Compensation Temperature of a Mixed Ising Ferrimagnetic Model in the Presence of External Magnetic Fields

The behavior of the compensation temperature of a mixed Ising ferrimagnetic system on a square lattice in which the two interpenetrating square sublattices have spins σ (±1/2) and spins S (±1, 0) has been studied with Monte Carlo methods. Our model includes nearest and next-nearest neighbor interactions, a crystal field and an external magnetic field. This model is relevant for understanding bimetallic molecular ferrimagnetic materials. We found that there is a narrow range of parameters of the Hamiltonian for which the model has compensation temperatures and that the compensation point exists only for small values of the external field. INTRODUCTION Ferrimagnetic ordering plays a crucial role in stable crystaline room-temperature magnets, that are currently being synthesized by several experimental groups in search for materials with technological applications [1]. In a ferrimagnet the different temperature dependence of the sublattices magnetizations raises the possibility of the appearance of compensation temperatures: temperatures below the critical point, where the total magnetization is zero [2]. The temperature dependence of the coercivity at the compensation point has important applications in the field of thermomagnetic recording [3]. Mixed Ising systems are good models to study ferrimagnetic ordering [4]. Recent results show that these models can have compensation points when their Hamiltonian includes second neighbor interactions [5]. These studies have been performed in zero magnetic field. In this work we study the effect of a constant external magnetic field on the behavior of the compensation temperature, Tcomp. THE MIXED ISING MODEL Our model consists of two interpenetrating square sublattices. One sublattice has spins σ that can take two values ±1/2, the other sublattice has spins S that can take three values, ±1, 0. Each S spin has only σ spins as nearest neighbors and vice versa. The Hamiltonian of the model is given by,