Recent progress in magnetic refrigeration has been reviewed. Adiabatic demagnetization refrigerators (ADR) are under development at NASA for large deployable reflectors and X-ray spectrometers. The refrigerators provide temperatures of 2K at 0.027W for 165s and 0.1K at 0.01W for 13h using gadolinium gallium garnet and paramagnetic salt crystals. The Gas-Gap heat switch is used for the isothermal portion of a Carnot cycle. Active magnetic regenerator (AMR) cycles have the advantage of the Carnot cycle for larger temperature span and refrigeration capacity, in particular, above 20K. A test apparatus of the AMR demonstrated that the refrigeration capacity of 1.5-3.5W was obtainable at the temperature spans of 13-25K with a Carnot efficiency of 42%. Practical applications of magnetic refrigeration are also described.
Quantum nucleation is considered a general mechanism to explain first-order phase transition at sufficiently low temperatures. In order to obtain unambiguous evidence of the phenomenon, many attempts have been made both experimentally and theoretically. After giving a general survey of investigations with liquid helium, we present the results of our experimental studies related to the nucleation phenomenon in supersaturated 3He-4He mixtures of the dilute phase.