A pseudospin S = 1 Ising model, which simulates the general behaviour of valence transition in rare-earth compounds, is proposed. The model includes tunnelling (mixing) between two pertinent configurations involved in the transition. The phase boundary between abrupt and smooth transitions and other physical properties are obtained by mean-field approximation. The magnetic susceptibility is Curie-like at high temperatures and saturates at low temperatures. This saturation behaviour of susceptibility and the absence of magnetic ordering at low temperatures is found to be the consequence of the tunnelling effect.

Sobhendu K. Ghatak

Papers

Pseudospin model for valency transition