By Adiabatic Demagnetisation

This process was given independently by Debye (1926) and Giauque (1927). The process is based upon the principle that when a magnetized body is demagnetized adiabatically (i.e. in such a way that heat can neither enter nor leave the system) the temperature of body must fall. When a suitable solid is magnetised the order is increased, since various magnetic entities are aligned. When demagnetisation is allowed to occur, the disorder returns and therefore the entropy increases. Heat must be absorbed and the cooling of the substance and its surroundings results. Now-a-days, the lower temperatures are commonly attained by this method.