Demagnetization cooling of a Chromium cold gas

This paper reports on the first experimental realization of demagnetization cooling in a gas. In the presence of an external magnetic field, particles with a permanent magnetic dipole moment try to minimize their energy by aligning their dipole along the field, thus generating a macroscopic magnetization of the material. If the field is reduced enough, the particles are able to change their orientation and to do magnetic work during such a demagnetization process. This is done at the expense of their kinetic energy, with a consequent reduction of the temperature of the system. So far such a process has not been detected in gases because at low density the rate of demagnetization is very low. But Cr atoms have such a large magnetic dipole moment (6 mu_B) that for experimentally accessible densities of 10¹³ atoms/cm³ and sufficiently low fields (around 250 mG), they can demagnetize on a timescale of a few seconds.