The basic operating principle of an ADR is the use of a strong magnetic field to control the entropy of a sample of material, often called the "refrigerant." Magnetic field constrains the orientation of magnetic dipoles in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, and this corresponds to lower entropy and heat capacity because the material has (effectively) lost some of its internal degrees of freedom. If the refrigerant is kept at a constant temperature through thermal contact with a heat sink (usua ...
Adiabatic demagnetization - Paramagnetic salts.
The simplest choice of refrigerant is a sample of a paramagnetic salt, such as cerium magnesium nitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.
In a paramagnetic salt ADR, the heat sink is usually provided by a pumped 4He (~1.2 K) or 3He (~0.3 K) cryostat. An easily attainable 1 Tesla magnetic field is generally required for the initial magnetization. The minimum temperature a ...
