How does an Adiabatic Demagnetization Refrigerator Work ?
An Adiabatic Demagnetization Refrigerator (ADR) works by using the properties of heat and the magnetic properties of certain molecules. Some molecules have large internal magnetic fields, or “moments”. Just like a tiny bar magnet, these molecules will align themselves with an external magnetic field. The random thermal motions of the molecules, on the other hand, tend to de-align them. The higher the temperature, the more they de-align. ADRs generally use certain types of salts for the molecules, because they have particularly large magnetic moments. The salt is contained in a cylinder, usually called a “salt pill”. This salt pill is thermally connected to the object we want to cool (our X-ray detectors, for example) Suppose the salt pill is first placed in a strong magnetic field. The molecules align with the external magnetic field, and the magnetic energy of each molecule is minimal. If the strength of that field is decreased, then the thermal motion of the molecules starts to twist
