7Li NMR studies on the triangular lattice system LiCrO2

We report Li-7 NMR, magnetic susceptibility, and heat capacity measurements on the triangular lattice Heisenberg antiferromagnet compound LiCrO2. We find that in contrast to NaCrO2, magnetic properties of LiCrO2 have a more pronounced three dimensional character with sharp anomalies in the temperature variation of the Li-7 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 4T(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-KTB=54 K in LiCrO2. Heat capacity data at low temperatures (T < T-N) exhibited a T-3 dependence and the ratio of interlayer to intralayer coupling constants, J(perpendicular to)/J in LiCrO2 was found to be similar to 10(-3). Lithium depletion has no significant effect on the magnetic properties and the behavior of Li0.5CrO2 is nearly unchanged from that of LiCrO2.