The behaviour of the paramagnetic ions in the single crystals of some similarly constituted salts of the iron group of elements II. Hydrated Ni 2+ salts

Abstract

In the present part of the paper, the magnetic anisotropy behaviour of seventeen similarly constituted hydrated Ni 2+ salts have been studied by the refined methods described in part I of this paper. In contrast with the similar Cu 2+ salts in part I, the Ni 2+ salts have much smaller anisotropy and their temperature variation has a much larger departure from the Curie law as predicted by theory. It is also found that, in general, the two nearly equal ionic susceptibilities denoted by K ⊥ are greater than the third denoted by K ǁ , unlike the Cu 2+ salts of part I. In Ni 2+ salts the crystalline and the ionic magnetic axes change their directions with temperature, though much less than some of the Cu 2+ salts. The coefficients in the theoretical equation for anisotropy are shown to be nearly as much structure and temperature sensitive as in the Cu 2+ salts, in some cases. The anisotropic field coefficients related to the tetragonal orbital and spin splittings of the energy levels are calculated. The variation of these from salt to salt may be as large as 100% and with temperature 12%, in extreme cases. The general behaviour of the true alkali metal double salts is in marked contrast with, and appears to be intermediate between, those of the ammonium and thallium double salts and the two single salts. The spin-orbit coupling coefficient in crystals, calculated from the temperature variation of the anisotropy, comes reasonably close to the value –324 cm -1 for the free Ni 2+ ion, whereas, from the room-temperature value of the anisotropy and paramagnetic resonance data it is found to be about 13% lower. This difference is ascribed to the inclusion of the ‘covalency factor’ of about 0·87 in these Ni 2+ salts, in the latter calculation.