Investigations of magne-crystallic action. Part II.-Paramagnetics

Abstract

In Part I we gave an account of some magnetic measurements on diamagnetic crystals. It is found that the diamagnetic anisotropy of a crystal can be satisfactorily explained in terms of the intrinsic anisotropy of the individual molecules (or ions) constituting it and their relative orientations. Thus by a study of the magnetic properties of diamagnetic crystals much useful information can be obtained regarding the anisotropies of molecules and their orientations in the crystal lattice. The study of paramagnetic crystals is also of great interest, but for other reasons. Here the crystal-forces play an all-important part in determining their anisotropy, as opposed to diamagnetic crystals where the influence of crystal structure is indirect, and appears only so far as it determines the relative orientations of the molecules. The recent work of BETHE on the Stark-splitting of the energy levels of a paramagnetic ion in a crystal, under the influence of the crystalline forces, and the discussions by VAN VLECK , and by PENNEY and SCHLAPP about the effect of this splitting on the magnetic behaviour of the ion, throw considerable light on the origin of the magnetic anisotropy in a paramagnetic crystal. From the point of view of these newer theories, especially in consideration of our present incomplete knowledge regarding atomic energy levels in crystals, extensive data on the anisotropies of paramagnetic crystals would be useful. The present paper describes the results of some direct measurements on anisotropy for a number of crystals.