X-ray diffraction study of the structural phase transition in MnAs under high magnetic fields

The structural phase transition induced by magnetic fields on MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature T-C was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above T-C. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at T-C with increasing temperature from 290 to 319 K via two-phase coexistence region. The X-ray diffraction profiles at 319 K showed the single phase of the MnP-type structure in zero field and applying magnetic field of 3 T caused appearance of the Brag peak of the hexagonal structure. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above T-C were first order with a hysteresis and had a close relationship between each other. (C) 2004 Elsevier B.V. All rights reserved.