Paramagnetic Behavior of Ferrites Containing Two Kinds of Magnetic Ions
The Neel theory of the paramagnetic behavior of susceptibility in ferrimagnetic ferrites is extended to include materials containing two kinds of magnetic ions. The equation of state is derived for the general case of an inverse spinel containing any kind of doubly ionized material in addition to the ferric ions. This equation is found to be considerably more complicated than the original equation of Neel. Additional calculations are made for the special case wherein the doubly ionized material is Mn²⁺. This simplifies the numerical calculation without changing the general form of the solution. The final results indicate that the relationship between the exchange integrals and the paramagnetic susceptibility is too complicated to afford a satisfactory means of evaluating these integrals. A study is made of the assumptions implicit in the use of Neel's original equation for a ferrite with two kinds of magnetic ions. The results of this study indicate that these assumptions may be reasonably valid if the divalent ion is manganese, but they are not valid for any other divalent ion.