm{SR})$, polarized neutron reflectivity (PNR), and density functional theory (DFT). The $\mu \mathrm{SR}$ data shows that the ${\mathrm{La}}_{0.15}{\mathrm{Eu}}_{0.85}\mathrm{O}$ is homogeneously magnetically ordered up to its elevated $T_{\mathrm{C}}$. It is concluded that bound magnetic polaron behavior does not explain the increase in $T_{\mathrm{C}}$ and an Ruderman-Kittel-Kasuya-Yosida-like (RKKY-like) interaction is consistent with the $\mu \mathrm{SR}$ data. The estimation of the magnetic moment by DFT simulations concurs with the results obtained by PNR, showing a reduction of the magnetic moment per ${\mathrm{La}}_x{\mathrm{Eu}}_{1-x}\mathrm{O}$ for increasing lanthanum doping. This reduction of the magnetic moment is explained by the reduction of the number of Eu-$4f$ electrons present in all the magnetic interactions in EuO films. Finally, we show that an upwards shift of the Fermi energy with La or Gd doping gives rise to half-metallicity for doping levels as high as 3.2%.

• Received 22 May 2015

DOI:https://doi.org/10.1103/PhysRevB.92.045202