The Néel Theory of Ferrimagnetism

Abstract

The Néel theory of ferrimagnetism is a molecular-field theory of magnetic ordering in systems which contain nonequivalent substructures of magnetic ions. The two principal results of the theory are (a) the curve of reciprocal susceptibility vs temperature above the Curie temperature is an hyperbola, and (b) the curve of spontaneous magnetization vs temperature below the Curie temperature may have any one of a number of unusual forms. The exact form depends on the distribution of magnetic ions between the substructures and on the relative values of the molecular field coefficients. The agreement between the predictions of the Néel theory and some experimental observations on ferrites is discussed briefly.

Effect of ZrO2 addition on the microstructure and electromagnetic properties of YIG

“…As to saturation magnetization, it increases with ZrO 2 addition increasing and reaches the maximum of 1936 × 10 −4 T at x = 0.3, which is followed by a decrease when x is 0.4. Based on Neel's theory of ferrimagnetism in ferrites [25], the substitution of a non-magnetic ion like Zr 4+ in [a] site can lead to the rise of total saturation magnetization. However, the observed decline in saturation magnetization for the sample with x = 0.4 may be attributed to the formation of a special d site when the addition of Zr 4+ surpasses a critical limit (x = 0.3), in which all the magnetic positive ions will lose the object of superexchange interaction because of the position occupied by Zr 4+ .…”

Isotropic, high coercive field in melt-spun tetragonal Heusler Mn3Ge

“…16 A detailed study of the Néel theory of ferrimagnetism was first given in 1955 by Smart. 32 A possible explanation for the P-type ferrimagnetism of Mn 3 Ge is the different behavior of the two magnetic Mn species on the 2b and 4d sites. Assuming that the magnetic moment on the 4d site is less sensitive to thermal activation than that of Mn on the 2b site, a resulting increase in the total moment would result, which is the characteristic of P-type ferrimagnetism.…”

Effect of Bi3+ Ion Substitution on Magnetic Properties of Cobalt Nano Ferrites Prepared by Sol-Gel Combustion Method

“…It is observed that, the magnetic properties such as saturation magnetisation (Ms), remnant magnetisation (Mr) and coercivity (Hc) values are gradually decreasing with the increase of bismuth ion concentration and the values are listed in [28]. This is due to the cation distribution in between A and B sub lattices which were proposed by Neel's two sub lattice model [29] [30]. According to this, in any ferrite the magnetic order of tetrahedral clusters (A-site) and octahedral clusters (B-site) was found to be anti parallel to each other.…”