The effect of randomness on the quantum spin system Tl$_{1-x}$K$_x$CuCl$_3$ with ${\boldmath $x$}$ = 0.44 studied by the Zero-field Muon-Spin-Relaxation (ZF-$μ$SR) method

Abstract

Zero-field muon-spin-relaxation (ZF-{\boldmath $μ$}SR) measurements were carried out down to 80 mK on the randomness bond system Tl$_{1-x}$K$_x$CuCl$_3$ with $x$ = 0.44. Time spectra are well fitted by the stretched exponential function $\exp (-λt)^β$. The muon spin relaxation rate $λ$ increases rapidly with decreasing temperature, and $β$ tends to 0.5 at 80 mK. The divergent increase of $λ$ suggests the critical slowing down of the frequency of the Cu-3{\it d} spin fluctuations toward a spin frozen state below 80 mK, and the root-exponential-like behavior of the time spectrum indicates that the origin of the relaxation is possibly the spatially-fixed fluctuating dilute moments.

Accepted on J. Phys. Soc. Jpn