^{7}Li NMR Study of Heavy Fermion LiV2O4 Containing Magnetic Defects

TL;DR

This study investigates how magnetic defects affect the ^7Li NMR properties of LiV2O4, revealing inhomogeneous magnetic behavior and differences between powders and single crystals at very low temperatures.

Contribution

It provides a detailed analysis of magnetic defect effects on NMR and magnetization in LiV2O4, highlighting differences between powders and single crystals and proposing a model for defect distribution.

Findings

Magnetic defects cause inhomogeneous NMR spectra and relaxation rates.

Powder samples show spin freezing below 1.0 K, single crystals do not.

Different defect behaviors likely due to synthesis conditions.

Abstract

We present a systematic study of the variations of the ^{7}Li NMR properties versus magnetic defect concentration up to 0.83 mol% within the spinel structure of polycrystalline powder samples and a collection of small single crystals of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report static magnetization measurements and ac magnetic susceptibility measurements at 14 MHz on the samples at low temperatures. Both the NMR spectrum and nuclear spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic defects. The NMR data for the powders are well explained by assuming that (i) there is a random distribution of magnetic point defects, (ii) the same heavy Fermi liquid is present in the samples containing the magnetic defects as in magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and of the Fermi liquid on the magnetization and NMR properties are separable. In the single crystals, somewhat different behaviors are observed. Remarkably, the magnetic defects in the powder samples show evidence of spin freezing below T ~ 1.0 K, whereas in the single crystals with similar magnetic defect concentration no spin freezing was found down to 0.5 K. Thus different types of magnetic defects and/or interactions between them appear to arise in the powders versus the crystals, possibly due to the substantially different synthesis conditions of the powders and crystals.