Pressure Induced Magnetic Transition of Mn₃Ga_1-xAl_xC

抄録

We have measured the magnetization of Mn₃Ga_1-xAl_xC 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 Mn₃Ga_0.97Al_0.03C. 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 Mn₃Ga_0.95Al_0.05C. 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.