Demagnetization, adiabatic

Figure A2.1.11. Magnetic cooling isothemial magnetization at 4 K followed by adiabatic demagnetization to 0.04 K. (Constructed for a hypothetical magnetic substance with two magnetic states with an energy...

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. 

Figure 4.15 Schematic of the experimental setup used in an adiabatic demagnetization experiment.

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. 

Fig. 7.7. Entropies S (divided by the gas constant R) versus T of four salts used in adiabatic demagnetization in zero field (full lines) and in 2 T (dashed lines) [22]. 

Commonly used salt for adiabatic demagnetization refrigerator... 

The paramagnetic salts useful for this type of thermometry are the same as that used in the ADR (adiabatic demagnetization refrigerator, see Section 7.3 and Fig. 7.7). The most commonly used salts are ... 

For example in copper, a metal used in nuclear adiabatic demagnetization (see Section 7.4), electron and phonon systems are decoupled the power transferred between the two systems is [18] ... 

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. 

Thus, repeated cycles of isothermal magnetization and adiabatic demagnetization lead to the desired cooling of the salt. 

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. 

Figure 1 (a) Adiabatic demagnetization (b) adiabatic demagnetization in agreement... 

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