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The high power ferromagnetic resonance (FMR) response, as well as butterfly curves of the spin wave instability threshold microwave field amplitude hcrit versus in-plane static field H profiles, have been measured for Permalloy films with thicknesses of 104, 128, and 270nm at a nominal pumping frequency of 9.37GHz. The hcrit values range from about 1 to 7Oe. Both the resonance saturation response at the FMR field and the subsidiary absorption (SA) response for static fields below the FMR field are similar in appearance to those for bulk ferrites. Butterfly curves over the SA response region, while similar to those for ferrites, exhibit a film thickness dependent band edge cutoff effect not found in bulk ferrites. The SA butterfly curve data were analyzed on the basis of a spin wave instability theory adapted to thin films. The observed shift in the SA band edge cutoff with thickness agrees with calculations based on the thin film dispersion response and the assumption of first order instability processes ...

The nonlinear decay of continuous-wave magnetostatic surface wave and backward volume wave signals has been measured for propagation in a narrow 6.9 μm thick yttrium–iron–garnet film strip, with excitation frequencies and wave numbers between 5470 and 5630 MHz and 47 and 216 rad/cm, respectively. The results show: (1) that the onset of nonlinear damping is a threshold effect, and (2) that a nonlinear decay model with two damping terms, one linear and one quadratic in the wave power, are needed to model the measured response.

The ferromagnetic resonance (FMR) linewidth, the field dependent effective linewidth, and the parallel pump spin wave linewidth were measured for spheres and disks prepared from a block of hot isostatic pressed (hipped) polycrystalline yttrium iron garnet (YIG). All linewidths as well as static magnetization data indicate close to 100% density. Vibrating sample magnetometer measurements give an average saturation induction 4πMs of 1825 G. The FMR half-power linewidths for the spheres at 9.5 GHz were 13 Oe. Linewidths measured over the 9.5–18 GHz frequency range show a small but distinct drop and agree with Schlomann’s theory of anisotropy-dominated two-magnon scattering for polycrystalline ferrites. The effective linewidth versus field data at 10 GHz show a region of strong absorption that corresponds to the width of the spin wave manifold for low wave numbers and a high field value of about 2 Oe. Parallel pumping measurements give minimum spin wave linewidths of 1.2 and 0.6 Oe at 9 and 16.7 GHz, respecti...

Spatial recurrence for nonlinear magnetic excitations has been observed. The recurrence was produced from the induced modulational instability of two input magnetostatic backward volume waves in a thin yttrium iron garnet film. The nominal frequency, frequency separation, and wave number were 5.5 GHz, 8 MHz, and 100 rad/cm, respectively. The spatial recurrence of the temporal wave form included frequency doubling and cnoidal profiles. A superposition of modes based on the observed Fourier makeup of the signals and calculated nonlinear phase shifts gave a response which matched the data.

The oblique pumping spin wave instability threshold microwave field amplitude hcrit was measured as a function of the static field for both in-plane and out-of-plane static fields for a thin disk of Mn substituted Zn–Y (Ba2Zn2Fe12O22) easy plane hexagonal ferrite at 16.7 GHz. Theoretical fits to the in-plane static field data gave a single value of 12.8 Oe for the spin wave linewidth ΔHk. The best overall fits were for a critical spin wave mode wave number k close to zero and there was no correlation with the critical mode propagation directions. The fitted ΔHk for the out-of-plane static field geometry was found to increase with the out-of-plane magnetization angle, but showed no correlation with the critical mode propagation directions. These critical modes had k≈0 as well. The fitted ΔHk increased from the in-plane field value of 12.8 Oe to a value of 21 Oe at the maximum accessible magnetization angle of 70° relative to the disk plane. This increase in spin wave damping with the out-of-plane angle is ...

An analysis of nonlinear magnetostatic surface wave pulse propagation in planar ferrite-dielectric-metal (FDM) structures has been performed. The analysis was based on numerical solutions to the higher-order nonlinear Schrodinger (HONLS) equation, with third-order (D3) and nonlinear (Q) dispersion terms taken into account. The analysis focuses on (1) the crossover dispersion region for FDM structures and the point in wave-number k where the second-order dispersion parameter D2 is a positive maximum, the Lighthill criterion for envelope soliton propagation is satisfied, and D3 is close to zero, and (2) the end points of this crossover region where D2 is zero. All operational HONLS equation parameters were evaluated from analytical dispersion expressions for the FDM structure and for magnetic field and structure parameters which match experiments. For (1), the pulse results indicate nondispersive propagation consistent with envelope solitons. The only effect of the Q term is to decrease slightly the propaga...

