Magnetic and structural phase transitions in ferromagnetic MnBi

X-ray powder diffraction, magnetization measurements, and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in zero magnetic field as will as in magnetic fields of up to 14 T and in the temperatures range of 300-773 K, in order to investigate magnetic phase transition. In zero magnetic field, a magnetic phase transition from ferromagnetic to paramagnetic state is exhibited at temperature (T _t) of 628 K, accompanied by decomposition. With increasing magnetic field up to 14 T, T _t increases linearly with the rate of 2 KT ^-1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T _t. The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in the interval of 626-623 K, which relates to the metamagnetic transition. The obtained results are discussed on the basis of a mean field theory.