From the measurements on paramagnetic salts, the p value deduced for Ni" is 16; while Ni+ has the same electronic con stitution as Cu" whose p value is 9; these values are calculated from the Curie constant in the expression XIV— If dif T— 0 ferent ions are present, the p value deduced will be a root mean square value. In this case there is one ion (Ni") for which p= 16, one (Ni+) for which p = 9, and three (neutral Ni) for which p= o, so that the mean value deduced from the measurements on nickel will be p= = 82.
The theoretical curve for the variation of the saturation inten sity of magnetization with temperature (fig. 34) is calculated on the basis of the classical Langevin theory, according to which the elementary atomic carriers can orientate themselves in any direc tion with respect to the applied field. On the quantum theory,
however, only certain discrete orientations should occur, the re solved magnetic moments in the field direction only having a dis crete number of possible values, as is confirmed by both indirect and direct evidence. It has been shown by P. Debye that calcu lations on this basis lead to curves which differ slightly from the theoretical curve shown and which qualitatively agree more closely with experiment.
The Weiss molecular field theory, combined with the quantum version of the Langevin theory of paramagnetism, seems to be capable of correlating satisfactorily the data, relating to the varia tion of the intensity of magnetization of ferromagnetics in strong fields with the temperature below the Curie point, and those re lating to the variation of the paramagnetic susceptibility above. In many of its aspects, ferromagnetism, in fact, is simply a spe cial case of paramagnetism, the difficulty as to the nature of the molecular field arising in connection with both. The most striking characteristic of ferromagnetics, however, is the manner in which the magnetization varies in relatively weak fields, the detailed character of which has not so far been considered.
.41311110 1111