NMR Evidence of Antiferromagnetic Spin Fluctuations in Nd<sub>0.85</sub>Sr<sub>0.15</sub>NiO<sub>2</sub>
Yi Cui, Cong Li, Qing Li, Xiyu Zhu, Ze Hu, Yi-feng Yang, Jinshan Zhang, Rong Yu, Hai-Hu Wen, Weiqiang Yu
Abstract
Despite the recent discovery of superconductivity in Nd 1– x Sr x NiO 2 thin films, the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle. Here we report the 1 H NMR measurements on powdered Nd 0.85 Sr 0.15 NiO 2 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> is strongly enhanced when lowering the temperature, developing a broad peak at about 40 K, then decreases following a spin-wave-like behavior <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>∝</mml:mo> <mml:msup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> 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 Nd 0.85 Sr 0.15 NiO 2 , and shed light on the mechanism of superconductivity observed in films of nickelates.