抄録
Many rare-earth compounds have been studied to attain a large volumetric specific heat in cryogenic temperatures and to aim at developing regenerator materials for a regenerative refrigerator. The magnetic specific heats of these materials are so large that the performance of refrigeration for a Gifford-McMahon refrigerator has been greatly improved and helium temperatures have been attained. In an application for the superconducting magnet, the refrigerator must be operated under the magnetic field. So, magnetic regenerator materials are required to be free from the influences of the magnetic field. In this paper, the magnetic field influences on the regenerator materials Er3Ni, ErNi and Er3Co, are discussed and Ho2Al is proposed as a new regenerator material which is free from the influence of the magnetic field. The magnetic properties of Er3Ni, ErNi and Er3Co were investigated at cryogenic temperatures in a magnetic field of up to 5 Tesla. The magnetic forces were evaluated for these materials under the magnetic field using the magnetic moment values deduced from the magnetization measurements. The magnetic forces for ferromagnetic materials such as the ErNi and Er3Co turned out to be one order of magnitude larger than that for antiferromagnetic material Er3Ni. It was confirmed that the antiferromagnetic material is superior to the ferromagnetic one in case of the exposure to the large magnetic field and large gradient of the field. Further, new antiferromagnetic regenerator materials were searched and Ho2Al was found to have a volumetric specific heat as large as Er3Co in the temperature range from 10 to 16K.
