Refrigeration capacity of a GM refrigerator utilizing HoSb as its regenerative material

In order to obtain better regenerative effectiveness at very low temperatures, the heat capacity of the regenerator materials must be larger than that of He as the working gas. The specific heat of pressurized He gas has a large peak below 15 K. Only magnetic materials, whose phase-transition temperatures exist in the low temperature region, can be effective as regenerative materials and only multi-layer regenerators with magnetic materials have practical use. Two magnetic compounds were found to have remarkably large peak values. One such compound is HoSb with the peak value of 2.7 J/K.cm 3 at 5 K, and the other is DySb with 2.0 J/K.cm 3 at 9 K. Materials with a very large peak in heat capacity were packed into a regenerator and the structure of the materials was analyzed by computer simulation. The combination of multi-layer structure with synthetic materials are considered best in the structure of a regenerator. HoSb and HoCu2, which has a broad peak below 10 K, were packed into the second stage of a GM refrigerator as the multi-layer materials and the refrigeration capacities of the materials were compared. It seems that HoSb is effective for use in the refrigerator below 6 K.