NMR Evidence of Antiferromagnetic Spin Fluctuations in Nd0.85Sr0.15NiO2

Despite the recent discovery of superconductivity in Nd1-x Sr (x) NiO2 thin films, the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle. Here we report the H-1 NMR measurements on powdered Nd0.85Sr0.15NiO2 samples by taking advantage of the enriched proton concentration after hydrogen annealing. We find a large full width at half maximum of the spectrum, which keeps increasing with decreasing the temperature T and exhibits an upturn behavior at low temperatures. The spin-lattice relaxation rate T-1(1)-1 is strongly enhanced when lowering the temperature, developing a broad peak at about 40 K, then decreases following a spin-wave-like behavior T-1(1)-1 proportional to T-2 at lower temperatures. These results evidence a short-range glassy antiferromagnetic ordering of magnetic moments below 40 K and dominant antiferromagnetic fluctuations extending to much higher temperatures. Our findings reveal the strong electron correlations in bulk Nd0.85Sr0.15NiO2, and shed light on the mechanism of superconductivity observed in films of nickelates.