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.
Bruce Normand, Ying Chen, Sheng Xu, Shuo Li, Xiaoyu Xu, Zeyu Wang, Weiqiang Yu