Magnetic Phase Transition of MnP Under Magnetic Field

Neutron diffraction studies on the magnetic phase transition have been carried out by using single crystal of MnP. Successive phase transitions from screw, fan and ferromagnetic long range order were confirmed by applying magnetic field along the crystalline b axis. The magnetization measurements which give a saturation value of 1.33±.01 µ B per Mn atom afford experimental derivation of the absolute cross section for all the magnetic reflections. This provides us the exact value of the magnetic moment in every phase at 4.2 K. The controversy is eliminated completely; there is no change of the magnetic moment through the screw-fan transition, and the circular helix is concluded. The quantitative agreement of the present results is achieved with Kitano-Nagamiya theory in the fan state. The field dependence of the wave vector Q a of the fan state implies an additional evidence of the band character inherent in MnP.