Kevin D. McKinstry

Low power nonlinear effects in the ferromagnetic resonance of yttrium iron garnet

Ferromagnetic resonance (FMR) absorption was observed in a spherical single‐crystal sample of Y3Fe5O12 (YIG) at 9.5 GHz and room temperature. Resonance absorption curves were obtained as a function of microwave power level and duty cycle for different static field directions relative to the crystal axes. Foldover effects and other nonlinear behavior were seen at microwave field amplitudes (hrf) between 9 and 50 mOe with the applied static field in the (110) plane. When FMR absorption is observed with a high power cw signal (hrf=50 mOe) with the biasing field along either the [100] or the [110] directions and decreasing in magnitude, an absorption curve is obtained that has a long broad shoulder which is shifted below the low power FMR biasing field position. With increasing field in these directions, the absorption curve develops a cusp below the low power biasing field position. With the bias field in the [111] direction the absorption curve shows cusps for both increasing and decreasing fields at this p...

High‐field effective linewidth and eddy current losses in moderate conductivity single‐crystal M‐type barium hexagonal ferrite disks at 10–60 GHz

The losses associated with the high‐field tail region of the ferromagnetic resonance (FMR) absorption curve were investigated at 10, 19, 35, and 60 GHz for 0.10–1.75‐mm‐thick c‐plane circular disks of flux‐grown single‐crystal M‐type barium ferrite materials. A conventional high‐field effective linewidth analysis of the data yielded an effective linewidth which increased with the square of the disk thickness and linearly with frequency, dependencies which indicate a predominant eddy current loss process. Based on these results, an eddy current loss analysis of the tail region was done, based on the insulator FMR response and eddy current losses driven by the FMR response. This analysis leads to a new noninvasive technique for the determination of the microwave conductivity in moderate conductivity ferrites. One obtains the conductivity from an appropriate analysis of the FMR absorption tail in the same way that analysis of the magnetic loss tail yields a high‐field effective linewidth. Based on this techn...

Methods for determination of microwave cavity quality factors from equivalent electronic circuit models

Simple analytic methods have been developed for high‐accuracy measurement of the quality factor Q of reflection and transmission microwave cavities. These methods are based on the consideration of cavity equivalent electronic circuit models and use measured cavity parameters over a narrow frequency range spanning the cavity resonance frequency to determine the Q factor. Since only straightforward frequency and power measurements are necessary, these methods are well suited to computer‐aided data acquisition and analysis. Specific results are presented for a standard X‐band reflection cavity with a Q of 2699.1±0.5 and a high‐Q X‐band cylindrical cavity with a Q of 23112±4.

HIGH FIELD EFFECTIVE LINEWIDTH AND EDDY CURRENT LOSSES IN MODERATE CONDUCTIVITY SINGLE CRYSTAL ZN-Y HEXAGONAL FERRITE AT 10-35 GHZ

The microwave losses associated with the extreme high field tail region of the ferromagnetic resonance (FMR) absorption curve for 0.08‐ to 1.38‐mm‐thick c‐plane circular disks of single crystal Zn‐Y hexagonal ferrite materials with planar anisotropy were investigated at 10, 19.3, and 35.3 GHz, with the static external magnetic field applied in plane. Analysis of the data in terms of magnetic losses only gave anomalous high field effective linewidth ΔHF results; this ΔHF showed a substantial increase with the field, changed with both disk thickness and radius, and was higher for an out‐of‐plane microwave field direction than for an in‐plane direction. This linewidth did scale with the square of the disk thickness, one indication of predominant eddy current losses. The data were then analyzed in terms of eddy current losses, based on the assumption of an insulator FMR response and a high field eddy current loss absorption tail driven by that response. The predictions of the model were in good agreement with...

