Rare-earth metal transition metal borocarbide and nitridoborate superconductors

Abstract

Few years after the discovery of superconductivity in high-T c cuprates, borocarbides and shortly after nitridoborates with reasonably high T c s up to about 23 K attracted considerable attention. Particularly for the rare-earth metal series with composition RNi 2 [B 2 C] it turned out, that several members exhibit superconductivity next to magnetic order with both T c above or below the magnetic ordering temperature. Therefore, these compounds have been regarded as ideal materials to study the interplay and coexistence of superconductivity and long range magnetic order, due to their comparably high ordering temperatures and similar magnetic and superconducting condensation energies. This review gathers information on the series RNi 2 [B 2 C] and isostructural compounds with different transition metals substituting Ni as well as related series like RM[BC], RM[BN], AM[BN] and R 3 M 2 [BN] 2 N (all with R = rare-earth metal, A = alkaline-earth metal, M = transition metal) with special focus on synthesis, crystal structures and structural trends in correspondence to physical properties.