X-RAY AND SUSCEPTIBILITY STUDY OF FIRST-ORDER MAGNETIC TRANSFORMATION IN MN3PT

The first-order transformation from triangular to collinear antiferromagnetic structure (AF-AF transformation) has been investigated in the Mn3Pt1-xRhx and Mn3+yPt 1-y systems by x-ray diffraction and magnetic methods. At the AF-AF transformation temperature Tt a discontinuous change in the lattice parameter is observed with a magnitude depending on concentration but with always the same lattice parameter value of the collinear phase. This implies the existence of a critical lattice parameter value for the AF-AF transformation. Below the Néel temperature TN an anomaly in the thermal expansion occurs indicating exchange interactions dependent on the interatomic separation. This anomaly differs in sign for the collinear-paramagnetic and triangular-paramagnetic transitions. The susceptibility shows an abrupt change at Tt and a maximum at TN in the triangular phase. No maximum occurs for the collinear phase. The observed transition temperatures are in agreement with the earlier neutron diffraction data. © 1968 The American Institute of Physics.