Structural and magnetic properties of Mn 1− tNi tAs

Abstract

The phase diagram of Mn 1- t Ni t As shows a variety of transitions between states with different magnetic and crystal structure properties. These structures and the corresponding phase transitions are investigated by powder X-ray and neutron diffraction, DSC and magnetic susceptibility measurements as functions of composition ( t), temperature, external pressure and applied magnetic field. At high temperatures complete solid solution of an NiAs type, paramagnetic state exists over the entire composition range. At and below room temperature the crystal structures of the solid solution phases are of the regular NiAs, MnP and NiAs types for the composition intervals 0.00⩽ t⩽0.025±0.005, 0.025±0.005⩽ t⩽0.22±0.02 and 0.65± 0.04⩽ t⩽1.00, respectively. For 0.22±0.02< t<0.65±0.04 below about 650 K incommensurate superstructures, resulting from ordering of the Mn and Ni atoms, are imposed on the basic NiAs and MnP type structures. Helimagnetic ordering of the H a type is found for the MnP type solid solution phase at temperatures below ≈200 K. In the superstructural range, antiferromagnetism prevails for 0.30⩽ t⩽0.50 at low temperatures. The full hysteresis region between NiAs, ferro, MnP, para and MnP, heli ( H a ) type states for compositions close to MnAs is studied in magnetic fields up to 250 kOe and for external pressures up to 10 kbar.