Magnetism in praseodymium-neodymium single-crystal alloys

Pr-Nd alloys represent an almost ideal model system for a mixture of singlet-doublet ions (S eff =1) and Kramers' doublet ions (S eff = 1 / 2 ). Neutron scattering and magnetization measurements have been made on single crystals of Pr-3.0% Nd, Pr-5.5% Nd and Pr-26.3% Nd. These alloys order antiferromagnetically (on the hexagonal sites) at 6.3K, 6.5K and 11.4K, respectively. Measurements of the magnetic-field dependence of the magnetization were also made. The concentration dependence of T N and the temperature dependence and magnitude of the induced moments can be understood in terms of a simple molecular-field theory. The authors conclude that pure Pr has a close-to-critical ratio between exchange interaction and the crystal field (=0.95). The crystal field acting on the Nd ion is smaller than that acting on Pr. The exchange interactions between Pr-Pr, Nd-Nd, and Pr-Nd are found. The relative magnitudes agree with the de Gennes scaling factor.