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adiabatic demagnetization

A technique for cooling a paramagnetic salt, such as potassium chrome alum, to a temperature near absolute zero. The salt is placed between the poles of an electromagnet and the heat produced during magnetization is re­moved by liquid helium. The salt is then isolated thermally from the sur­roundings and the field is switched off; the salt is demagnetized adiabati­cally and its temperature falls. This is because the demagnetized state, being less ordered, involves more en­ergy than the magnetized state. The extra energy can come only from the internal, or thermal, energy of the substance.