Spin Fluctuations in the Ground State of Doped Quantum Spin System TlCu_1−xMg_xCl₃ with x=0.0047 Probed by Muon-Spin-Relaxation Technique

Abstract

Zero- and longitudinal-field muon-spin-relaxation (ZF- and LF-μSR) measurements were carried out down to T=20 mK on the slightly doped quantum spin system TlCu_1−xMg_xCl₃ with x=0.0047, in which a magnetic phase transition is observed at 0.70 K by specific heat measurement. LF-μSR measurements above and below the phase transition temperature revealed that the impurity-induced magnetic moments of the Cu-3d spins slowly fluctuate at a frequency of 0.74 MHz at T=20 mK, far below the magnetic phase transition temperature. It is possible that the impurity-induced magnetic moments are in an exotic state where they fluctuate while preserving their wave vector and relative phase, i.e., a coherently fluctuating state.