The magnetic refrigeration is among the most promising environment-friendly refrigeration technologies, alternative to common techniques. This new technology exploits the magnetocaloric effect, i.e. the temperature variation occurring in materials when they are subjected to a magnetic field, to produce refrigeration without requiring the compression and expansion of a gas. Materials characterized by a giant magnetocaloric effect are the best candidates for the fabrication of next-generation magnetic refrigerators. However, they are characterized by a first order phase transition which, on one hand, guarantees a larger refrigeration power but, on the other, is associated with a thermal hysteresis, which introduces a loss of refrigeration efficiency.