Conventional magnetic materials heat up when they
Conventional magnetic materials heat up when they are placed in a magnetic field and cool down when they are removed. This phenomenon is known as the MCE. In recent years, the researchers have directed their attention to the study of materials with giant MCE including manganites. The MCE is the basis for magnetic refrigeration, may be parameterized as adiabatic changes of temperature, isothermal changes of AS-252424 or isothermal heat. Usually, an isothermal application of a magnetic field μ0H decreases the configurational entropy of the spin structure. Consequently, an adiabatic demagnetization allows the spins to randomize again and causes cooling. Magnetic refrigerators are a new environmentally friendly option to the conventional devices based on compression expansion of gases.
From the physical point of view, magnetocaloric materials can be classified according to the magnetic phase transition they undergo. For the materials exhibiting the conventional MCE, where the magnetic transitions are of the second order type, the contribution to the entropy (ΔS) is only of magnetic origin. On the other hand, materials with first order magnetic phase transition (FOMT) show giant MCE, where ΔS also includes a considerable contribution from the lattice through the latent heat. However, FOMT have two important drawbacks, namely, the narrowness of the magnetic entropy change (ΔSM) curve and the presence of a large thermal and/or field hysteresis, which leads to low operation frequencies and cooling power .