Off resonance loss measurements in ferrites at 35 GHz

The effective-linewidth technique at 35 GHz has been applied to polycrystalline YIG and single crystal Zn/sub 2/-Y hexagonal ferrite with planar anisotropy. Because of static field limitations, it was necessary to use low-field rather than high-field extrapolations to obtain the baseline cavity parameters for the loss determinations. The results show that the low-field off-resonance effective linewidth of these materials is 12 Oe for YIG and 30 Oe for Zn/sub 2/-Y. The results are consistent with estimated values of the intrinsic losses in these materials. >

Effective linewidth due to conductivity losses in barium ferrite at 10 GHz

The effective linewidth technique has been applied at 10 GHz and room temperature to single-crystal barium ferrite with uniaxial anisotropy. Effective linewidths were obtained from measurements of the positive field tails of the FMR (ferromagnetic resonance) absorption and dispersion curves for circular disks of barium ferrite ranging in thickness from 0.33 to 1.75 mm. The effective linewidths ranged from 125 to 2850 Oe, and vary linearly with the square of the disk thickness. This linear relation is consistent with an eddy current loss process. A fit of the data to rudimentary eddy current theory yields a resistivity of 0.8 Omega -cm. This result for the resistivity is consistent with a resistivity of 1-4 Omega -cm determined from 10-GHz dielectric measurements and 20 Omega -cm from DC resistivity measurements. The effective linewidth vs sample thickness extrapolated to zero thickness indicates an intrinsic linewidth of 60+or-45 Oe. The results indicate that, for barium ferrite samples thicker than about 0.3 mm, the effective linewidth losses are dominated by losses due to eddy currents in the material. >

Predictive analysis of linewidth parameters of microwave garnets

Abstract The linearity of microwave parameters—resonance linewidth ΔH and effective linewidth ΔHeff—is demonstrated and its use in the CAD/CAM of new microwave garnets proposed. Such an approach would combine a numerical database of microwave data and several computational programs. This paper complements the discussion of the magnetic properties of microwave materials and their CAD/CAM in R. Puflea-Ramer et al., Electr. Power Syst. Res., 24 (1992) 141–148.

Microwave effective linewidth in thin metal films

An effective linewidth technique for characterizing microwave losses in thin ferromagnetic metal films, similar to the technique for ferrites, has been developed. The extension to metal films is nontrivial. A numerical solution of the electromagnetic boundary value problem for the fields inside the film must be used to evaluate the on‐ and off‐resonance losses, and these calculated losses must be directly related to changes in the microwave cavity Q on an absolute scale. Specific measurements and analyses were done for polycrystalline permalloy on glass. Measurements at 10 GHz yield a change in 1/Q with field which is in accord with theory and can be modeled off resonance to obtain intrinsic losses. The analysis yielded an intrinsic Landau–Lifshitz damping parameter of 5.5×107 rad/s for permalloy. This corresponds to a half‐power effective linewidth of 27 Oe, which is comparable to the best published 10 GHz linewidth for single‐crystal iron films.

High field effective linewidth due to conductivity losses in Zn2Y hexagonal ferrite at 10, 20, and 35 GHz (abstract)

A simple technique to analyze the effective linewidth at high field, corresponding to the far field tail of ferromagnetic resonance (FMR) absorption, was recently reported. This technique has now been applied at 10, 20, and 35 GHz to single crystal Zn2Y hexagonal ferrite with planar anisotropy. Far field effective linewidth (ΔHeffFF) measurements were made for a series of 2–3 mm‐diam, 0.08–1.33‐mm‐thick c‐plane disks. The ΔHeffFF is taken to represent the intrinsic linewidth, in the sense that there are no two magnon or inhomogeneous linebroadening contributions to the losses on the far‐field FMR tail. ΔHeffFF at each frequency increases with the square of the disk thickness. This increase is consistent with an eddy current loss process. A fit of the data to a simple eddy current model yields resistivities of 10.3, 9.7, and 8.3 Ω cm at 10, 20, and 35 GHz, respectively. These values are consistent with a resistivity of 2 Ω cm from 10 GHz dielectric measurements and 20 Ω cm from the resistivity measurements...

Modification of a Princeton Applied Research FM‐1 vibrating sample magnetometer

A Princeton Applied Research model FM‐1 vibrating sample magnetometer (VSM) has been modified using lock‐in detection, automatic data acquisition, and microcomputer control. The practical sensitivity in the updated version has been improved to 10−4 emu. Data collection and data management are quicker and greatly simplified. Through menu driven software and modular design, the overall ease of use has been enhanced. The original layout of the FM‐1 has been retained so that no versatility is lost for either the original or modified version.