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On the Adiabatic Demagnetization of Iron Alum
Phys. Rev. 64, 94 – Published 1 August, 1943
DOI: https://doi.org/10.1103/PhysRev.64.94
Abstract
The behavior of iron alum during adiabatic demagnetization to temperatures near the absolute zero is of particular theoretical interest because of the deviations from Curie's law that arise from the perturbing actions of crystalline field and magnetic dipole-dipole coupling. The effect of these perturbations on the magnetic moment and the entropy is calculated exactly to second-order terms in the magnetic coupling and to third-order terms in the crystalline potential. The calculations are presented for crystalline fields of either cubic or axial symmetry and are valid for the case of large applied fields in which saturation effects become important. Theoretical values of the adiabatic moment are found to be in satisfactory agreement with the experimental values determined by Casimir and de Haas. A true thermodynamic scale is established that enables the temperature to be calculated at any value of the magnetic field during demagnetization. The relationship of this scale to the temperatures determined by the magnetic method of de Haas and Wiersma is discussed.
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