Ferromagnetism and Superconductivity

Abstract

Since the discovery of superconductivity, ferromagnetism and super­ conductivity have been considered exclusive phenomena. It was assumed that the large internal magnetic field in a ferromagnetic material would not allow it to become a superconductor. And actually, thus far none of the magnetic elements, such as chromium, manganese, iron, cobalt, and nickel, have exhibited superconductivity. In 1957 Ginzburg (1) theorized that ferromagnetism and superconductivity are two mutually exclusive pheno­ mena. Later, the possibility of a similarity between superconducting and magnetic interactions was proposed. Matthias, Suhl & Corenzwit (2) were the first to suggest the simultaneous occurrence of superconductivity and ferromagnetism in certain substituted cubic-Laves phase intermetallic compounds. Previously, the interaction between superconductivity and ferromagnet­ ism was explored by introducing small amounts of magnetic impurities into superconducting elements and compounds. These materials often consisted of clusters of magnetic impurities, which made it difficult to interpret the physical data. In recent years, a series of new ternary compounds with the structure MRh4B4 (where M = Th, Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, or Lu), and rare-earth molybdenum chalcogenides were discovered. In these compounds, the rare-earth ions are distributed periodically in the lattice and their magnetic moments have long-range order, as opposed to the diffuse "spin glass" ordering of dilute substitutional alloys.