Influence of the substrate temperature on the Curie temperature and charge carrier density of epitaxial Gd-doped EuO films

Rare earth doping is a standard, yet experimentally poorly understood method to increase the Curie temperature $(TC)$ of the ferromagnetic semiconductor EuO. Here, we report on the charge carrier density $(n)$ and the $TC$ of commonly used 4.2 at. % Gd-doped EuO films grown by molecular-beam epitaxy on (110) oriented $YAlO3$ substrates at various substrate temperatures $(Tsub)$⁠. Increasing $Tsub$ leads to a decrease in $n$ and $TC$⁠. For high substrate temperatures the Gd-doping is rendered completely inactive: $n$ and $TC$ drop to the values of undoped EuO.