Magnetic superconductors: A review

Abstract

The recent discovery of superconductivity in some rare earth ternary and actinide compounds has led to considerable experimental and theoretical activity in the field of magnetic superconductors. The ternary compounds ErRh4B4 and HoMo6S8 exhibit reentrant superconductivity. Experimental results indicate that superconductivity and long-range ferromagnetic order coexist in a very narrow range of temperature in these two systems. Superconductivity and antiferromagnetic order truly coexist in several rare earth ternary compounds. The most important result is the anomalous behavior of the upper critical field in the vicinity of the Neel temperature. NdRh4B4 displays two antiferromagnetic transitions below the superconducting transition. The pseudoternary series Eu x Sn1−xMo6S8 containing small amounts of Br or Se exhibits the novel phenomenon of magnetic field-induced superconductivity. The compound Y9Co7 exhibits very weak itinerant ferromagnetic superconductivity. Several cerium- and uranium-based intermetallic compounds, usually known as heavy-electron metals, have been found to exhibit heavy-fermion superconductivity, characterized by a specific heat at low temperature that is two to three orders of magnitude larger than in ordinary transition metals. Several phenomenological and microscopic theories have appeared to explain the observed exciting properties of these magnetic superconductors. A brief survey of experimental and theoretical activity in this field is presented.