Pressure-induced new magnetic phase in Tl(Cu_0.985Mg _0.015)Cl₃ probed by muon spin rotation

We carried out zero-field muon-spin-rotation (ZF-μSR) measurements in hydrostatic pressures in impurity-doped quantum spin gap system Tl(Cu _0.985Mg_0.015)Cl₃ to investigate microscopic magnetic properties of the pressure-induced phase. The spontaneous muon spin precession, which indicates the existence of a long-range coherent order, is observed in pressures. With decreasing temperature in 3.1 kbar, the internal static magnetic field at the muon sites H_int tends to saturate to 280 Oe around 4 K, however, decreases to 240 Oe at 2.3 K. These results suggest a rearrangement of ordered spins, and we speculate that the oblique antiferromagnetic phase, which is observed in the pressure of 14 kbar on the pure TlCuCl₃, appears in the Mg-doped system in lower pressures.