Monte Carlo study of a mixed spin-3/2 and spin-1/2 Ising ferrimagnetic model

The magnetic properties of a mixed Ising ferrimagnetic model on a square lattice, in which the two interpenetrating square sublattices have spins that can take two values, σ=±1/2, alternated with spins that can take four values, S=±3/2,±1/2, are studied. This model can be relevant for understanding the magnetic behavior of the new class of organometallic ferrimagnetic materials that exhibit spontaneous magnetic moments at room temperature. We carried out exact ground-state calculations for the model and employ a Monte Carlo algorithm to obtain the finite-temperature phase diagram for both the transition and compensation temperatures. The role of the different interactions in the Hamiltonian is explored. When only the nearest-neighbor interaction and the crystal-field term are included our results indicate no compensation point at finite temperature. When the next-nearest-neighbor interaction between the spins σ=±1/2 exceeds a minimum value that depends on the other parameters in the Hamiltonian, a compensation point appears. The interaction between the S=±3/2 spins, next-nearest neighbors in the lattice, has the effect of changing the compensation temperature.