Evidence for continuous change of spin states between impurity-induced order and pressure-induced order in TlCu0.985 Mg0.015 Cl3 probed via muon spin rotation

Zero- and longitudinal-field muon spin relaxation (ZF- and LF-μSR) measurements were carried out in pressures up to 2 kbar in impurity-doped TlCu0.985 Mg0.015 Cl3 of which the magnetic phase-transition temperature under ambient pressure in zero field is 2.85 K. The spontaneous muon spin precession, which indicates the existence of a long-range coherent order, is observed above 0.5 kbar at 2.3 K. In ambient pressure, the existence of the static internal magnetic field is confirmed by LF-μSR measurements, however, no rotational signal is observed down to 0.29 K. These results indicate that the crossover reported by IImamura [Phys. Rev. B 74, 064423 (2006)] is the continuous change from a short-range order to a long-range coherent order.