The parallel pump spin wave instability threshold field hcrit was measured as a function of static field for various size in-plane magnetized thin plates of single crystal Mn substituted Zn-Y at both 9 and 16.7 GHz. The 9 GHz data indicate that (1) the critical modes consist of standing magnetostatic waves and (2) the hcrit thresholds depend on the lateral dimensions of the sample. The minimum parallel pumping spin wave linewidths were in the range 3–10 Oe and increased with a decrease in the sample lateral dimensions. These data are consistent with a transit time model and a size limited spin wave linewidth for low wave number critical modes. At 16.7 GHz, thresholds and spin wave linewidths are consistent with the 17.5 GHz and 9.5 GHz ferromagnetic resonance linewidth results and are sample size independent. The data indicate that exchange dominated spin waves are excited for fields below the butterfly curve minimum. These data give a k-dependent spin wave linewidth. The minimum parallel pumping spin wav...

The half power ferromagnetic resonance (FMR) linewidth ΔH has been measured from 8 to 300 K for a nominal frequency of 61 GHz and from 50 to 75 GHz at room temperature for normally magnetized single crystal platelets and pulsed laser deposited (PLD) films of barium ferrite. The platelet linewidth versus temperature data show a peak value of 27 Oe at 25–30 K, a dip to 21 Oe at 75 K, structure related to line merging at 130–160 K, and a region of slow increase at 240–295 K. The 240 –300 K data extrapolate to a 0 K linewidth of about 8 Oe. The corresponding film data show a peak value of 240 Oe at 20 K and a gradual decrease at higher temperatures. Both the platelet and film linewidths show a weak frequency dependence at about 0.3 Oe/GHz at room temperature (RT). The film data also show several linewidth spikes due to interference effects between the FMR response and dielectric resonances in the substrate. The RT linewidth zero frequency intercepts for the platelet and the film were 9 and 30 Oe, respectively...

Resonance saturation (RS), subsidiary absorption (SA), and parallel pump (PP) spin wave instability threshold measurements have been made on single crystal easy plane disks of Mn substituted Zn–Y type hexagonal ferrite materials at 8.93 GHz and room temperature. For each configuration, “butterfly curves” of the spin wave instability threshold microwave field amplitude hcrit as a function of the static field applied in the disk plane were obtained. The previous theory for these instability processes was also extended to include planar magnetocrystalline anisotropy and a wave vector k dependent spin wave linewidth, ΔHk. The RS butterfly curve had a characteristic “V” shape with a rounded minimum at the ferromagnetic resonance (FMR) field. The nominal ΔHk needed to fit the data at the ferromagnetic resonance field was 7 Oe, but the butterfly curve shape indicated a k-dependent ΔHk. The butterfly curves for the PP configuration were flat at low field and then diverged rapidly at the cutoff field for first ord...

Recently obtained single soliton solutions to the nonlinear Schrodinger equation with additional higher order nonlinear and dispersion terms have been used to model the properties of microwave magnetic envelope solitons in thin films and, in particular, the recently observed power-dependent soliton velocity in these films. The modeling is based on an empirical scaling between the dimensionless amplitude parameters in the higher order nonlinear Schrodinger (HONLS) equation and the pulse power levels in the experiment. Based on this scaling, the amplitude-dependent soliton velocity from the HONLS equation solution is shown to match the velocity versus power response from the experiment.

Shorted waveguide ferromagnetic resonance (FMR) measurements were made at 9.5 GHz for pulsed laser deposited yttrium iron garnet (YIG), MnZn ferrite, and NiZn ferrite films with thicknesses of 1.8, 0.5, and 1.5 μm, respectively. The FMR field versus the field angle confirmed the operational assumption of a uniform mode response. For the YIG, the linewidth was 10 Oe when the external field and magnetization vectors were perpendicular to the disk (perpendicular FMR) and increased smoothly to a maximum value of 27 Oe when the field and magnetization were in the film plane (parallel FMR). For the MnZn, the linewidth was 49 Oe at perpendicular FMR, increased with the angle between the film normal and the external field to a broad maximum of 80 Oe at 35°, and then dropped to 65 Oe at parallel FMR. For the NiZn, the linewidth was 310 Oe at perpendicular FMR, increased with the field angle to a broad maximum of 1530 Oe at 45°, and then dropped to 960 Oe at parallel FMR. The linewidths were larger than predicted f...

