YIG Rod Research Articles

Theory of two-dimensional magneto-photonic crystals using complex Fourier factorization

The plane wave expansion method for calculating magneto-photonic crystals (MPCs) is modified via complex Fourier factorization whose basic principles are briefly explained. The new approach is used to simulate the photonic band structure of a two-dimensional MPC made as Bi:YIG rods arranged with square periodicity. The considerable improvement of the convergence properties is demonstrated for selected points of the bands.

Quantitative analysis of YIG, YFeO 3 and Fe 3O 4 in LHPG-grown YIG rods

The use of higher pulling rates in the laser heated pedestal growth (LHPG) method will cause the YIG (Y 3Fe 5O 12, yttrium iron garnet) crystals thus grown to contain YFeO 3, YIG and iron oxides due to rapid solidification. In the experiment, a Verwey transition, the distinctive magnetic property of magnetite, was observed near 107 K in the grown YIG rods using a super-conducting quantum interference device (SQUID) magnetometer. Moreover, the standard relationships between the YIG and YFeO 3 weight ratios and the primary diffraction-intensity ratios of the YIG (420) and YFeO 3 (121) peaks were obtained from the XRD data by indexing the powders with their specific ratios. We also derived the weight ratios of the three magnetic compounds in the grown rods, via measuring the saturation magnetizations. From the experimental results, the iron oxide in the grown rods is also confirmed to be magnetite. This is a good analytical technique for quantifying the magnetic compounds in a material.

A Short History of Microwave Acoustics (Corrections)

In regard to Section III of the above paper, John Eshbach has brought to my attention that the original experiments on microwave magnetoelastic YIG delay lines were performed by him on disc-shaped geometries and published in 1962 . His 1963 paper gave the first details of the electromagnetic --> spin --> acoustic conversion process for a YIG disc, which is shown in Fig. 5 of the above paper for a YIG rod. Premium in space precluded a full description of the entire conversion process for an axially magnetically biased YIG rod which is electromagnetic --> magnetostatic -->spin (exchange) -->acoustic. This was originally proposed by B. Yazgan in her 1966 Ph.D. thesis submitted to Glasgow University and subsequently developed by J. H. Collins and experimentally verified by B. A. Auld et al. Reference to the caption in Fig. 5 of the above paper allows references [3] and [4] to be traced.

Experimental observation of surface modes along two parallel-axially magnetized ferrite rods

Two pairs of resonance absorptions due to the lowest-order even 1e and odd 1o surface modes along two axially magnetized polycrystalline yttrium iron garnet YIG rods of several lengths from 3 to 25 mm have been observed in an experiment where the ferrite rods were placed in a TE10 rectangular waveguide and in a cavity coupled with a current loop. One pair is 10e and 10o resonances whose magnetization in each rod precesses in phase over the rod length. The other pair is 11e and 11o resonances due to the half-wavelength standing waves along the rods. The experimental results are compared with theory. Results of a rudimentary experiment on a magnetically variable directional coupler using these modes are also presented.

YIG rod ferrite limiter with extended dynamic range

Analytical and experimental results obtained on a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</tex> -band ferrite limiter which utilizes a YIG rod inserted down the center of a coupled dielectric resonator bandpass structure are described. This device is aimed at providing receiver protection for communication systems operating in a dense, high signal power environment. By utilizing a long thin single-crystal YIG rod instead of YIG spheres, the dynamic range has been extended from 20 dB to 35 dB. The threshold power varies from 5 dBm at 4.4 GHz to 15 dBm at 5 GHz with an insertion loss of less than 1 dB.

Influence of Surface Metallization on the Propagation Characteristics of Surface Magnetostatic Waves in an Axially Magnetized Rectangular YIG Rod

It has been shown that the boundary conditions strongly influence the propagation characteristics of surface magnetostatic waves propagating in the direction of the external dc magnetic field; the frequency spectrum narrows and the cutoff wavenumber decreases continuously as the gap between the sample surfaces and metal walls increases in the direction in which the magnetic potential decays exponentially. Experimental results obtained at X band agree well with the theoretical estimates.

