Rare-earth garnets and perovskites for space-based ADR cooling at high T and low H

Future NASA satellite detector systems must be cooled to the 0.1 K temperature range to meet the stringent energy resolution and sensitivity requirements demanded by mid-term astronomy missions. The development of adiabatic demagnetization refrigeration (ADR) materials that can efficiently cool from the passive radiative cooling limit of 30 K down to sub-Kelvin under low magnetic fields (3 T or less) would represent a significant improvement in space-based cooling technology. Governed by these engineering goals, our efforts have focused on quantifying the change in magnetic entropy of rare-earth garnets and perovskites. Various compositions within the gadolinium gallium iron garnet solid solution series (GGIG) and gadolinium aluminum perovskite (GAP) have been synthesized via an organometallic complex approach and confirmed with powder x-ray diffraction. The magnetization of the GGIG and GAP materials has been measured as a function of composition, temperature, and applied magnetic field. The magnetic entropy change between 0 T and 3 T was determined from the magnetization data. (Author)