Contains research objectives and reports on six research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104)United States Air Force (Contract F19628-79-C-0047

Bhattacharjee, Tushar

Fishman, Daniel

Itano, Leslie M.

Kyhl, Robert L.

Morgenthaler, F. R.

Stancil, Daniel D.

Vlannes, Nickolas P.

Zeskind, Dale A.

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XIII. MICROWAVE AND QUANTUM MAGNETICSAcademic and Research StaffProf. F.R. Morgenthaler Dr. T. BhattacharjeeProf. R.L. Kyhl D.A. ZeskindGraduate StudentsD. Fishman L.M. Itano D.D. StancilL. Hegi N.P. VlannesF.R. MorgenthalerOur objective is to develop an understanding of magnetostatic and magneto-elastic wave phenomena and to employ them to create novel device concepts usefulfor microwave signal-processing applications.Several years ago, work at M.I.T. by Zeskind and Morgenthaler, and subse-quently, Cooley proved the feasibility of efficiently coupling, with microstriplines, to very high-Q tunable microwave resonances in rectangular slabs and disksof single-crystal yttrium iron garnet (YIG).Our interpretation of these resonances (potentially useful for microwave fil-tering) is that localized magnetic-mode patterns are formed in which the resonantenergies are guided or confined by regions of dc magnetic-field gradient within thecrystal. In the first experiments such gradients arose naturally from the nonuni-form-shape demagnetizing fields; in subsequent work, we have created prespecifiedgradients with shaped pole pieces designed by field-synthesis techniques.This work has two motivations. First, we want to learn whether or not it isfeasible to create a multiplicity of tunable, high-Q resonances within the samecrystal, whether all at the same frequency or separated by preset amounts. Such astructure could serve as an integrated magnetostatic filter circuit. Second, re-newed interest in magnetostatic waves for signal-processing applications in thefrequency ranges above L-band (where surface acoustic wave (SAW) device fabricationis difficult) has prompted us to inquire whether frequency dispersion, group veloc-ity, and mode energy distribution can be controlled in a practical manner.PR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)1. MAGNETOSTATIC MODES BOUND BY DC H-FIELD GRADIENTSJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)United States Air Force (Contract F19628-79-C-0047)Frederic R. Morgenthaler, Robert L. Kyhl, Tushar Bhattacharjee,Dale A. Zeskind, Daniel D. StancilOur interest in controlling magnetostatic waves and modes by means of dc fieldgradients dates from the experimental observation of localized high-Q resonancein single-crystal yttrium iron garnet (YIG) reported by Zeskind and Morgenthaler. 1These and subsequent experiments have recently been reviewed in an invited paper2presented at the Third International Conference on Ferrites held September 29-October 2, 1980 in Kyoto, Japan. We also have extended our previous theoreticaltreatment3 of two-dimensional magnetostatic modes of single-domain thin ferritecircular disks or annular rings, when the dc magnetic field is normal to the planeand varies radially.In the absence of a radial gradient, all of the modes of a solid disk havecircularly polarized rf h-fields with zero volume divergence. These modes arestrongly influenced by the magnetic pole distribution on the edge of the disk andthe rf energy becomes progressively concentrated near the rim as the mode indexincreases.The volume divergence of certain modes can change so dramatically that selec-tive localization or expulsion of the energy occurs. The sense of polarization canalso reverse. In certain cases, the volume divergence of the rf magnetization canbecome infinite (in the lossless-exchangeless approximation) at a certain interiorradius, rx. The magnetic pole distribution at this "virtual-surface" thus resem-bles that of a true surface and can serve to guide and localize the mode.Such modes have now been reanalyzed in terms of the polarization factor of therf magnetization. Analytic solutions of that factor are continuous through the"virtual-surface" and are given for the two-dimensional modes associated withspecial field profiles. Consideration of the radial impedance vs dc field planeprovides a great deal of insight into the character of both boundary-dominated andgradient-dominated modes.PR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)The rf field patterns for a typical mode are shown in Fig. XIII-1 in whichthe "virtual-surface" is shown as a dotted circle. All three fields rotate syn-chronously at the mode frequency.