Li7NMR studies on the triangular lattice systemLiCrO2

Abstract

We report $^{7}\mathrm{Li}$ NMR, magnetic susceptibility, and heat capacity measurements on the triangular lattice Heisenberg antiferromagnet compound $\mathrm{Li}\mathrm{Cr}{\mathrm{O}}_{2}$. We find that in contrast to $\mathrm{Na}\mathrm{Cr}{\mathrm{O}}_{2}$, magnetic properties of $\mathrm{Li}\mathrm{Cr}{\mathrm{O}}_{2}$ have a more pronounced three dimensional character with sharp anomalies in the temperature variation of the $^{7}\mathrm{Li}$ NMR intensity and the NMR spin-lattice relaxation rate $1∕{T}_{1}$. From heat capacity measurements we find that the total entropy related to the magnetic transition is in agreement with expectations. However, we find a significant contribution to the magnetic entropy in the range from the ordering temperature ${T}_{N}$ to nearly $4{T}_{N}$. This suggests the existence of magnetic correlations at temperatures well above ${T}_{N}$ which might be due to the frustrated nature of the system. Based on the temperature dependence of $1∕{T}_{1}$, we discuss the possible occurrence of a Kosterlitz-Thouless-Berezinskii (KTB) transition taking place at ${T}_{\mathrm{KTB}}=54\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $\mathrm{Li}\mathrm{Cr}{\mathrm{O}}_{2}$. Heat capacity data at low temperatures $(T⪡{T}_{N})$ exhibited a ${T}^{3}$ dependence and the ratio of interlayer to intralayer coupling constants, ${J}_{\ensuremath{\perp}}∕J$ in $\mathrm{Li}\mathrm{Cr}{\mathrm{O}}_{2}$ was found to be $\ensuremath{\sim}{10}^{\ensuremath{-}3}$. Lithium depletion has no significant effect on the magnetic properties and the behavior of ${\mathrm{Li}}_{0.5}\mathrm{Cr}{\mathrm{O}}_{2}$ is nearly unchanged from that of $\mathrm{Li}\mathrm{Cr}{\mathrm{O}}_{2}$.