ABSTRACT
In this chapter we discuss the application of magnetic materials in refrigeration devices. The magnetic materials can be used in this field by two ways. As known, magnetic materials make additional contributions to the heat capacity related to the magnetic subsystem, which is especially large near the magnetic phase transition points. That is why the magnetic materials with the low ordering temperatures can provide high heat capacity in the low-temperature region where lattice and electronic heat capacities approach zero. This circumstance allows the use of such materials in passive magnetic regenerators-the devices serving to expand a conventional refrigerator temperature span. The described application of magnetic materials can be called ‘passive’ because here they only adsorb and desorb heat at different stages of the refrigerator cycle, do not produce heat themselves and operate without application of a magnetic field. In this way magnetic materials are used now in cryocoolers, essentially increasing their effectiveness. But more interesting and perspective application is related to the magnetocaloric effect inherent in magnetic materials. We mean the use of magnetic materials in magnetic refrigeration devices as working bodies, as a ‘heart’ of these devices. Such an application can be called ‘active’ (here a magnetic material produces heat under magnetization) and will be considered in detail in this chapter. It is worth noting, however, that in some cases both ‘passive’ and ‘active’ properties of a magnetic material are used simultaneously-for example, in so-called magnetically augmented regenerators, which are also discussed below.
