For 10 points, identify this technique in which a change of the B-field at constant entropy results in a cooling.
The balloon-borne CMB experiment TopHat uses ferric ammonium alum in its implementation of this technique, which was first developed fully by William Giauque. In 1997, gadolinium alloys were used to discover a giant version of the effect which makes this technique possible, and in 2000, that same effect was discovered in Heusler alloys. The most common cycles utilized in this technique are the AMR, Ericsson, and Stirling cycles, and the effectiveness of this technique is limited by Nernst's Equation. Devices employing this technique typically utilize a salt pill with a high magnetic moment and the theory of this technique is derived by adding a B-dM term to the thermodynamic relation. For 10 points, identify this technique in which a change of the B-field at constant entropy results in a cooling.
The balloon-borne CMB experiment TopHat uses ferric ammonium alum in its implementation of this technique, which was first developed fully by William Giauque.
adiabatic demagnetization [or magnetocaloric effect]