NMR Evidence of Antiferromagnetic Spin Fluctuations in Nd$_{0.85}$Sr$_{0.15}$NiO$_2$

TL;DR

This study uses NMR to reveal antiferromagnetic spin fluctuations and short-range magnetic order in bulk Nd$_{0.85}$Sr$_{0.15}$NiO$_2$, providing insights into electron correlations relevant to superconductivity in nickelate films.

Contribution

It provides the first NMR evidence of antiferromagnetic fluctuations and magnetic ordering in bulk Nd$_{0.85}$Sr$_{0.15}$NiO$_2$, linking magnetic properties to superconductivity mechanisms.

Findings

Detection of increasing NMR linewidth with decreasing temperature.

Observation of a peak in spin-lattice relaxation rate at 40 K.

Evidence of antiferromagnetic fluctuations and short-range order.

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 remain 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 and exhibits an upturn behavior at low temperatures. The spin-lattice relaxation rate $1/^{1}T_1$ is strongly enhanced when lowering the temperature, developing a broad peak at about 40 K, then decreases following a spin-wave-like behavior $1/^{1}T_1{\sim}T^2$ 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 Nd$_{0.85}$Sr$_{0.15}$NiO$_2$, and shed light on the mechanism of superconductivity observed in films of nickelates.