Magnetic properties of pure and Gd-doped EuO probed by NMR

An Eu NMR study in the ferromagnetic phase of pure and Gd-doped EuO was performed. A complete description of the NMR line shape of pure EuO allowed for the influence of doping EuO with Gd impurities to be highlighted. The presence of a temperature-dependent static magnetic inhomogeneity in Gd-doped EuO was demonstrated by studying the temperature dependence of the line shapes. The results suggest that the inhomogeneity in 0.6% Gd-doped EuO is linked to colossal magnetoresistance. The measurement of the spin-lattice relaxation times as a function of temperature led to the determination of the value of the exchange integral J as a function of Gd doping. It was found that J is temperature independent and spatially homogeneous for all samples and that its value increases abruptly with increasing Gd doping.