Anisotropic p-f mixing mechanism explaining anomalous magnetic properties in Ce monopnictides

An anomalously small crystal-field splitting in the paramagnetic region in CeSb and CeBi compared with those in CeP and CeAs is explained by the mixing mechanism between the occupied 4f states and the valence band holes. In the paramagnetic regions, the above p-f mixing gives the effective crystal-field splitting, which is estimated to nearly cancel the normal splittings extrapolated from CeP and CeAs in good agreement with experiment. The formula for the second-order transition temperature, at which the population ratio of the 4f GAMMA8 states begins to be unbalanced, is also derived. In CeBi the second-order transition may occur, while in CeSb the first-order transition should occur in agreement with experiments. (author)