The Effect of Lu Doping on Ferromagnetic EuO

Europium Oxide (EuO) is a poorly understood ferromagnetic semiconductor whose spin-ordering temperature (T$_{C})$ can be greatly influenced by the inclusion of dopants such as oxygen vacancies or one of several trivalent ions. The ability to grow high-quality crystalline and stoichiometric EuO by adsorption-controlled growth using molecular-beam epitaxy is imperative in separating the effect of oxygen vacancies from that of trivalent dopants. In this study, we have prepared 5{\%} Lu-doped EuO and characterized the effects of this doping on the magnetic and electronic properties. We show for the first time that Lu is a viable dopant material for EuO, increasing the T$_{C}$ up to 120K as a result of an increase in the carrier concentration to 1.8x10$^{26 }$m$^{-3}$ from 1.0x10$^{23 }$m$^{-3}$. This is on par with other EuO films grown in an adsorption-controlled environment and doped with La or Gd. Furthermore, we find that EuO maintains a high spin-polarization ($>$80{\%}) at this doping level. As a result of the simultaneously high T$_{C}$ and high spin-polarization, EuO can be considered for spintronic applications at much higher temperatures than possible for undoped EuO.