A Model for Correlated Metamagnets: Application to UPt${}_3$ and CeRu${}_2$Si${}_2$

In a model system with three S=1 pseudo-spins situated in an anisotropic mean field we compute the thermodynamic response in a self consistent manner. An adhoc uniform broadening of all energy levels of the (localized) spins due to their interaction with conduction electrons is introduced. The results with a minimal set of parameters reproduce with remarkable fidelity the properties of the strongly correlated metamagnets UPt${}_3$ and CeRu${}_2$Si${}_2$. Several key predictions are made for further experimental confirmation.