A theoretical analysis of microwave magnetic envelope soliton profiles and the soliton peak power response for high power magnetostatic wave (MSW) excitations in yttrium iron garnet (YIG) thin films has been made. This analysis was based on the standard nonlinear Schrodinger equation with all key parameters based on experiment. The measurements were done for magnetostatic backward volume waves in a 10.2 μm YIG film, with a band edge at 5.06–5.07 GHz and operating point frequencies from 4.80 to 5.00 GHz. The use of accurate dispersion and group velocity parameters and the transmitted power versus frequency response of the MSW signal was critical. It was possible to accurately model both the shapes of the soliton pulses and the peak output versus peak input power response over a wide range of power levels.

A detailed analysis of the two magnon scattering contribution to the microwave relaxation and ferromagnetic resonance linewidth in isotropic and anisotropic films and disks has been made. The analysis is based on the Sparks, Loudon, and Kittel (SLK) theory for the scattering of uniform mode magnons into degenerate spin wave states for isotropic spherical samples in the presence of magnetic inhomogeneities in the form of spherical voids or pores. The SLK theory has been extended to include: (i) thin film and thick film samples magnetized in an oblique out-of-plane direction; (ii) uniaxially anisotropic materials with either easy-axis or easy-plane anisotropy and an anisotropy axis perpendicular to the disk plane; (iii) a modified density of degenerate states to account for the nonzero relaxation rate of the scattered spin waves; and (iv) two limiting cases of the scattering interaction: (a) the original SLK case where the inhomogeneities are modeled as spherical voids and the coupling to the degenerate spi...

A new method for the analysis of microwave magnetic envelope (MME) solitons has been developed. This method is based on the determination and analysis of output microwave pulse phase profiles. Simple analytical results based on the nonlinear Schrodinger equation show that MME soliton phase profiles contain the necessary and sufficient information needed to define a particular pulse as a linear dispersive pulse or a fully formed soliton. The effects are demonstrated both theoretically and experimentally for magnetostatic backward volume wave and magnetostatic surface wave pulse signals. Theoretical phase profiles are considered for Gaussian, hyperbolic secant, and rectangular pulse shapes. Experimental profiles are obtained for rectangular input pulses. The measured phase profiles compare favorably with the numerical results. Both the data and the theory show that a constant phase profile across the pulse provides a consistent and quantitative criterion for an MME soliton.

Ferromagnetic resonance measurements were made as a function of the static external field angle for c-plane disks of single crystal flux grown manganese substituted barium M-type (Ba-M) and zinc Y-type (Zn-Y) hexagonal ferrites at 50 and 8.8 GHz, respectively. A shorted waveguide technique was used. Analysis of the FMR field versus angle results confirmed the operational assumption of a uniform mode response. For the easy-axis Ba-M disk, the linewidth was 69 Oe when the external field and magnetization vectors were perpendicular to the disk. The linewidth increased to a maximum measured value of 472 Oe when the magnetization was directed 45.4° from the sample normal. For the easy-plane Zn-Y disk, the linewidth had a minimum value of 18 Oe when the field and magnetization vectors were in-plane. The maximum linewidth was 391 Oe when the magnetization was directed 25.2° from the disk normal. The linewidths were larger than predicted for reasonable values of the Landau–Lifshitz damping and showed angle depend...

Combined Brillouin light‐scattering (BLS) and microwave pumping techniques were used to measure the second‐order spin‐wave instability threshold microwave field amplitudes and characterize the critical modes for ferromagnetic resonance (FMR) saturation in 4.15 μm‐thick yttrium iron garnet films at 8.47 GHz with the static magnetic field in‐plane. To the best of our knowledge, this work represents the first BLS measurements for second‐order FMR saturation processes in ferrite materials. Several new results were obtained: (1) A new type of butterfly curve for second‐order processes. (2) Strong scattering from modes at low wave numbers in the 104 rad/cm range. (3) An observed in‐plane propagation direction for these low wave number modes at 90° to the in‐plane static field direction. These results differ significantly from the behavior expected from the bulk sample instability theories of Suhl and Schlomann, which predict critical modes at wave numbers and propagation directions in the 105–106 rad/cm and 0° ...

