OPTIMUM STRUCTURE OF MULTILAYER REGENERATOR WITH MAGNETIC-MATERIALS

We investigated a layered structural regenerator (multilayer regenerat or) with magnetic regenerator materials using a two-stage GM refrigera tor. In this study we used Er0.75Gd0.25Ni which was expected to be pla ced in the high temperature part of the second regenerator. To confirm the effect of Er0.75Gd0.25Ni, the heat-exchange efficiency of the reg enerator (regenerator efficiency) with Er0.75Gd0.25Ni, Er3Co and Er0.9 Yb0.1Ni, which were in the volumetric ratio x (0.5 - x): 0.5 (0 less t han or equal to x less than or equal to 0.5) was calculated as a funct ion of x by computer simulation. We found that the regenerator efficie ncy increased when x (i.e. the amount of Er0.75Gd0.25Ni) was increased and an optimum value of x was similar to 0.25. We then made two kinds of second regenerator: a triple layer regenerator with Er0.75Gd0.25Ni , Er3Co and Er0.9Yb0.1Ni, which were in the volumetric ratio 0.25:0.25 :0.5, and a double layer regenerator with Er3Co and Er0.9Yb0.1Ni, whic h were in the volumetric ratio 0.5:0.5. We compared their refrigeratio n performances experimentally. With the triple layer regenerator, the lowest temperature was 2.60 K at the second stage and the maximum refr igeration capacity at 4.2 K was 1.17 W. These results were superior to those with the double layer regenerator. (C) 1996 Published by Elsevi er Science Limited.