MAGNETIC PROPERTIES OF FCC RARE EARTH-THORIUM ALLOYS

A neutron-diffraction study of rare earth-thorium alloys having the (fcc) structure has been carried out at temperatures ranging from room temperature to 1.3°K. For alloys of the heavy rare earth metals Tb, Ho, and Er, the fcc field starts at approximately 50 at.% Th. In a typical case the diffraction pattern at low temperatures exhibits broad diffuse maxima, due to magnetic scattering, which are centered at scattering angles and are 0.3 and 0.8 of that of the (111) nuclear reflection. The pattern can be interpreted in terms of short-range antiferromagnetic correlations. These results are to be contrasted with those previously found for the rare earth-rich hcp alloys, in which dilution by thorium stabilizes the ferromagnetic phase. For alloys of the light metals, Pr and Nd, the fcc structure is found in alloys containing 20 at.% Th. The magnetic scattering from such an alloy with Nd is similar to that observed for a polycrystalline specimen of the pure metal in which half the atomic sites have local symmetry which is cubic. It is probable that the magnetic structure of the fcc alloy is similar to the arrangement of moments on the cubic sites in the pure metal. The corresponding Pr-based alloy showed no magnetic ordering to 1.3°K. © 1968 The American Institute of Physics.