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Gamma ray anisotropies in antiferromagnetic crystals of MnSiF₆.6H₂0 and CoC1₂.6H₂0 Griffiths, David J.

Abstract

By the technique of adiabatic demagnetization, paramagnetic salts may be cooled to temperatures less than .1°K. By good thermal contact between crystals and paramagnetic salts, the antiferromagnetics MnSiF₆.6H₂0 and CoC1₂.6H₂0 were cooled to temperatures at which the hyperfine interaction energy of an introduced Mn⁵⁴ impurity was comparable to kT. This resulted in a preferential population distribution of the available energy states. The alignment of nuclear spin, induced by the crystalline field present at the active Mn⁵⁴ impurity, was measured by the anisotropic distribution of the ƴ-rays given off by the radioactive Mn⁵⁴. This data led to a determination of the crystalline field acting on the impurity ion in MnSiF₆.6H₂0 and to verification of theoretical calculations representing the anisotropy of ƴ-emission as a function of absolute temperature. Also by means of such data, a determination was made of the axes of alignment in the antiferromagnetic, CoC1₂.6H₂0 .

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