Effect of Exchange Field on the Anomalous Behaviour of 4F State of Ce in Ce1-xGdxRh3B2

Abstract

CeRh3B2 crystallizing in hexagonal (CeCo3B2 type) structure has enigmatic magnetic behaviour1. It has a lattice volume anomaly, consistent with LIII-edge x-ray absorption results 2,3 which show the presence of a small tetravalent component. Surprisingly, it undergoes ferromagnetic ordering at a temperature (Tc = 116K) higher than that of the isostructural GdRh3B2 (Tc = 90K) compound, but it has saturation moment per formula unit of only 0.4 μB. It had initially been speculated1 that magnetic order in CeRh3B2 is itinerant in nature. However, a recent neutron diffraction study4 has revealed the presence of a moment of ~ 0.6μ B at 4.2K along the c-axis at the Ce site, thereby, not precluding the possibility that a part of spin density may be located elsewhere. The above results suggest that RKKY interaction, which normally accounts for the coupling between the rare earth spins in a rare earth intermetallic compound, is either drastically modified or completely overtaken by some other mechanism CeRh3B2. In an effort to gain more insight into this mechanism and the state of the moment at Ce, we have looked into the behaviour of Ce1-xGdxRh2B2 by bulk magnetic measurements. Normally, the coupling between the rare earth spins (ferro or antiferro) is preserved5 in the mixed alloys of this kind and the magnetic ordering temperatures (Tm) vary linearly6 from one end to the other.