Gadolinium sulfate octahydrate

Many of the rare-earth compounds are strongly paramagnetic. Crystalline compounds of gadolinium, especially gadolinium sulfate octahydrate, Gd2(S04)3 8H20. arc used in the magnetic method of obtaining extremely low temperatures. 

Giauque s best-known accomplishment is his invention and exploitation of cooling to very low temperatures by adiabatic demagnetization. In 1924, he learned of the unusual properties of gadolinium sulfate octahydrate at the temperature of liquid helium. In his Nobel Lecture, he said ... 

The technique of adiabatic demagnetization can be used to obtain temperatures below 1 K. This method, suggested by Peter Debye in 1926 and independently by William Giauque in 1927, requires a paramagnetic solid in which ions with unpaired electrons are sufficiently separated that at 1 K the orientations of the magnetic dipoles are almost completely random. Gadolinium(III) sulfate octahydrate, Gd2(804)3 8H2O, is commonly used. 

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