MAGNETISM OF METALLIC ACTINIDES

Abstract

The presence of 5f electrons in the actinide metals gives rise to magnetic behavior. In the lighter actinides, U, Np, and Pu, the magnetic properties are not simple because of strong 5f‐6d hybridization, and because the 5f electrons are fairly well extended in space. Thus, these metals do not form static, ordered moments, but have many properties which appear to be magnetic in origin. The most striking of these properties is the resistivity‐temperature behavior of pure, alpha and beta plutonium. In the heavier actinides, local moments and long‐range magnetic order seem to occur as the 5f level becomes more stable and tightly bound. Dilute alloys of actinides are found to form local‐moment Kondo systems (e.g. PdNp) and spin fluctuation systems (e.g. PdPu, ThU). Many of the intermetallic compounds having the ordered, cubic NaCl, MgCu2, and AuCu3 structures form long‐range ferro‐ and anti‐ferromagnetic structures, in addition to non‐ordered spin systems. The shift from poorly formed magnetic moments in the pure metals to long‐range order in the compounds is probably due to the reduction of 5f‐6d hybridization. It is concluded that spin fluctuation behavior is common in actinide systems, and is probably the cause of the nearly magnetic behavior of the pure, lighter metals.