Temperature adiabatic demagnetization

Using liquid helium, Kurti and co-workers and others, have succeeded in obtaining temperatures of a few microkelvins by the adiabatic demagnetization of copper nuclei. 

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. 

The third law is concerned with the nature of entropy (Sidebars 5.10-5.13) and thermodynamic behavior in the limiting approach toward T = OK. Although Joule-Thomson expansion (Section 3.6.3) is a useful refrigeration technique down to about 20K (7J for H2), more specialized cryogenic techniques are required to approach the sub-microkelvin (around 10 6K) domain of extreme low temperatures. The most important such technique, adiabatic demagnetization, is described in Sidebar 5.16. 

At low temperatures (dxM/dT)PnH is large and negative, so the value of the derivative (dT/8H)SPn is positive, i.e., the temperature decreases with an isentropic decrease of the field strength. This equation provides the basis for the attainment of low temperatures by adiabatic demagnetization. 

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-... 

Early observations of calcium in the solid state used either double resonance178 in CaF2 or adiabatic demagnetization at low temperature.179 H-43Ca CP was one of the first experiments that reported more conventional NMR spectra.180 CP used a 46 kHz spin-locking field on the protons that was matched to the central transition of the calcium. Optimum CP was achieved with a contact time of... 

The integration may be carried out once c and aQ are specified in their dependence on T and E0 this yields the alteration of temperature as the electric field is turned on adiabatically at constant volume. This matter will not be carried beyond this point because a completely analogous case will be handled in Section 5.8, under the heading of adiabatic demagnetization. 

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