ECAUSE nickel-zinc ferrites give a good magnetic response a t B high frequencies, they have been extensively investigated' for applications in various electronic devices, particularly for communications systems. Stuijts et al. measured initial permeability, resistivity, and density for nickel-zinc ferrites as a function of composition.In the present study, the coercive force, the initial permeability, and the saturation magnetization of nickel-zinc ferrites were measured for six compositions with a constant Ni/Zn ratio of 0.47; the Fe content varied from Fe-deficient to Fe-rich with respect t o Nio,~zZno.~Fe~04. The coercive force and saturation magnetization were correlated with the initial permeability for all compositions.The NiZn ferrite compositions were prepared by wet-mixing of oxides. Powders were calcined at 900°C, remilled, isostatically pressed into toroids l/2 in. in diameter, and sintered at 1230°C for 3 hr. The complex initial permeability, po = p' -j p', and saturation magnetization, M,, at 25 koe were measured b y standard t e c h n i q~e s .~-~ The coercive force, He, was determined from hysteresigraph traces obtained from coil wound toroids driven by 3 amp-turns a t 60 cps (-1.3 oe).The bulk density was measured by the immersion technique (ASTM B311-58); the average grain size 2, by the planimetric method (ASTM E112-61); and the lattice parameter ao, by use of Debye-Scherrer X-ray powder patterns (back reflection region). All measured data are tabulated in Table I. Photomicrographs of the compositions investigated showed that the grains were uniform. The few pores detected were confined to the grain boundaries. The densities ranged from 5.18 to 5.20 g/cm3 (about 97.5% of theoretical density). The average grain diameter was directly proportional to the mol.% Fez08. and Presented at Properties of Some Orthoferrites and Cyanides a t Low Temperatures," Phys. Rat., 103 [3] 572-78 (1956).Fig. 1. Coercivity and initial permeability vs. Fez03 content of NiZn ferrites.Figure 1 shows the variation with composition of coercivity and initial permeability at 1 Mc and 4 Mc. The curves show that the coeravity is a minimum and the initial permeability is a maximum at about 50 mol.% Fe& This behavior can be deduced froms: 2kzMa2 po = 1 + __-IKI I KI = magnitude of the effective magnetocrystalline anisotropy. M. = saturation magnetization. k is a shape-dependent constant. By eliminating IKI between Eqs. (1) and (2), we obtain: 4kM, p I l = l + --H C Since M , is constant for the compositions considered (see Tablc I), we deduce from Eq. (3) that the initial permeability is inversely R. S. Weisz, "Magnetic Anisotropy Constants of Ferroxnagnetic Spinels," ibid., 96 [3] 800-801 (1954).