Self-consistent renormalization theory of spin fluctuations in paramagnetic spinel LiV2O4

TL;DR

This paper develops a self-consistent renormalization theory to describe spin fluctuations in LiV$_2$O$_4$, successfully explaining low-temperature neutron scattering data and trends at higher temperatures.

Contribution

It introduces a phenomenological SCR theory tailored to LiV$_2$O$_4$, incorporating a unique ${f q}$-space distribution of spin fluctuations and fitting experimental data.

Findings

Accurately reproduces temperature dependence of static susceptibility and relaxation rate below 30K.

Predicts main trends of spin fluctuation behavior at temperatures above 30K.

Describes evolution of neutron scattering intensity from low to higher ${f q}$ with temperature.

Abstract

A phenomenological description for the dynamical spin susceptibility $\chi({\bf q},\omega;T)$ observed in inelastic neutron scattering measurements on powder samples of LiV$_2$O$_4$ is developed in terms of the parametrized self-consistent renormalization (SCR) theory of spin fluctuations. Compatible with previous studies at $T\to 0$, a peculiar distribution in ${\bf q}$-space of strongly enhanced and slow spin fluctuations at $q \sim Q_c \simeq$ 0.6 $\AA^{-1}$ in LiV$_2$O$_4$ is involved to derive the mode-mode coupling term entering the basic equation of the SCR theory. The equation is solved self-consistently with the parameter values found from a fit of theoretical results to experimental data. For low temperatures, $T \lesssim 30$K, where the SCR theory is more reliable, the observed temperature variations of the static spin susceptibility $\chi(Q_c;T)$ and the relaxation rate $\Gamma_Q(T)$ at $q\sim Q_c$ are well reproduced by those suggested by the theory. For $T\gtrsim 30$K, the present SCR is capable in predicting only main trends in $T$-dependences of $\chi(Q_c;T)$ and $\Gamma_Q(T)$. The discussion is focused on a marked evolution (from $q \sim Q_c$ at $T\to 0$ towards low $q$ values at higher temperatures) of the dominant low-$\omega$ integrated neutron scattering intensity $I(q; T)$.