Magnetic Behaviour of CeRh_3−xIr_xB₂ Alloy System

Abstract

The anomalous magnetic properties of CeRh₃B₂, crystallising in the hexagonal CeCo₃B₂ type structure, have received considerable attention in recent years. Despite a lattice volume anomaly and an unusually short Ce-Ce distance of 3.09 Å, much smaller than the nearest neighbour distance of 3.41 Å in the non magnetic α-Ce, CeRh₃B₂ orders magnetically with an unusually high Curie temperature (T_C) of 115K and with a saturation moment of 0.4 μ_B only [1]. Surprisingly, GdRh₃B₂ orders at a lower temoerature [2] with T_C = 90K, in apparent contradiction to what one would expect on the basis of de Gennes scaling. On the other hand, isostructural CeRu₃B₂, which exhibits a larger lattice volume anomaly, undergoes a transition to superconducting state at about 1K [3]. The application of external pressure [4] has rather insignificant effect on the ordering temperature of CeRh₃B₂ $\left(\frac{dlnTc}{dP} = 0.09\% / \text{kbar}\right)$ implying negligible valence instability in conformity with conclusions from the L_III-edge measurements [5,6] which reveal an f-count of nearly one.