Multilayer Ceramic Regenerator Materials for 4 K Cooling

The ceramics oxide magnetic materials have shown excellent properties for use as regenerator materials used in 4 K crycoolers. Currently four kinds of oxide magnetic materials GdVO4, GAP=GdAlO3, GOS=Gd2O2S and Tb2O2S are available for applications for regenerators or thermal anchors from 2 K to 8 K. This paper focused on controlling the heat capacity of the (GdxTb1−x)2O2S system to cover the refrigeration temperatures between 6 K and 8 K. A concept of multilayer regenerator material consisting of multicomponent magnetic materials has been proposed and investigated. Two‐layer ceramic material including two kinds of magnetic materials (Gd0.1Tb0.9)2O2S+Tb2O2S was successfully fabricated in the form of regenerator particles with an average diameter of 0.25 mm. Measured heat capacity data showed that it had twin peaks relating to those of (Gd0.1Tb0.9)2O2S and Tb2O2S, and the entire curve became broader and wider. The mechanical properties of strength and hardness of the two‐layer ceramic material were the same as other ceramic regenerator materials like GOS. Thus, it is concluded that the multilayer ceramic material is very useful to control the heat capacity of the regenerator particles. The cooling tests using the two‐layer ceramic material with HoCu2 and GOS have been done to investigate the 2nd stage regenerator configuration.