Spin fluctuations probed by NMR in paramagnetic spinel LiV$_2$O$_4$: a self-consistent renormalization theory

TL;DR

This paper develops a self-consistent renormalization theory to describe low-temperature spin fluctuations in LiV$_2$O$_4$, successfully matching experimental NMR relaxation data and revealing the approach to magnetic instability under pressure.

Contribution

A novel SCR theory for AFM spin fluctuations in LiV$_2$O$_4$ is introduced, explaining temperature and pressure effects on NMR relaxation rates.

Findings

SCR theory accurately reproduces experimental $1/T_1$ data

Spin fluctuations develop as the system nears magnetic instability under pressure

Low-temperature upturn in $1/T_1T$ attributed to spin freezing of defects

Abstract

Low frequency spin fluctuation dynamics in paramagnetic spinel LiV$_2$O$_4$, a rare 3$d$-electron heavy fermion system, is investigated. A parametrized self-consistent renormalization (SCR) theory of the dominant AFM spin fluctuations is developed and applied to describe temperature and pressure dependences of the low-$T$ nuclear spin-lattice relaxation rate $1/T_1$ in this material. The experimental data for $1/T_1$ available down to $\sim 1$K are well reproduced by the SCR theory, showing the development of AFM spin fluctuations as the paramagnetic metal approaches a magnetic instability under the applied pressure. The low-$T$ upturn of $1/T_1T$ detected below 0.6 K under the highest applied pressure of 4.74 GPa is explained as the nuclear spin relaxation effect due to the spin freezing of magnetic defects unavoidably present in the measured sample of LiV$_2$O$_4$.