The width of the ferromagnetic resonance has been measured at 10 000 Mc/sec in polycrystalline mixed ferrites of the composition Co a Nii_ a Fe20 4 , with a between 0 and 0.04. The minimum line width is found for a=0.025 at 20°C. This, as well as the variation of line width with temperature, can be understood on the basis of known single crystal properties and the following assumptions: (a) line width is a linear function of \K\; (b) crystal anisotropy is an additive atomic property. S EVERAL papers 1-3 have been published recently on the crystal anisotropy of cobalt ferrite and of mixed ferrites containing cobalt. The points of interest here are the following: (1) cobalt ferrite has an exceptionally large crystal anisotropy and, uniquely among known ferrites, a preference for magnetization along the [100] directions (Xi>0); (2) Co+ 2 ions tend to occupy octahedral sites as do Ni +2 ions; (3) for either nickel or cobalt ferrite the anisotropy above room temperature is quite well described by a K x term alone, the magnitude decreasing smoothly to zero atjr c ; (4) the Curie temperatures of the two ferrites are nearly equal and high (about 600 °C). Under these conditions, one expects that a ferrite of the type Co a Nii_ a Fe 2 04 will have a crystal anisotropy constant Ki equal to the weighted algebraic sum of the values of the individual ferrites. In particular, a composition can be picked with Ki = 0 corresponding to a certain ao. For aa 0 , Ki>0. Moreover, since \dKi/K\dT\ is greater for cobalt ferrite than it is for nickel ferrite, one expects the following qualitative behavior of Ki of the mixed ferrite as a function of temperature: (a) a<
The K-band microwave spectrum of sulfur dioxide has been reinvestigated with results which are in agreement with the main points of the previously reported analysis by Dailey, Golden, and Wilson. Some additional lines have been assigned, and new rotational constants have been derived which permit considerably closer agreement between observed and computed frequencies. From two of these the structural parameters r(S–O) = 1.432A and ≰ (O–S–O) = 119.53° can be obtained. The remaining discrepancy (of the order of 15 mc for ten lines involving J values up to J = 35) has been attributed to inaccuracies in the centrifugal distortion computation.
A number of garnets including yttrium garnet, Y3Fe5O12, and mixed garnets of the forms (Y1−αSmα)3Fe5O12 and (Y1−βGdβ)3Fe5O12 have been prepared. X-band ferromagnetic resonance and saturation magnetization have been measured as a function of temperature. At room temperature samarium substitution for yttrium produces an approximately linear increase of line width with samarium content with practically no change in magnetization. Gadolinium substitution, on the other hand, has a much smaller effect on line width but produces an approximately linear decrease in saturation magnetization. Possible microwave application of these materials are discussed.
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