Magnetic Properties of Some Alloys of Thorium with Holmium and Erbium

Abstract

Neutron diffraction studies have been carried out on a number of alloys of thorium with the heavy rare-earth metals Ho and Er, as part of an investigation of the nature of the exchange interaction in these materials. At room temperature, the heavy rare earths in question crystallize in the simple hcp structure; thorium, in the ccp structure. Alloys containing more than about 80 at. % rare earth are found in the hcp structure, and those with less than about 50 at. % are found in the ccp arrangement. The three outer electrons of the rare-earth metals (5d16s2) are presumed to form conduction bands, and it is generally accepted that magnetic coupling in the rare-earth metals occurs via an indirect interaction involving a polarization of the conduction electrons. Thorium, a tetravalent diluent (outer electron configuration 6d27s2), provides a means of changing the effective number of conduction electrons on alloying of the rare earths. In contrast to the effect of trivalent yttrium and lutetium as diluents, small additions of thorium tend to stabilize the ferromagnetic state in the hcp structure. Attempts at correlation of the results with the Ruderman-Kittel-Kasuya-Yosida theory have been made but with indifferent success.