Theoretical aspects of the magnetocaloric effect

The magnetocaloric effect is the heating or cooling of magnetic materials when subjected to magnetic field variation. It is characterized by the temperature change (ΔTad) in an adiabatic process and by the entropy change (ΔSiso) in an isothermal process. The renewed interest in the magnetocaloric effect can be attributed to Brown's work concerning the near room temperature magnetic refrigerator and Pecharsky and Gschneidner's discovery of the giant magnetocaloric effect near room temperature in Gd5Si2Ge2. After these pioneering works, the magnetocaloric effect has been intensively studied in a great number of magnetic materials. Despite this intense study, the underlying physics behind the magnetocaloric effect is not yet completely understood. In this report, we discuss the theoretical aspects of the magnetocaloric effect in rare earth metals and their alloys as well as in transition metal based compounds. In particular, we discuss the effects of pressure, doping, anisotropy and magnetoelastic interaction on the magnetocaloric potentials ΔSiso and ΔTad. The magnetocaloric effect in rare earth based compounds is discussed by using model Hamiltonians of interacting localized magnetic moments, including the crystalline electrical field interaction and the magnetoelastic coupling. The discussion of the magnetocaloric effect in transition metal based compounds is made by using model Hamiltonians based in the framework of the band theory. The results discussed in this report reveal important aspects of the magnetocaloric effect as well as point out some new perspectives on this area of research.