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 (H⩽3 T) 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, Gd3Ga5−XFeXO12, 0.00⩽X⩽5.00) and gadolinium aluminum perovskite (GAP, GdAlO3) 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 (0.00⩽X⩽5.00), temperature (2 K⩽T⩽30 K) and applied magnetic field (0 T⩽H⩽3 T). The magnetic entropy change (ΔSmag) between 0 T and 3 T was determined from the magnetization data. In the GGIG system, ΔSmag was compositionally dependent; Fe3+ additions up to X⩽2.44 increased ΔSmag at T>5 K. For GAP, ΔSmag was similar to that of GGIG, X=0.00, both in terms of magnitude and temperature dependence at T>10 K. However, the ΔSmag of GAP at T<10 K was less than the endmember GGIG composition, X=0.00, and exhibited maximum ∼5 K.