Incommensurate to commensurate antiferromagnetism inCeRhAl4Si2: AnAl27NMR study

Abstract

$^{27}\mathrm{Al}$ nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of ${\text{CeRhAl}}_{4}{\text{Si}}_{2}$, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of ${T}_{\mathrm{N}1}=14$ K and ${T}_{\mathrm{N}2}=9$ K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below ${T}_{\mathrm{N}2}$, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between ${T}_{\mathrm{N}1}$ and ${T}_{\mathrm{N}2}$. The spin-lattice relaxation rate suggests that the $4f$ electrons behave as local moments at temperatures above ${T}_{\mathrm{N}1}$.