Half-Heusler compounds UPtSn and ThPtSn: [formula omitted] and [formula omitted] NMR studies

Abstract

Intrinsic magnetic susceptibilities of ThPtSn and UPtSn have been determined from the analysis of magnetisation isotherms recorded in the temperature range 1.9–300 K, and in magnetic field strengths up to 5 T. ThPtSn is found to be diamagnetic. Susceptibility data of UPtSn exhibit a cusp-like behaviour in the vicinity of 35 K and Curie–Weiss law above 150 K. Microscopic properties of UPtSn have been studied by Sn119 and Pt195 NMR Knight shift, K, and the spin–lattice relaxation rate 1/T1 in the paramagnetic state (35K<T<300 K). The Knight shift K(T) versus susceptibility χ(T) plots at temperatures T≥150 K yield the transferred hyperfine fields of +51.6 kOe/μB for Sn119 nuclei, and − 13.5 kOe/μB for Pt195 nuclei. Plots of K(T) against χ(T) for T<150 K exhibit a deviation from the linear behaviour indicative of crystalline field effects. The temperature dependence of the 1/T1 data of Pt195 nuclei is consistent with a model of electronic structure possessing an energy gap Δ=12.3 meV and can explain the reported activated resistivity. Paramagnetic impurities act as relaxation centers in ThPtSn. Rapid spin diffusion plays an important role in Pt195 relaxation while Sn119 nuclear spins relax directly through dipole–dipole interactions with electron spins on magnetic impurities.