Metastability and compensation temperatures for a mixed Ising ferrimagnetic system -: art. no. 224411

In this paper we calculate the free energy of a mixed Ising ferrimagnetic system by a mean-field approach. The system consists of two interpenetrating square sublattices, one with spins +/-1,0 and the other with spins +/-1/2. We obtain the phase diagram of the system, identify the stable and metastable phases, calculate the temperature dependence of the magnetization, and give an estimate of the free-energy barrier between stable and metastable phases. By comparing our results with Monte Carlo simulations of the same model, we show that this approach gives an excellent estimate of the compensation temperatures and the magnetizations in a quite wide range of temperatures, up to quite close to the transition temperature, with a negligible computational effort. We found that when an external magnetic field is present, compensation temperatures only appear in the metastable phase, and that a system can have different compensation temperatures depending on how it is prepared. Some of these features have already been observed in experimental studies of molecular-based ferrimagnets. Our results suggest that the free-energy barrier becomes independent of the external field just at the compensation temperature.