MONTE-CARLO SIMULATIONS OF THE MAGNETOCALORIC EFFECT IN SUPERFERROMAGNETIC CLUSTERS HAVING UNIAXIAL MAGNETIC-ANISOTROPY

The magnetic entropy change, DELTAS (hence the heating or cooling) of ferromagnetically coupled magnetic clusters induced by an application of a magnetic field is substantial and occurs over a broad temperature range. This behavior contrasts with a ferromagnetic material, where larger entropy changes can be obtained, but only over small temperature ranges close to the Curie point. Monte Carlo simulations have been carried out to obtain DELTAS when the spins are subjected to uniaxial anisotropy fields. While previous calculations for interacting spins showed increases in the Curie temperature and enhancements of DELTAS in the vicinity of the Curie point with increasing anisotropy, the present results for interacting clusters show similar increases in the temperature of DELTAS peaks accompanied by decreases in the peak values of DELTAS. These results show that the flattening of the DELTAS peaks, which make superferromagnetic materials valuable for magnetic refrigeration is assisted by the presence of uniaxial anisotropy. Some effects on DELTAS of placing the spins on fixed BCC, FCC, and sc lattices are reported.