Pressure induced magnetic transition of Mn3Ga1-xAlxC

We have measured the magnetization of Mn3Ga1-xAlxC with x = 0, 0.01 and 0.02 under pressure up to 1.25 GPa. A magnetic transition from an antiferromagnetic (AFM) to an intermediate (IM) state with spontaneous magnetization is observed under pressure. We have determined the phase diagram in the pressure-temperature plane. The application of pressure increases the magnetization in the ferromagnetic (FM) phase for all these compounds. We have also measured the thermal expansion of Mn3Ga0.97Al0.03C. It is consistent with the pressure effects on the magnetization and suggests the magnetic contribution to the thermal expansion as omega(m)(FM) < omega(m)(IM) < omega(m)(AFM). Neutron diffraction experiments were performed on Mn3Ga0.95Al0.05C. Bragg peaks corresponding to an antiferromagnetic component were observed in the IM state. It is highly possible that the IM state has a canted ferromagnetic structure.