Field-induced valence transition in rare-earth system

The magnetic field-induced valence transition in rare-earth compound has been examined based on a pseudospin S=1 Ising model proposed earlier for valence transition. The model includes finite mixing between two pertinent ionic configurations (magnetic and non-magnetic) separated by an energy gap and with intersite interaction between rare-earth ions. Using the mean field approximation the magnetic behaviour and the critical field (Hc) for transition are obtained as a function of energy gap and temperature. The phase boundary defined in terms of reduced field Hc/Hco and reduced temperature T/Tv (Tv being valence transition temperature in absence of field) is nearly independent of energy gap. These results are in qualitative agreement with experimental observation in Yb- and Eu-compounds