Performance of ceramic magnetic regenerator materials for sub-2 K cryocoolers

A new ceramic magnetic regenerator material GdVO4 has been fabricated and tested. The new regenerator material has an antiferromagnetic transition at 2.2 K with a large heat capacity more than 0.8 J/cm(3)K. The cooling tests with a 0.1 W-class GM cryocooler have been done with He-3 gas as a working fluid. The 2nd regenerator consisted of Pb, HoCu2, Gd2O2S, GdAlO3 and GdVO4. The configuration was adjusted by partially replacing the GdAlO3 with the GdVO4. A cooling capacity at 1.8 K for the 2nd regenerator was increased by about 10% and the minimum cooling temperature was obtainable at 1.4 K. The cooling test results show that the high heat capacity magnetic materials are useful to provide both the higher cooling capacity and the lower minimum temperature, but more precise adjustments are needed to optimize the configuration of the regenerator.