The dynamic microwave magnetization (DMM) amplitude of magnetostatic waves in yttrium iron garnet films at 5–6 GHz has been measured as a function of input power. The measurement is based on the characteristic frequency shift in the power transmission spectrum. This shift is related to the reduction of the effective static magnetization and, therefore, the increase of the DMM amplitude at high power. The measurements were made on 7.2‐μm‐thick, single‐crystal yttrium iron garnet films. A pulsed frequency‐swept microwave signal at 5–6 GHz was used to launch the magnetostatic waves. The signals were excited and detected by planar microstrip transducers. Measurements were made for magnetostatic forward volume waves (MSFVW) and magnetostatic surface waves (MSSW). The duty cycle of the pulsed microwave signal was kept at 0.1% in order to avoid sample heating effects. The shifts for small features in the transmission vs frequency profiles were used to determine the DMM amplitudes. At low power, the DMM amplitude...

We use nuclear magnetic resonance spectroscopy of alkali metals sealed in glass vapor cells to perform in situ identification of chemical contaminants. The alkali Knight shift varies with the concentration of the impurity, which in turn varies with temperature as the alloy composition changes along the liquidus curve. Intentional addition of a known impurity validates this approach and reveals that sodium is often an intrinsic contaminant in cells filled with distilled, high-purity rubidium or cesium. Measurements of the Knight shift of the binary Rb–Na alloy confirm prior measurements of the shift's linear dependence on Na concentration, but similar measurements for the Cs–Na system demonstrate an unexpected nonlinear dependence of the Knight shift on the molar ratio. This non-destructive approach allows monitoring and quantification of ongoing chemical processes within the kind of vapor cells which form the basis for precise sensors and atomic frequency standards.

The ac electrical behavior of the polycrystalline yttria was evaluated in the temperature range of 800–1300 °C in air as a function of frequency (5 Hz≤f≤13 MHz). Resistance‐temperature and resistance‐time (aging) characteristics were examined using immittance measurements and electron microscopy to establish microstructure‐property relationships. The ac electrical data indicated two distinct relaxations when analyzed in the impedance plane. These relaxations are attributed to the lumped grain and grain‐boundary contributions in conjunction with a polarization effect at the electrode/sample interface. The admittance plane analysis revealed a semicircular relaxation in the low‐frequency region, indicative of a trapping effect associated with grain‐boundaries and the electrode/sample interface. The variation in the total electrical resistance with time is found to be dependent on the starting microstructure of the sample. A sample with a larger grain size shows a smaller degree of aging at elevated temperatures. Immittance measurements suggest that the major contribution to the aging behavior comes from the evolution in the microstructure.

Magnetostatic forward volume wave (FVW) microwave magnetic envelope solitons in 7.2 μm thick, single‐crystal yttrium iron garnet films have been studied at 5.6–6.0 GHz. Rectangular input pulses with peak powers up to 3 W and pulse widths 5–50 ns were used. Single soliton output pulses with a characteristic increase in amplitude and pulse narrowing are observed when the power or width of the rectangular input microwave pulse exceeds threshold levels. Above these levels, output pulse peak power versus input power or pulse width exhibits a nonlinear increase and shows saturation effects. Multiple peak output profiles are observed for pulse powers and widths well above threshold. Solitons could be formed for all frequencies within the usable, low transmission loss portion of the magnetostatic FVW band. The use of reflected pulses from the film edge made it possible to study soliton decay and soliton collisions. The soliton decay rate was found to be approximately twice the linear rate, as expected from theory...

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...

Brillouin light scattering (BLS) in the backscattering configuration has been used to study the magnetic excitations in epitaxial Fe(38 A)/Cr(13 A)/Fe(38 A) thin‐film sandwiches. Spin‐wave frequency was measured versus in‐plane wave vector k and static in‐plane magnetic field H for both [100] and [110] direction fields and with k perpendicular to H. The range of applied fields was 50–1500 Oe. The wave‐number range was 0.45×105–2.3×105 rad/cm. The BLS spectra correlate with magnetization versus field profiles and confirm the antiferromagnetic coupling between the Fe layers. Under low‐field conditions and near‐antiparallel alignment of the Fe layer magnetization vectors, the spin‐wave frequencies from the Stokes and anti‐Stokes sides of the BLS spectra are different. These frequencies merge at high field. The low‐field splitting feature is very sensitive to small differences in thickness for the magnetic layers and indicates a thickness difference of 9%. Matchups between features of the BLS data and magneti...

