The inverse magnetocaloric effect occurs when a magnetic material cools down under applied magnetic field in an adiabatic process. Although the existence of the inverse magnetocaloric effect was recently reported experimentally, a theoretical microscopic description is almost nonexistent. In this paper we theoretically describe the inverse magnetocaloric effect in antiferro- and ferrimagnetic systems. The inverse magnetocaloric effects were systematically investigated as a function of the model parameters. The influence of the Néel and the compensation temperature on the magnetocaloric effect is also analyzed using a microscopic model.

We report a way of obtaining the magnetocaloric effect due to the crystal electrical-field quenching of the total angular momentum in a magnetic system where a strong spin reorientation is present. The theoretical model is applied to DyAl 2 and the results predict a considerable magnetic entropy change by rotating a single crystal in a fixed magnetic field. The obtained temperature and magnetic-field dependencies of the magnetization component along the ͗111͘-crystallographic direction are in good agreement with the recently reported experimental data.

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We report on calculations of the anisotropic magnetocaloric effect in DyAl 2 using a model Hamiltonian including crystalline electrical field effects. The anisotropic effect is produced by the rotation of a constant magnetic field from the easy to a hard magnetic direction in the crystal and is enhanced by the first order nature of the field induced spin reorientation transition. The calculated results indicate that for a field with modulus of 2 T rotating from a hard to the easy direction, the isothermal magnetic entropy ͑⌬S iso ͒ and adiabatic temperature ͑⌬T ad ͒ changes present peak values higher than 60% the ones observed in the usual process, in which the field direction is kept constant and the modulus of the field is varied.

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