Superconductivity and magnetism in quaternary borocarbides

Quaternary borocarbide superconductors have attracted attention and are of current interest due to a variety of reasons. Some of them exhibit high Tc's for intermetallics, including the material which shows highest known Tc for intermetallics. Though the structure of RNi2B2C (R=Sc, Y, rare earth, Th, U) is effectively a layered structure like that of high Tc cuprates, rare earth ions influence the superconducting properties of these materials. Coexistence of superconductivity and magnetism has been found in these materials with magnetic ordering temperatures much higher than those of earlier known magnetic superconductors which implies stronger coupling of rare earth moment to conduction electrons. These features make quaternary borocarbides an altogether different class of materials. Being quaternary, and with the possibility of having more than one rare earth-carbon layer in the structure, this family offers the possibility of finding many new materials with wide ranging properties. Highlights of recent developments in this new subject of quaternary borocarbides are reviewed here