Abstract: The origins of the magnetic anisotropy energies of the crystals of FeO and CoO in the state of antiferromagnetic ordering and the mechanism of the deformation they suffer when the antiferromagnetic ordering sets in are investigated from the atomistic point of view, following the line developed in the preceding paper. It is concluded that the most effective part of the magnetic anisotropy energy in the deformation-free state of the crystals originates from orbital multipole (or van Vleck's orbital valence) interactions arising from both the coulomb and exchange interactions between cations. The deformation of the crystals, however, is caused mainly by magnetostriction arising from linearly strain-dependent terms of the crystalline field energies. It is shown that the theoretical determination of the axis and magnitude of the deformation, using the point charge model for the calculation of the crystalline field, can give results which are semi-quantitatively consistent with the experimental results. It is shown that in CoO the deformation-dependent anisotropy energy overcomes other anisotropy energies and determines the direction of the magnetization to be the direction of the tetragonal axis of deformation, [001], while in FeO the deformation-independent anisotrpy energies are predominant in determining that direction, which coincides with the crystalline trigonal axis, [111]. Discussions are also given for other kinds of deformations which do not depend on the orientation of the magnetic moments, that is, the volume striction and the trigonal deformation suggested by Greenwald and moments, that is, the volume striction and the trigonal deformation suggested by Greenwald and Smart. A brief comment is given to the magnetic anisotropies of MnO, MnS and NiO.
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