(a) n-field locus (b) h-field locus(c) b-field Inc,,Fig. XIII-1. Loci of m-, h-, and b-field lines for the lowest order"virtual-surface" mode when Hz(r)/M = 0.3 + 1.095 (r/R)4All patterns rotate at the mode frequency w. The "virtual-surface" (shown dotted) occurs at r/R = 0.385.Notice that the rf magnetization reverses direction in passing through thecritical radius constituting, in effect, a "microwave domain" with a 180-degreerf "domain wall."The role of exchange at a "virtual-surface" has been discussed by Morgenthaler 4PR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)and recently by Stancil 5 in a paper presented at the 1980 Intermag Conference heldin Boston during April. The effects of magnetic loss on the spin-wave componentof the mode potential and the effect on the overall mode pattern have also beentreated.6In the absence of both exchange and loss, the magnetostatic potential has alogarithmic singularity at the critical radius. Consequently, the radial h-fieldand tangential E-field will there become infinite. Either exchange or loss willremove the singularity. The cusps in the b-field are similarly removed makingfinite all the rf fields and energy densities.References1. D.A. Zeskind and F.R. Morgenthaler, "Localized High-Q Ferromagnetic Resonancein Nonuniform Magnetic Fields," IEEE Trans. on MAG, Vol. MAG-13, No. 5, Sep-tember 1977.2. F.R. Morgenthaler, "Novel Devices Based upon Field Gradient Control of Magneto-static Modes and Waves," 3rd International Conference on Ferrites, Tokyo,Japan, September 29-October 2, 1980.3. F.R. Morgenthaler, "Bound Magnetostatic Waves Controlled by Field Gradients inYIG Single Crystals and Epitaxial Films," IEEE Trans. on MAG, Vol. MAG-14,September 1978, pp. 806-810.4. F.R. Morgenthaler, "Two-Dimensional Magnetostatic Resonances in a Thin FilmDisk Containing a Magnetic Bubble," presented at the 1978 Conference on Mag-netism and Magnetic Materials, Cleveland, Ohio, November 14-17, 1978.5. D.D. Stancil, "Magnetostatic Waves in Nonuniform Bias Fields Including ExchangeEffects," IEEE Trans. on MAG Conference Proceedings, September 1980.6. F.R. Morgenthaler, "Synthesis of Magnetostatic Waves and Modes Using Nonuni-form Bias Fields," 1980 Ultrasonics Symposium, Boston, November 1980, to bepublished in Conference Proceedings.2. OPTICAL DETECTION OF MAGNETOSTATIC RESONANCESJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)Nickolas P. Vlannes, Frederic R. MorgenthalerThe doctoral thesis of N.P. Vlannes will attempt optical detection of local-ized magnetostatic resonances in thin LPE films of YIG. At infrared frequencies,the magneto-optical response of YIG can be modeled by a dielectric tensor that isPR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)dependent upon magnetization. Thus one can probe for the characteristics of themagnetization.The experimental setup comprising a Spectra Physics 125 Laser tuned to1150 nm with lens elements for focusing the beam and optical detectors capable ofresponding to 2-GHz modulation rates is essentially complete.A list of our goals follows.1. Design and construction of an optical probing system to examine the micro-wave magnetization of magnetostatic modes of YIG;2. Design and construction of an induction probing system to sense fringingmicrowave magnetic fields;3. Use of the probing systems to probe for the respective rf fields of YIG,particularly under nonuniform bias-field conditions;4. Conduct experiments on the effects of different antenna geometries andantenna orientations relative to the YIG substrate in regard to signalprocessing character and field patterns;5. Test the microwave magnetic effects of various nonuniform bias fieldsinduced by varied-magnet pole-piece geometries.3. MODE SYNTHESISUnited States Air Force (Contract F19628-79-C-0047)Daniel Fishman, Frederic R. MorgenthalerNonuniform magnetic bias field can control magnetostatic waves and modes inferrite thin films. Gradients in either the field magnitude, direction or bothcan be employed to synthesize wave or mode spectra to prespecified characteristics.Parameters affected include frequency, rf energy distribution, impedance,velocity of energy circulation, and the threshold governing the onset of nonlineareffects due to parametrically unstable spin waves.The important case of a thin-film disk that is surrounded by free space andmagnetized to saturation along the normal to its plane was analyzea in the 1980Intermag Conference Proceedings1 for the conditions of weak-to-moderate radialgradients or arbitrary form:PR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)Hz(r) A + Z B r2nn=lThe non-"virtual-surface" modes analyzed are quasi-two-dimensional in that therf magnetization is assumed to be without appreciable thickness variation; thefringing magnetic fields are, of course, three-dimensional because the disk is sur-rounded by free space.The results allow one to synthesize modes with prespecified characteristics,such as frequency, energy distribution, velocity of energy-circulation impedancelevel, and power threshold for nonlinear behavior.If it is desired to create a spectrum with the resonance