Optimum structure of multilayer regenerator with magnetic materials

Abstract We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerator materials using a two-stage GM refrigerator. In this study we used Er 0.75 Gd 0.25 Ni which was expected to be placed in the high temperature part of the second regenerator. To confirm the effect of Er 0.75 Gd 0.25 Ni, the heat-exchange efficiency of the regenerator (regenerator efficiency) with Er 0.75 Gd 0.25 Ni, Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio x: (0.5 − x): 0.5 (0 ≤ x ≤ 0.5) was calculated as a function of x by computer simulation. We found that the regenerator efficiency increased when x (i.e. the amount of Er 0.75 Gd 0.25 Ni) was increased and an optimum value of x was ~ 0.25. We then made two kinds of second regenerator: a triple layer regenerator with Er 0.75 Gd 0.25 Ni, Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio 0.25:0.25:0.5, and a double layer regenerator with Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio 0.5:0.5. We compared their refrigeration performances experimentally. With the triple layer regenerator, the lowest temperature was 2.60 K at the second stage and the maximum refrigeration capacity at 4.2 K was 1.17 W. These results were superior to those with the double layer regenerator.