High-Power S-Band Junction Circulator (Short Papers)

The design of a high-power air-cooled microwave Y-junction circulator which is capable of operation at peak and average power levels of 800 kW and 800 W, respectively, is described. The unit is an H-plane waveguide circulator which is externally air cooled. The circulator design employs a full-height substituted YIG rod with a center metal pin together with boron nitride matching transformers. The circulator exhibits an insertion loss of less than 0.4 dB, isolation greater than 22 dB, and a VSWR <1.26:1 over a 400-MHz bandwidth centered at 3.3 GHz. At high-power levels, the device exhibits insertion loss of less than 0.9 dB, isolation greater than 20 dB, and VSWR <1.25:1 at an indicative frequency within the operating bandwidth.

Synchronously tuned ferrite power limiter for broad-band systems application

This investigation describes analytical and experimental results obtained on a broadband ferrite limiter at K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> band which utilizes a synchronously tuned waveguide bandpass structure. This device is aimed at providing protection for communications and electronic warfare systems over a bandwidth from 12 to 30 percent at K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> -band frequencies. The circuit consists of a series of three cavities in a waveguide transmission line, the coupling being accomplished via the irises or symmetrical inductive slits between cavities. Because of this cavity structure, the observed threshold power levels have been reduced by an order of magnitude. By utilizing a combination of single crystal YIG and lithium ferrite rods, the threshold power for limiting varies from 0.75 W at 16.0 GHz to 2.0 W at 17.0 GHz with an insertion loss of 0.9 dB.

Spin wave instabilities in an axially magnetized YIG rod

Instabilities of spin waves in an axially magnetized YIG rod are studied in the volume magnetostatic and magnetoelastic regions using a spectrum analyzer. In the magnetoelastic region, the strength of the static magnetic field at which the resonance absorption occurs decreases with increasing input microwave power. When the input power reaches a threshold value, each absorption peak shows an abrupt jump and instabilities appear with oscillation frequencies of 300 kHz to 10 MHz. Instabilities may attribute to the second-order parametric process of the volume magnetostatic waves. In the magnetoelastic region, the intensities of the spectrum in lower sidebands are much larger than those in higher sidebands. However, in the volume magnetostatic region, the intensities of the spectrum in lower and higher sidebands have nearly equal amplitudes.

Mode Separation of Magnetostatic Waves in a Cylindrical YIG Rod

Mode Separation of Magnetostatic Waves in a Cylindrical YIG Rod

Measurement of Internal Magnetic Field Distribution in Axially Magnetized YIG Rods Based on Magnetoelastic Resonance Absorption

A new method for measuring internal magnetic field in ferromagnetic rods is described. Magnetoelastic resonance is observed in longitudinally magnetized YIG rods. The separation ΔH of adjacent resonance peaks is varied with signal frequency and applied magnetic field He. It is shown the internal magnetic field is calculated from He-ΔH curves and the results agree well with the theoretical predictions previously published. The shape of axial field distribution depends on the applied external field. In the low external field region the shape is smooth, in the medium field region it becomes square and in the high field region it again becomes rather smooth, approaching Sommerfeld field.

Modes of Resonance Absorptions of Magnetostatic Waves in Axially Magnetized YIG Rods

The magnetostatic resonance absorptions for an axially magnetized single crystal of YIG rod, [110] oriented, are observed in a waveguide and a cavity at 9.45 GHz. For the applied magnetic field ranging from 2800 to 3400 Oe resonance absorptions due to the dominant and third modes are observed but the second mode is not excited. The separation of these modes is conducted by comparing the transmitted power with the reflected microwave power pattern. For the dominant and third modes the relations between the field deviation, ΔH, from the cutoff field and the standing wave number n for each absorption are in good agreement between the theoretical and experimental values in a wide range of dc magnetic field. When the entire rod is inserted into the center of a waveguide or a cavity only the absorptions due to modes associated with an odd number, n, are observed for both dominant and third modes

Absorption Spectra by Magnetostatic Spin Waves in Axially Magnetized YIG Rods

The absorptions of microwave in axially magnetized YIG rods were measured and analyzed. The absorption peaks are interpreted to be caused by magnetostatic spin waves propagating along the rod axis. The mode numbers of absorption peaks are determined by the sample shape and the value of ωs/γ-Hi(0), where ωs is the microwave angular frequency, γ is the gyromagnetic ratio, and Hi(0) is the internal magnetic field at the rod center and depends upon the applied magnetic field. In calculations of mode number and mode separation, the demagnetizing field Hd in the rod is approximated by a quadratic equation of the square of normalized position ζ. The mode separations are independent of the microwave frequency. The experimental values of the applied magnetic field at which the absorption peaks are caused coincide with the theoretical values.

