Abstract
The criteria of selecting magnetic materials for a refrigerant of the magnetic refrigerator in the temperature range from 4.2K to 300K have been considered.
First, by assuming the molecular field approximation, we have calculated the magnetic entropy SM(T, H) of the typical 3-dimensional ferromagnetic substance near the Curie temperature as a function of temperature and magnetic field strength. In order to examine the usefulness of the above theoretical results, the magnetocaloric effects of Cr3Te4 and Gd near the room temperature have been investigated experimentally. As a result of comparison of the calculated results with the experimental ones, it is confirmed that both of those results are in good agreement with each other.
Second, by using the Debye approximation, the temperature variation of the lattice entropy SL(T) as a function of the Debye temperature has been made clear. Using the above SM(T, H) and SL(T), the temperature and magnetic field dependences of the calculated total entropy of the several typical ferromagnets are obtained.
In view of the above results we have discussed the several criteria for the magnetic refrigerant used near the room temperature to be satisfied.
