Magnetic Properties of Some Rare-Earth Alloys at High Pressures

The Néel and Curie temperatures of some alloys of the heavy rare-earth metals with each other and with yttrium have been measured as functions of pressure up to ∼85 kbar. The initial slopes ($\frac{\mathrm{dT}}{\mathrm{dP}}$) are approximately proportional to the average de Gennes function ($\Sigma i^{}{c}_i{(g_i-1)}^2{J}_i(J_i+1)$). In the molecular field approximation with a first-order correction for the anisotropy energy, the change in the exchange interaction with lattice parameter is given by $\frac{k^{-1\mathrm{}}dJ\left(\mathrm{Q}\right)}{\mathrm{da}}=(42\mathrm{}\pm 6)°$K/Å. It is suggested that this is caused mainly by a change in the generalized conduction-electron susceptibility with pressure. A polymorphic transition from a hexagonal-close-packed structure to a Sm-type structure is found with increasing pressure in many of these alloys, and the Sm-type phase has two ordering temperatures. The higher ordering temperature of the Sm-type phase is 10% lower than that of the hcp phase, and the two ordering temperatures in the Sm-type phase differ by 17%.