  Generalized scaling relations and renormalization group results are used to
discuss the phase diagrams of heavy fermion systems. We consider the cases
where these materials are driven to a magnetic quantum critical point either by
applying external pressure or a magnetic field. The Ehrenfest equation relating
the pressure derivative of the critical temperature to the ratio of thermal
expansion and specific heat close to a magnetic quantum critical point (QCP) is
analyzed from the scaling point of view. We consider different phase diagrams
of antiferromagnetic heavy fermions in an external uniform magnetic field and
the implication of renormalization group results for predicting their behavior.
