Adiabatic Demagnetization Temperatures Below

Adiabatic demagnetization has been historically the first method which allowed to reach temperatures below 1K. It was proposed in 1926 by P. Debye and W.F. Giauque and converted into a practical realization by W.F. Giauque and D.P. MacDougall in 1933. 

Magnetic thermometry has been developed chiefly to measure temperatures near absolute zero (below -458°F, or -272°C). These measurements are obtained by adiabatic demagnetization of a paramagnetic salt. Inductance can be measured with an AC bridge (as shown in Figure 3.164) whose balance is independent of frequency. The relationship between self-inductance and sus-... 

Roinel et al. (1985) have made a detailed study of the relaxation rates for the enhanced Tm (/ = ) nuclear spins as a function of temperature from 0.05 up to 2 K, in fields up to 4 T perpendicular to the c-axis. The variation of the relaxation rate is rather complex at 50-100 mK recovery is generally non-exponential. At fields below 0.5 T, relaxation is dominated by interactions with electronic impurities, but above 1T effects are attributed to a bottle-neck between phonons and bath. It is concluded that the relaxation rate at low fields would be too short to allow study of a nuclear ordered state, produced by adiabatic demagnetization of the enhanced Tm nuclear spins. 

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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