Recent progress in the magnetic materials for regenerator in the range from 4.2 K to 20 K

In order to improve the performance of small refrigerators below 20 K, a new material with high specific heat is necessary for a regenerator material, because the specific heats of current regenerator materials, such as lead, decrease extremely below 20 K. In the present investigations it has been made clear that magnetic materials, which have high specific heats near their phase transition temperatures, are the most promising materials. Moreover, the application of magnetic material for regenerator has the advantage of optimization of regenerator structure. For example the authors can select suitable materials in the layer structure regenerator. Consequently, those magnetic phase transition temperatures must be arbitrarily controllable. Accordingly, the authors have investigated some rare earth compounds and their solid solutions, such as RNi2, where R is heavy rare earth element. Several typical experimental results are shown