Magnetic ordering under hydrostatic pressure in doped spin gap systems ACu1-xMgxCl3:A=TlACu1-xMgxCl3:A=Tl and K

Magnetic phase transitions under hydrostatic pressures in spin gap systems TlCu0.988Mg0.012Cl3TlCu0.988Mg0.012Cl3 and KCu0.973Mg0.027Cl30.973Mg0.027Cl3 were investigated by magnetization measurements. The present doped systems exhibit impurity-induced magnetic orderings. With increasing pressure, ordering temperature TNTN increases. With a further increase in pressure, the present systems undergo phase transitions to uniform antiferromagnetic phases due to the closing of the triplet gap in the intact dimers. The crossover from the impurity-induced ordered phase to the uniform antiferromagnetic phase occurs at P≃1.3kbar for TlCu0.988Mg0.012Cl3TlCu0.988Mg0.012Cl3.