Magnetic polarization in the Ramirez-Falicov model of valency-change transitions; application to cerium

We have extended the Ramirez‐Falicov model of the α‐γ phase transition of cerium, allowing for a field‐induced or spontaneous splitting of the bands and of the six‐fold degenerate 4f level. To this end, we had to introduce two new parameters in the theory to take account of conduction electron‐f electron and conduction electron‐conduction electron exchange. The value of the latter can be estimated from the low‐temperture susceptibility of α cerium, for the former an upper limit can be found on the basis of the phase diagram. We find the effect of presently available magnetic fields on the α‐γ transition temperature in cerium to be negligible according to this theory. With higher values (not appropriate to cerium) for the conduction electron‐f electron exchange parameter, the model shows first and second order transitions to a ferromagnetic γ phase. The relative stability of this phase with respect to the α phase is higher than that of the paramagnetic γ phase; under certain circumstances there is no direct paramagnetic γ→α transition.