Preparation of Gd-doped EuO1-x thin films and the magnetic and magneto-transport properties

Polycrystalline europium monoxide (EuO) films doped with and without Gd were prepared using a reactive deposition method in a MBE system. Two different electron doping methods, Gd substitution and oxygen deficiency, enhance the Curie, temperature (T-C) and the temperature dependence of magnetization differently. Gd doping increases T-C up to 125 K, while oxygen deficient samples enhance it above 150 K. The enhanced TC is attributed to the increase in the indirect exchange interaction between Eu2+ spins via conduction electrons. The resistivities as a function of temperature for both quasi-stoichiometric (QS) EuO and QS-GdxEu1-xO show maxima near 70 and 110 K, respectively. The conduction band magnetic splitting explains the resistivity behaviours. Both the temperature dependences of the large magneto-resistance and the absorption edge are also interpreted by the conduction band magnetic splitting mechanism. The unusual blue shift observed in Gd-doped,samples is not yet-understood.