frequencies separatedby prespecified amounts or if one wishes to control the velocity of energy circu-lation V of individual modes, the independent constants B can be adjusted and thenrequired field H (r) synthesized.EControl of V not only affects the group delay of signals propagating throughthe mode but also the total energy, E, of the mode in terms of the signal powerP .The normally slow energy circulation that occurs when B = 0 can either bespeeded up or slowed down. In the latter event, the direction of net power flowcan even be reversed. Near the balance point where V = 0, E becomes very large,for a fixed value of P . Because nonlinear behavior, due to parametric spin-waveinstabilities, occurs when the energy density of the mode reaches a critical value,it follows that the threshold power of the limiting level should be gradient-controllable.It is useful to realize that VE can be forced to be independent of m over somerange of m. This also suggests that magnetostatic plane-wave propagation can bemade precisely nondispersive over a predetermined bandwidth.In Fig. XIII-2, we give the theoretical curves that result from forcing VEto be constant for the first three modes (m = 1,2,3) by means of Bl,B 2,B3.PR No. 123Z--A t* -aX (U$iTS= i- i-- -NIT'Z- -i 0 .00 1. C5i6.85 +, +8.15*6.'D J.0.4 0 *0. i *58. 5 0*8.55t,8.68 *.8.65+a.78+B.75+8.8 *e.9 , ,,8.95; *1.88;-X UNITS= 1i :Y <UNITS= E-2) +8.18 1.88 !------- -------------I-I4184iii- *12 +i4 *i5 +i6 *17 *17 *284Fig. XIII-2. The normalized mode frequency (a) and prespecified energy frequency (b) bothplotted vs mode number, together with the required field profile (c) plottedvs radius.(XIII. MICROWAVE AND QUANTUM MAGNETICS)References1. F.R. Morgenthaler, "Synthesized Magnetostatic Resonances in a NonuniformlyBiased Thin Disk without Conducting Boundaries," IEEE Trans. on MAG ConferenceProceedings, September 1980.4. NEW TECHNIQUES TO GUIDE AND CONTROL MAGNETOSTATIC WAVESUnited States Air Force (ContractJoint Services Electronics ProgramF19628-79-C-0047)(Contracts DAAG29-78-C-0020 andDAAG29-80-C-O104)Daniel D. Stancil, Frederic R. Morgenthaler, Dale A. ZeskindThe prospect of guiding magnetostatic waves is of considerable interest be-cause of possible device applications. Such guided waves might be used to increasethe delay time realizable on a given-size sample by meandering the path, or to makea resonator by guiding the waves along a closed loop. In addition, controllingthe coupling between adjacent waveguides could make possible signal-routing devicessuch as directional couplers.Guiding magnetostatic surface waves (MSSWs) is complicated by the fact thatMSSW propagation is only possible in one direction on a given surface when theapplied in-plane bias field is uniform; turns of 900 would normally require con-version to backward-volumePermalloy r,,r, htrnt waves.strips.- YIGGround p- HDCFig. XIII-3.PR No. 123xBasic experimental configuf ilm It should be possible to-Alumina overcome this difficulty byemploying gradients that arisefrom a change in the directionlane of the bias field. As an ex-ample, consider a YIG film thatis covered with permalloy con-taining a slot of controlledwidth. If the permalloy is ata different magnetostatic poten-ration. tial on either side of the slot,vvv ~uvcllr ulr,(XIII. MICROWAVE AND QUANTUM MAGNETICS)the dc magnetic field will be parallel to the film in the region underneath theslot but normal to the film surface in those portions directly underneath thepermalloy.The in-plane fields permit magnetostatic surface wave propagation; the normalfields do not.Therefore the surface-wave energy should be localized under the air-filledslot rather than under the conducting permalloy; eddy-current dissipation is there-by minimized.Notice also that if the entire field is normally directed, the surface wavedisappears completely. Taken together, these factors should allow novel controlof the surface-wave channel. Notice,too, that the width of the slot will0 strongly affect the speed of propa-g20- gation and more than one slot canLo be placed side-by-side to providecoupled-wave possibilities. The slots1 can be curved or even meandered withthe in-plane field automatically ad-^ _justing direction to maintain thesurface-wave conditions. Such curved0.35 - r __ paths can be closed themselves to01 form resonant tracks that are singleO.3 or multiple.As a first step toward evalu-0.25ating this approach, we have con-O.2I ducted preliminary experiments and2.0 2.4 2.8 3.2 have recently reported1 the observa-Frequency (GHz)tion of magnetostatic surface wavesFig. XIII-4. (MSSWs) in a rectangular YIG filmMSSW transmission spectra as a function of placed between strips of permalloythe spacing between permalloy strips. The and in the plane of the strips. Infine structure near the high-frequency end such a configuration, shown in Fig.is due to