Magnetic and neutron diffraction studies on (Co_1-xMn_x)₂P

Magnetic and neutron diffraction studies on the series of mixed (Co_1-xMn_x)₂P phosphides are described. The magnetisation of CoMnP has been measured as a function of field at 4.2 K. The temperature dependence of the magnetisation along the b axis of the compounds with x=0.2, 0.5, 0.63 and 0.65 has been measured. Single-crystal neutron diffraction data at room temperature were used to refine the structure of two compositions with x=0.5 and 0.62. Polarised neutron measurements on CoMnP are interpreted in terms of antiferromagnetic-like domains associated with the orientation of the cobalt moments. The spin wave dispersion relations of CoMnP and (Co_1-xMn_x)₂P, x=0.65, have been determined at 300 K and in a low-temperature helical phase for the latter. A theoretical understanding of these results is possible in terms of the canting of cobalt moments due to a Dzyaloshinski-Moriya interaction.