Self-consistent renormalization theory of spin fluctuations in paramagnetic spinelLiV2O4

Abstract

A phenomenological description for the dynamical spin susceptibility $\ensuremath{\chi}(\mathbf{q},\ensuremath{\omega};T)$ observed in inelastic neutron scattering measurements on powder samples of $\mathrm{Li}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ is developed in terms of the parametrized self-consistent renormalization (SCR) theory of spin fluctuations. Compatible with previous studies at $T\ensuremath{\rightarrow}0$, a peculiar distribution in $\mathbf{q}$ space of strongly enhanced and slow spin fluctuations at $q\ensuremath{\sim}{Q}_{c}\ensuremath{\simeq}0.6\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{\ensuremath{-}1}$ in $\mathrm{Li}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ 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, $T\ensuremath{\lesssim}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where the SCR theory is more reliable, the observed temperature variations of the static spin susceptibility $\ensuremath{\chi}({Q}_{c};T)$ and the relaxation rate ${\ensuremath{\Gamma}}_{Q}(T)$ at $q\ensuremath{\sim}{Q}_{c}$ are well reproduced by those suggested by the theory. For $T\ensuremath{\gtrsim}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the present SCR is capable of predicting only main trends in $T$ dependences of $\ensuremath{\chi}({Q}_{c};T)$ and ${\ensuremath{\Gamma}}_{Q}(T)$. The discussion is focused on a marked evolution (from $q\ensuremath{\sim}{Q}_{c}$ at $T\ensuremath{\rightarrow}0$ toward low $q$ values at higher temperatures) of the dominant low-$\ensuremath{\omega}$ integrated neutron scattering intensity $I(q;T)$.