$^{75}$As NMR study of the antiferromagnetic Kondo lattice compound CeNiAsO

TL;DR

This study uses $^{75}$As NMR to investigate magnetic transitions and spin dynamics in CeNiAsO, revealing successive antiferromagnetic phases, a Knight shift anomaly indicating $c-f$ coherence, and quasi-two-dimensional spin fluctuations.

Contribution

It provides detailed NMR insights into the magnetic order, coherence onset, and spin fluctuation dimensionality in CeNiAsO, advancing understanding of Kondo lattice behavior.

Findings

Two antiferromagnetic transitions at 9.0 K and 7.0 K.

Observation of Knight shift anomaly below 15 K.

Evidence of quasi-two-dimensional spin fluctuations.

Abstract

We revisit the magnetic properties of the antiferromagnetic Kondo lattice CeNiAsO by $^{75}$As nuclear magnetic resonance measurements. Our results confirm two successive antiferromagnetic transitions of Ce moments at $T_{N1}=9.0(3)$ K and $T_{N2}=7.0(3)$ K. Incommensurate and commensurate antiferromagnetic orders are suggested for $T_{N2}<T<T_{N1}$ and $T<T_{N2}$ respectively, consistent with previous neutron and muon experiments. A Knight shift anomaly, characterized by the failure of $K(T)-\chi(T)$ scaling, is observed below $T^*\sim15$ K, which gives a measure of the onset of coherent $c-f$ correlations. This energy scale is further confirmed by the spin-lattice relaxation rate ($1/T_1$). The analysis of spin dynamics also reveals a quasi-two-dimensional character of spin fluctuations in CeNiAsO. This work paves the way for further $^{75}$As nuclear magnetic resonance studies under pressure.