Basics of the magnetocaloric effect

This chapter reviews the basic aspects governing magnetocaloric materials from the physics and thermodynamics viewpoint. The thermodynamics of magnetic materials is discussed by introducing the relevant free energy terms together with their microscopic origin and the sources of the magnetic field induced entropy change. Particular attention is devoted to magnetic transitions of the first order type which involves the coupling of different degrees-of-freedom such as: spin, lattice, electronic, magneto-crystalline anisotropy and others. The problem of the irreversibility and hysteresis, present in magnetocaloric materials with transitions of the first order, is discussed in the context of out-of- equilibrium thermodynamics and hysteresis modeling.