119Sn solid-state NMR as a local probe for correlations in CeRu4Sn6

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Abstract

CeRu4Sn6 is a tetragonal ternary compound which develops strong correlations at low temperatures. NMR investigations on the Sn(I=12)119 nuclei are reported for the first time. The Knight shift K(T)119 at magnetic fields of about 1.8 T is relatively small (-0.33%) and no significant temperature dependence could be resolved. The behavior of the spin–lattice relaxation rate (1/T1)119 at temperatures above approximately 20 K is consistent with a small gap semiconductor (1/T1Texp(-Δ/kBT),Δ/kB=33K). At lower temperatures (1/T1)119 shows an increase towards weaker T-dependence. This is interpreted as the formation of strong correlations around T*=10K and is consistent with specific heat results in the framework of the Korringa model. Furthermore, measurements on the isostructural reference compound LaRu4Sn6 are presented.

Introduction

Triggered by investigations of electrical resistivity and specific heat identifying CeRu4Sn6 as a dense Kondo system, we performed solid-state NMR investigations on CeRu4Sn6 (hereafter referred to as Ce146) and the non-magnetic compound LaRu4Sn6 (La146) [1], [2], [3]. The absence of magnetic ordering indicates the dominance of the Kondo effect and suggests heavy fermion behavior [2]. In this paper, temperature-dependent NMR investigations on the 119Sn nuclei (Knight shift K(T)119, spin–lattice relaxation rate (1/T1)119) of polycrystalline powder samples of Ce146 and La146 are presented.

Section snippets

Experimental

The investigated Ce146 sample was prepared by fixing randomly orientated microcrystals in paraffin. The material used here is from the same batch as that from Ref. [3]. Further details of sample preparation were reported elsewhere [3]. Sn(I=12119, γn/2π=15.867MHz/T) NMR measurements were performed using a standard pulsed field sweep NMR spectrometer at a fixed frequency of ν=28.5 MHz. The 119Sn NMR spectra for several temperatures were obtained by tracing the spin–echo intensity as a function

Results and discussion

Measurements of the magnetic susceptibility χ of Ce146 (not shown here) reveal local moment behavior at higher temperatures. Above T80K, the susceptibility data are consistent with a Curie–Weiss behavior with an effective moment μeff=2.88μB nearly equal to the free Ce3+ ion value. There is only a weak reduction of the moment at low temperatures. The results of the 119Sn field sweep NMR spectra of Ce146 and La146 observed at T=2K, 10 K and 100 K (ν=28.5MHz) are shown in Fig. 1. The linewidth for

Conclusions

119Sn field sweep spectra of CeRu4Sn6 show small and nearly constant K(T). The temperature dependence of the spin–lattice relaxation rate 1/T1 exhibits semiconducting behavior down to T20K with a gap value of Δ/kBT=33K. The low-temperature 1/T1-upturn is interpreted as the formation of strong correlations around T*=10K, which is consistent with specific heat measurements. We conclude that in CeRu4Sn6, a correlated ground state forms out of a low-carrier density of states.

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