Ericsson magnetic refrigeration has been studied in the temperature range from 20K to 77K. We have designed and built an Ericsson magnetic refrigerator which has a lot of difference from Carnot magnetic refrigerators. In this temperature range, it is necessary to use ferromagnetic material as the magnetic refrigerant, because it has the internal magnetic field which arranges the spin system. Moreover, above 20K since the lattice entropy grows almost comparable to or larger than the magnetic entropy, we must apply Ericsson cycle for the thermal cycle. In our apparatus, lead was used as regenerator material, and gaseous helium was used to transfer heat between the two solids, magnetic substance and regenerator material. Our device operated on Ericsson cycle with fixed magnetic substance and moving regenerator, and magnetization and demagnetization of the magnetic substance were obtained by charging and discharging the magnet. In this paper, the primary experimental results are described. The magnetic working substance was DyAl2.2 sintered compound which had the Curie temperature of 49.8K, and two kinds of regenerator were tested. At the cycle of 300s and a field of 5T, the magnetic substance changed in temperature between 48.3 and 59.1K and regenerator produced a temperature of 50.3 and 58.7K at the cold and hot end, respectively. The temperature change of the magnetic substance was about 1.7 times as large as the maximum adiabatic temperature change with the magnetic field of 0 and 5T. Some losses were discussed in our paper. The Brayton like cycle and very slow cycle period obtained in our experiment were caused by insufficient heat transfer between the regenerator and the magnetic substance. In addition to this problem, thermal conduction in the regenerator material which caused heat leak to low temperature end of the regenerator was thought to limit the temperature span produced in the regenerator.
