Muon spin rotation investigation of the S=1/2 triangular lattice LiNiO2

We have investigated S = 1/2 triangular lattice Li0.98Ni1.02O2 by a zero-field (ZF) and longitudinal-field (LF) mu SR technique. The muon signals from Li0.98Ni1.02O2 could be fitted by a stretched exponential function at low temperatures. At about 30 K the power k of the stretched exponential function becomes about k = 2 for the ZF signal, i.e. the relaxation becomes practically a Gaussian. For the LF-mu SR signals the exponent k tends to become 1 above T = 30 K, i.e. the signal becomes exponential. The relaxation rate k becomes very high at temperature below T = 10 K for the ZF data whereas k corresponding to LF data shows a maximum at T approximate to 10 K. The LF relaxation rate remains finite (0.4 mu s(-1)) at the lowest temperature (T approximate to 2 K) investigated. This indicates that even at very low temperature muon spin becomes depolarized because muons pick Up low energy excitations from the spin dynamics. We get a rough estimate of the magnetic exchange interaction of about 1 meV from the peak in the spin-spin correlation function.