New Magnetic Superconductors: A Toy Box for Solid-State Physicists

Over the past decade, discussion of the interaction between superconductivity and magnetism has been overshadowed by the omnipresence of the oxide‐based, high‐temperature superconductors. But interest in the interaction between these two generally competing effects has a history that predates high‐$T_c$ materials by several decades. Starting with seminal work by Bernd Matthias and his coworkers, it was found that magnetic impurities strongly suppress superconductivity in pure elements and binary compounds. This rapid suppression of the superconducting transition temperature $T_c$ was due to the local magnetic moment of the impurity preventing the formation of the spin‐up/spin‐down conduction‐electron pairs that are responsible for superconductivity. The early measurements were made on dilute alloys, and for many solid‐state physicists of the time, the quest was to find compounds in which superconductivity coexists with an ordered lattice of local magnetic moments.