Recent progress in the application of magnetic regenerator materials

Various magnetic materials have a large peak in heat capacity C(T) in the vicinity of liquid helium temperature at Te (magnetic phase transition temperature). However, a single magnetic material is not sufficient for regenerative operations since the peak in C(T) is narrow. Therefore, an important consideration in the development of a magnetic regenerator is the sequencing of the magnetic materials so as to produce the best C(T) distribution. To find out the highest heat exchange effectiveness of a regenerator (regenerator effectiveness), a study was conducted into the effectiveness of multi-layer regenerators composed of several rare-earth compounds with different Tc by computer simulation. The simulation clearly indicated that regenerator effectiveness increases as the number of layers is increased. Among all the different compounds tested, maximum effectiveness was obtained in the case of a Due-layer regenerator of Er0.9Yb0.1Ni and Er3Co; a three-layer regenerator of ErNi0.8Co0.2, Er0.9Yb0.1Ni and Er-3 Co; and a four-layer regenerator of ErNi0.8Co0.2, Er0.9Yb0.1Ni, ErNi and Er-3 Co inserted in sequence from cold to hot. The refrigeration power of a four-layer regenerator is expected to be twice as much as that of a single-layer Er-3 Ni.