Abstract
Magnetic materials play a significant role in improvement of regenerative cryocooler performance, because they have high volumetric specific heat at magnetic transition temperatures. Gadolinium oxysulfide (Gd2O2S, GOS) that has an antiferromagnetic transition at 5 K improved the cooling performance of cryocoolers when it was used in colder side of the second stage regenerator operating below 10 K. Small magnetic susceptibility and specific heat insensitive to magnetic field is important in order to reduce influence of magnetic field on the performance of cryocooler. We measured magnetization and specific heat of ceramic GOS in magnetic field up to 5 T. The magnetization of GOS represented typical temperature dependence for antiferromagnetic materials and no metamagnetic transition was observed. As for specific heat of GOS, peak temperature decreased from 5.5 to 5.0 K with increasing magnetic field from 0 to 5 T and the transitions remained sharp in magnetic fields. Thermal conductivity of GOS was observed to have very small magnetic field dependence.
Highlights
Cryocoolers with lowest temperature of 4 K realized superconducting magnet systems and 3He-4He dilution refrigerators without liquid helium
In order to improve regenerative cryocooler performance, magnetic materials play a significant role in regenerator efficiency because they have high volumetric specific heat at magnetic transition temperature
The transitions remained sharp in magnetic fields
Summary
Cryocoolers with lowest temperature of 4 K realized superconducting magnet systems and 3He-4He dilution refrigerators without liquid helium. In order to improve regenerative cryocooler performance, magnetic materials play a significant role in regenerator efficiency because they have high volumetric specific heat at magnetic transition temperature. Various magnetic materials such as Er3Ni, HoCu2 and GdAlO3 were studied. We measured magnetization and specific heat of ceramic GOS in magnetic field from 0 to 5 T. As for specific heat of GOS, the peak temperature decreased from 5.5 to 5.0 K with increasing magnetic field from 0 to 5 T and the transitions remained sharp in magnetic fields. It was observed that the field dependence was very small From these results, ceramic GOS was shown to be excellent magnetic regenerator material. Published under licence by IOP Publishing Ltd doi:10.1088/1742-6596/897/1/012010
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