Pressure Induced Magnetic Transition of Mn3Ga1-xAlxC

We have measured the magnetization of Mn 3 Ga 1- x Al x C 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 Mn 3 Ga 0.97 Al 0.03 C. It is consistent with the pressure effects on the magnetization and suggests the magnetic contribution to the thermal expansion as ω m FM < ω m IM < ω m AFM . Neutron diffraction experiments were performed on Mn 3 Ga 0.95 Al 0.05 C. 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.