interference with the EM feed-through. XIII-3, the dc magnetic field betweenPR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)the permalloy strips is primarily in-plane with a minimum halfway between thestrips. In the presence of such a gradient, a series of discrete modes appearsbelow the low-frequency end of the continuous MSSW band as shown in Fig. XIII-4.We report here the results of pulse-time-delay measurements indicating that thesemodes travel several times faster than normal MSSW modes, in agreement with pre-vious cw measurements.Fig. XIII-5.g Surface wave precursors. (a) Precur-O 150 200 sor due to leading edge of a pulsenS centered at 2.000 GHz with H = 300 Oeand bottom of the band measured to beE 2.388 GHz. Nominal film thickness s =5 microns. (b) Theoretical precursorbased on H = 300 Oe, 4 Ms = 2122 G,Cr s = 3.19 microns, and L = 1 cm.(b)130 140 150 160 170nSWe also reported2 the experimental observation of MSSW precursors in bothuniform and nonuniform fields. An approximate theory for the precursors in a uni-form field has been developed which agrees well with the measurements. The com-parison is shown in Fig. XIII-5.PR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)References1. D.D. Stancil and F.R. Morgenthaler, "Magnetostatic Surface Modes in a Thin Filmwith Nonuniform In-Plane Fields," IEEE Trans. on Magnetics, Vol. MAG-16, No. 5,September 1980.2. D.D. Stancil and F.R. Morgenthaler, "The Effects of Nonuniform In-Plane Fieldson the Propagation Characteristics of Magnetostatic Surface Waves," 1980 Ultra-sonics Symposium, November 1980, to be published in Conference Proceedings.5. MAGNETOSTATIC WAVE-DISPERSION THEORYUnited States Air Force (Contract F19628-79-C-0047)Joint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)Frederic R. Morgenthaler, Tushar Bhattacharjee, Daniel D. StancilIn our prior analyses of nonuniform magnetostatic modes in thin films, thebias field was assumed to be directed normal to the plane and the modes consideredwere quasi-two-dimensional in that thickness variations of the rf magnetizationwere ignored. This restriction conformed to the geometry of several experimentalconfigurations but our most recent studies1 have involved films with nonuniformin-plane bias and, consequently, we have now developed a general theory, basedupon coupled-integral equations, that can deal with surfacelike modes in one ormore concentric thin-film rings when the bias and any material nonuniformities(such as variation of the saturation magnetization) are purely radial. We havealso treated the analogous integral equations based upon Cartesian coordinates forfilm configurations that involved one or more rectangular strips. Exchange effectsand thickness variations of the bias field and material parameters are not includedin the model but, because surface-wave character is expected, such variations ofthe rf fields are permitted.The boundary conditions required at the film surfaces are built directly intothese equations; the transverse conditions enter through the components of thePolder susceptibility tensor.The equations govern a very wide range of physical situations. For example,coupling between modes circulating on two concentric annular rings spaced by anair gap can be handled as can the analogous problem involving two ferrite strips.Computer algorithms for numerical solutions of this class of eigenfrequencyPR No. 123(XIII. MICROWAVE AND QUANTUM MAGNETICS)problem are currently being developed.References1. F.R. Morgenthaler, "Magnetostatic Surface Modes in Nonuniform Thin Films withIn-Plane Bias Fields," 26th Conference on Magnetism and Magnetic Material,Dallas, Texas, November 1980.6. MAGNETOELASTIC WAVES AND DEVICESUnited States Air Force (Contract F19628-79-C-0047)Joint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)Frederic R. Morgenthaler, Leslie M. ItanoA microwave yttrium-iron-garnet (YIG) delay line can be made to provide lin-early dispersive delay with instantaneous bandwidth in excess of 1 GHz in C-band.The dispersion of the device is based on the properties of spin and elastic wavesin magnetically biased YIG, a ferrimagnetic material. In particular, linear dis-persion can be achieved by first specifying a particular dc magnetic-field profilealong the axis of a YIG rod, and then designing the necessary pole pieces withthe aid of a computer.The first generation of thin-film antennae were fabricated, but the resultswere disappointing. A second set of designs is currently being processed, andmodifications of the test fixture are being made that are expected to increasethe focusing of the magnetostatic backward wave into the magnetoelastic beam. Thehoped-for result will be an increase in coupling efficiency and consequent reduc-tion in the insertion loss of the magnetoelastic wave signal.PR No. 123

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