Charge Dipolar Orderings and Magnetoelastics in Rare Earth Hexaborides

Magnetoelastic effects measured previously on CexLa1-xB6 were reanalyzed based on the dynamical Jahn-Teller effect as a single site effect and the paired distortion as an interaction effect developed in recent papers for RB6 in general. In the dilute systems, we observe an anomalous Curie-Weiss term caused from competition between the single site effect and the pair effect, while in the dense systems anomalies due to pair formation are observed even in the paramagnetic region. Strong frustration inherent to the pair ordering plays an important role. Anomalous properties in PrB6 and NdB6 were also interpreted based on the above common model in good agreement with the experimental results, in particular with anomalous neutron scattering measurement. Magnetoelastic effects were measured also on PrB6 and NdB6. In PrB6 the effect is 100 time stronger than that in CeB6 due to induced mixing through distortions between the nearly degenerated ground levels, Gamma(1) and Gamma(5). The charge dipolar ordering was also observed clearly at the lower ordering temperature T-2, forcing an incommensurate magnetic ordering to commensurate.