A Laminar Subsidiary-Resonance Limiter (Correspondence)

An investigation of the limiting threshold in a subsidiary-resonance Iimiter was conducted. Particular attention was given to the effects of the demagnetizing factors on the limiting threshold. Demagnetization factors of 1/2 for N/sub x/ and N/sub y/, and O for N/sub z/ made it possible to achieve thresholds an order of magnitude lower than had been obtained previously. The above demagnetizing factors correspond to a long thin rod magnetized along the axis of symmetry. A limiter, utilizing alternate polycrystalline YIG rods and dielectric rods of the same dimensions for dynamic range, and alternate single-crystal YIG and dielectric rods for reduced threshold, was developed. The dielectric rods provided magnetic insulation for the ferrite material such that each ferrite rod was biased independently in order to maintain the proper demagnetizing factors. The final limiter had a threshold of 2.8 watts peak power and a dynamic range of 30 dB.

Excitation of Longitudinal Magnetoelastic Waves in Axially Magnetized YIG Rods

It is shown experimentally and theoretically that longitudinal magnetoelastic waves can be excited with an efficiency comparable to that of transverse magnetoelastic waves in an axially magnetized YIG rod whose axis is appropriately oriented relative to the crystallographic axes. In conjunction with a thin film piezoelectric longitudinal-wave transducer this could form the basis of a useful two-port device.

Measurements of Longitudinal Elastic-Wave/Spin-Wave Conversion Efficiencies in an Axially Magnetized YIG Rod

We present direct measurements of the longitudinal elastic/spin-wave conversion efficiencies in a single-crystal axially magnetized YIG rod. Past experiments were carried out on YIG rods axially magnetized along a principal crystallographic direction (for which the longitudinal splitting vanished) and were therefore limited to shear waves. To obtain nearly maximum longitudinal splitting, our experiments were performed on a single-crystal YIG rod with the symmetry axis oriented in a (100) plane, at an angle of 22.5° to a 〈100〉 axis. For this case defocusing effects can be prevented and the longitudinal critical field gradients are at least two orders of magnitude smaller than the shear gradients. Therefore for the first time we were able to measure the conversion efficiencies over a range of gradients that included the region of weak conversion. The room-temperature experiments were performed at L band frequencies using both magnetic- and acoustic-wave injection; the results are in fair agreement to the theoretical predictions of previous authors.

Magnetoelastic damping of microwave phonons in ferrite single crystals

A detailed experimental study of room-temperature magnetoelastic attenuation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> -band longitudinal phonons in obliquely magnetized [100] YIG rods is presented. Magnetoelastic anisotropy, internal magnetic field inhomogeneity, and nonsaturation effects are evidenced. The experimental results obtained are interpreted on the basis of existing theories and proposed interaction models.

NONMAGNETOSTATIC VOLUME AND SURFACE WAVE MODES ON GYROMAGNETIC YIG ROD WAVEGUIDES

Electromagnetic surface waves on a gyromagnetic single crystalline YIG rod waveguide were measured by a disturbing body technique in a surface wave resonator. Both the volume and surface-mode surface waves were measured under conditions when magnetostatic analysis is not valid. Experimental results are presented to show that important nonmagnetostatic characteristics of surface wave propagation revealed in the dispersion plot have all been verified.

SPIN-LONGITUDINAL AND SPIN-SHEAR ELASTIC WAVE CONVERSION IN AN AXIALLY MAGNETIZED YIG ROD

We report the first successful conversion of z-directed spin waves to longitudinal elastic waves (and vice versa) in an axially magnetized (z axis) single-crystal YIG rod. The conversions — carried out at L-band frequencies and room temperature — were possible because the symmetry axis of the rod was not along a principal crystallographic direction; the axis was chosen to be in a {100} plane at an angle of 22.5° with respect to a &amp;lt;100&amp;gt; direction in order to provide nearly maximum spin-longitudinal elastic wave coupling.

Magnetostatic Waves in Short, Axially Magnetized YIG Rods

We have performed cw resonance and pulse-echo measurements on magnetostatic waves in short, axially magnetized YIG rods which do, and do not, contain a turning point. The results are compared with a simple theory which includes the effects of the radial variation of the demagnetizing field. The agreement is generally satisfactory except for the magnetostatic mode spacing when the rod contains a turning point. In this latter case the agreement is only qualitative.