Ferrimagnetic Resonance Relations For Magnetocrystalline Anisotropy In Cubic Crystals

A general resonance equation which directly relates the resonance frequency to the static applied field and internal anisotropy field for cubic ferrimagnets was derived. The equation is valid for an infinite number of planes which contain the 110 direction. The limitations and difficulties of other approaches outlined in the literature are mentioned. The advantages and disadvantages of the derivation contained in this thesis are explained. Certain interesting features of the resonance relationship are mentioned. The theoretical calculations give very close agreement to the experimental observations on yttrium iron garnet (YIG), as well as gallium- and indium-substituted YIG's. The theoretical calculations, however, increasingly deviate from experimental results as the internal anisotropy fields increase. The validity of Wojtowicz's remarks concerning the inaccuracy, incompleteness, and confusion of the literature is investigated. (Author).

A study of single-crystal ferrimagnetic crystals at microwave frequencies was conducted. The parallel pumping technique was used to experimentally measure spin-wave line width, magnetoelastic coupling constants, energy exchange constants, and phonon linewidths. The experiments were carried out at 300K, 194K, 77K, and 4.2K at X- and K-band frequencies. Four samples of pure, single-crystal yttrium iron garnet (one disk, and three spheres) were extensively investigated. Conditions for optimum detection sensitivity of spin-wave instability measurement are given and discussed. The theory of parallel pumping is explained and worked out in detail. Expressions are obtained for spin-wave and phonon linewidths, magnetoelastic constants and exchange constants in terms of experimentally measured quantities. A literature search was made for publications dealing with parallel-pumping phenomena. These articles (over 75) are abstracted for their contents relative to this investigation. (Author).

Measurements of the temperature dependency of firstand second-order anisotropy fields, as well as g-factors, have been made on single crystal iron garnets of yttrium, lutetium, gallium-yttrium, and indium-yttrium. Unit formulas are denoted by Y3Fe5O12, Lu3Fe5O12, YeFe(5-z) Ga(z)O12, and Y3Fe(5-z)InzO12, respectively. Results show that at any given temperature, first-order anisotropy fields within the yttrium iron garnet are enhanced by the substitution of gallium and diminished by the substitution of indium, and that for any given sample, these fields increase as temperature is lowered. Low temperature anisotropy fields for lutetium iron garnet, while completely at variance with those previously reported, are as expected. However, the anisotropy surface of lutetium iron garnet is highly convoluted at liquid helium temperatures. Also, there is evidence that anisotropy fields are independent of sample size effects. No experimental evidence of effects due to an external electrostatic field or of thermal hysteresis could be detected. Secondary peaks observed superimposed on the principal resonance absorption curve of some of the samples over many temperatures are noted. Derivations are given of the cubic system anisotropy energy and Kittel's 'effective demagnetization factors' in the (110) plane up to third order. (Author).

A general description of AFCRL's new 29-ft parabolic antenna is given. This antenna, designed for operation at 35 Gc, has Cassegrain feed optics and a precise reflecting surfdce supported on an elevation over azimuth mount. Design parameters include a gain of 67.5 dB at 35 Gc and a pointing capability of better than =1 arc min under 30-knot wind loads, normal solar loading, and peak accelerations of .012 deg/sq sec. The servo system was designed primarily to track objects traveling at sidereal rates. A limited satellite tracking capability should exist, however. Emphasis is given to engineering aspects of the tower, mount, drive system, and reflector assembly which should provide efficient rf operation and extreme precision in pointing. (Author).

The tables present the results of computations of the intensity and the degree of polarization of sky radiation and radiation scattered by a unit volume of air containing natural aerosols. The tabulated data are based upon new values of the scattering functions i sub 1 and i sub 2 and the scattering cross sections k, derived using the Mie theory with m = 1.5. In the case of primary scattering of radiation, the results are valid for a turbid atmosphere. The tables of the scattering coefficients and optical thickness, the absolute scattering functions, the intensities, and the degrees of polarization are computed for various wavelengths between 0.4 and 1.2 microns and for discrete scattering angles between 0 degrees and 180 degrees. Aerosol size distributions of the form dn(r) = c.r/v dlogr, with v = 2.5, 3.0, and 4.0, are assumed. The lower and upper limits for the size range were chosen as r sub 1 = 0.04, 0.06, and 0.08 micron and r sub 2 = 3, 5, and 10 microns respectively. (Author).