Magnetic refrigeration is a promising alternative technology for cooling and gas liquefaction. This technology takes advantage on the magnetocaloric effect. This intrinsic property of some magnetic materials is the consequence of magneto-thermal coupling between the lattice entropy and the magnetic entropy. When a magnetic field is applied to the magnetic material (ferromagnet), the magnetic moments of its atoms become aligned making the material more ordered. Consequently, in adiabatic conditions the decrease of the magnetic entropy is compensated by an increase of the lattice entropy and accordingly of the temperature. Conversely, when the magnetic field is removed, the magnetic moments return to their random directions, magnetic entropy increase and the material is forced to cool down. Thus, with materials presenting a giant magnetocaloric effect we can manufacture efficient and ecological cooling systems with a theoretical efficiency from 20 to 30% better than the traditional refrigeration. Currently, pure gadolinium (Gd) is the only material used in the magnetic refrigeration prototypes. The use of gadolinium as active refrigerant brings several disadvantages, first Gd is too much expensive (≈ 4000$/kg), secondly the refrigeration is limited to temperatures near room temperature where the magnetocaloric effect is very important because of its Curie temperature (TC = 294 K). Finally, gadolinium oxidizes easily, which on long terms results in degradation of the performance of the refrigerator. Aiming to replace gadolinium metal in magnetic refrigeration systems, my work consists to investigate new materials or to develop and optimize the existing magnetocaloric compounds for magnetic refrigeration as rare earth, R-Co2 (R: rare earth), La(Fe1-xSix)13, pnictides ...etc based compounds.
