- A system for cooling to temperatures below that of liquid helium. A strong magnetic field is used to align the spins of the molecules of a block of a paramagnetic salt which has been cooled by a liquid helium bath. The block is then isolated from the magnetic field and the helium bath. Most of the remaining heat energy is absorbed in randomizing the spins of the molecules. Readings of less than 2 millikelvins have been achieved using such devices.