Magnetic phase diagram ofNd0.5Sr0.5MnO3probed byO17NMR

We have used $^{17}\mathrm{O}$ NMR to probe the magnetic homogeneity in both the paramagnetic and the ferromagnetic states of a high-quality ${\mathrm{Nd}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ single crystal. The measured broadening of the $^{17}\mathrm{O}$ line reveals that significant two-dimensional static correlations of neighboring Mn spins in the $ab$ planes exist in the paramagnetic phase far above the transition. Our results also indicate that the ferromagnetic metallic state at low temperatures, resulting from the melting of the charge ordered (charge-exchange type) insulating state in $94\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, is rather inhomogeneous: regions with almost perfect long-ranged ferromagnetic order coexist with regions with poor ferromagnetic (FM) order. The latter regions represent about 25% of the sample and are due to inherent structural strains inside the FM domain.