Spin reorientations in RFe12$minus;xMox (R=Nd, Tb and 1.5$les;x$les;1.6) studied from polar magnetisation measurements on oriented powders

The angular dependence of the parallel and perpendicular components of the magnetisation vector with respect to the applied field, studied on oriented powders of the tetragonal compounds TbFe10.5Mo1.5 and NdFe12−xMox (x=1.5 and 1.6), allowed to more precisely know the magnetic phase diagram of these materials. In the Tb compound, the first order transition from the high temperature c-axis structure toward the low temperature planar structure at 180K comes from the vanishing of the main anisotropy constants. In the Nd compounds, we clearly showed that there is a unique second-order transition, at 120 and 90K for x=1.5 and 1.6, respectively. It takes place from the high temperature c-axis structure toward a structure in which the easy magnetisation is intermediate between the c-axis and the basal plane.