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

Abstract: We revisit the magnetic properties of the antiferromagnetic Kondo lattice CeNiAsO by $<sup>{75}$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 $T_{N2}&lt;T&lt;T_{N1}$ and $T&lt;T_{N2}$ 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 $T<sup>*\sim15$ 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 $<sup>{75}$As nuclear magnetic resonance studies under pressure.