Magnetic Properties of Rare-Earth Metals and Alloys

Abstract

A review of neutron diffraction studies of the magnetic properties of rare‐earth metals and alloys is presented. For each of the pure metals Tb, Dy, Ho, Er, and Tm there is observed a transition at a temperature T_N to an oscillatory antiferromagnetic configuration (helical or linear oscillator type). At lower temperatures, further transitions to ferromagnetic, ferromagnetic spiral, or antiphase domain‐type configurations are observed. For Gd, only the ferromagnetic configuration is found. The magnetic moments in the ordered configurations at low temperatures approach the values expected from the corresponding free tripositive ions. In the first half of the series only Nd has been studied by single‐crystal methods, but Ce, Pr, and Eu have now been investigated with polycrystalline samples. The data for Ce are complicated by the existence of several allotropic forms, but a complex antiferromagnetic structure appears to be associated with the hexagonal form at low temperatures. For Nd and Pr, oscillatory antiferromagnetic configurations are observed at very low temperatures in which, as in Ce, the moments have magnitudes considerably smaller than the free‐ion values, which result suggests a strong influence due to the crystalline field. A helical spin structure in bcc Eu has been reported in which the moment of Eu is somewhat smaller than that of Eu⁺⁺. A number of alloy systems, R‐Y, R‐R′, and R‐La, where R and R′ are among the group Tb–Tm, have been investigated and results are discussed. These results and those for the pure metals are discussed relative to the theory of the magnetism of the rare‐earth metals.