Magnetocaloric effect in metamagnetic systems

We propose a model to account for the magnetocaloric effect associated with field-driven first-order magnetic transitions. The model is based on an Ising model for the magnetic degrees of freedom which are coupled to lattice vibrations. The coupling is introduced within the framework of a bond proportion model, which assumes that nearest-neighbor pairs of antiparallel and parallel spins have different stiffness. The model is solved by means of a variational mean field technique and it is found that, for strong enough coupling, it displays a field-induced first-order magnetic transition. The magnetocaloric properties are obtained and results are compared with experimental results reported for systems undergoing metamagnetic transitions.