Equiatomic transition metal alloys of manganese IV. A neutron diffraction study of magnetic ordering in the PtMn phase

From x-ray and neutron diffraction and magnetic susceptibility measurements, the PtMn phase with the CuAuI type structure is found to exhibit anti-ferromagnetic arrangement of the magnetic moments with spin quantum number 4/2 for the Mn atoms and 0 for the Pt atoms. The moments of nearest-neighbour Mn atoms in (001) planes are anti-parallel to each other, and the direction of the moments changes from parallel to c in alloys with 50 at. % Pt and less, to perpendicular to c with more than 50 at. % Pt. Néel temperatures are observed in the range from 840° to 970°K. At lower temperatures the alloys show weak ferromagnetism which is believed to result from canting of the moments.