A fine structure in the parallel pumping spin wave instability absorption has been observed. The data were obtained at 9.4 GHz on a narrow linewidth in‐plane magnetized yttrium iron garnet film with a magnetic layer thickness of 15.9 μm. The standard butterfly curve of the spin wave instability threshold microwave field amplitude hcrit versus external static magnetic field Hext was constructed from hcrit determinations obtained by sweeping the static field at different microwave power levels and measuring the change in microwave loss. For values of Hext below the minimum, hcrit position, the loss versus Hext profiles showed a characteristic fine structure previously observed only in spheres. The fine structure spacing was on the order of 5 Oe and the square of the spacing decreased linearly with increasing static field. These fine structure results are in accord with predictions from theory for critical modes at one‐half the pump frequency, with the critical mode wave vectors aligned perpendicular to the ...

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...

Butterfly curves of the subsidiary absorption spin wave instability threshold microwave field amplitude versus static field have been measured at 10 GHz on a 12.8‐μm‐thick single crystal yttrium iron garnet film for two field configurations, one with the static magnetic field in plane and the microwave field out of plane (IP case) and the other with the static field normal to the film plane and the microwave field in plane (PI case). The results for the IP case are similar to earlier results which show a ‘‘kink’’ in the butterfly curve accompanied by a jump of the critical mode wave number k at the kink field. For the PI case, however, there is no observed kink effect. The different butterfly curves for the IP and PI cases are explained on the basis of a new theory for thin films which takes into account the discrete standing wave modes in the film. For the IP case, the theory yields critical modes with wave vectors in the film plane and the kink effect as before. For the PI case, the critical modes have ...

Ferromagnetic resonance (FMR) and high field effective (HFE) linewidth measurements have been made at 10–90 GHz for low conductivity Mn substituted single crystal barium ferrite, BaFe12−xMnxO19, with x=0.1. The manganese compensates excess Fe2+ and reduces conductivity. Measurements were made on c‐plane thin disks magnetized to saturation along the disk axis. A shorted waveguide technique was used to measure the FMR profiles and linewidths in the 55–90 GHz frequency range. High Q cavity techniques and an analysis procedure for the FMR high field tail response were used for the HFE linewidth determinations in the 10–60 GHz frequency range. The FMR linewidths increase linearly with frequency at 0.3 Oe/GHz and have a zero frequency intercept of 20 Oe. The HFE linewidths increase linearly with frequency at 0.4 Oe/GHz and have a zero frequency extrapolation of 4 Oe. This lower zero frequency extrapolation for the HFE linewidth supports an inhomogeneity origin for the 20 Oe FMR linewidth extrapolation. These da...

Dipole‐exchange spin wave pulses in magnetic thin films have been numerically modeled with the nonlinear Schrodinger equation. Small input pulse amplitudes yield propagating wave packets which exhibit a linear response. As the amplitude of the input pulse is increased, the propagating spin‐wave pulse exhibits soliton and then multisoliton structures. In the soliton regime, three principal characteristics are observed. First, in the zero damping limit, the soliton propagates without changing its shape. Second, the soliton exhibits an inherent velocity in addition to its linear group velocity. Third, the soliton exhibits a damping rate that is approximately twice that in the linear regime.

We have studied the time response of visible, red photoluminescence in anodically etched p− silicon films. The principal features of our measurements are luminescence with two wavelength components, and a temperature dependent rise time of 24 μs and a decay time of 47 μs at room temperature. Results from our samples show some similarities to characteristics measured in amorphous Si, suggesting that some low‐dimensional or disordered Si phase may play a role in the observation of visible light from this new photonic material.

Subsidiary absorption butterfly curves of spin‐wave instability threshold versus static in‐plane field have been obtained for yttrium iron garnet (YIG) thin films at 3 GHz. The butterfly curves have been found to be rather anomalous, typically displaying a pronounced dip and a very low minimum threshold. These anomalous features are attributed to the overlap of the subsidiary absorption field region with ferromagnetic resonance (FMR). First‐order instability theory was extended to include the uniform mode response near FMR. The extended theory yields good fits to the data for reasonable values of the YIG FMR linewidths. The theoretical analysis also shows a predicted flip in the azimuthal propagation angle φk for the unstable spin waves in the region of FMR overlap. With increasing field, there are predicted discontinuous changes in φk from 90° to 0° and back to 90° in the region of FMR.

Highly textured Li-ferrite films have been synthesized by pulsed laser deposition from bulk targets onto c-plane sapphire substrates. For substrate temperatures approaching 1000 °C the growth mode was predominantly (333). A similar growth mode was recently reported for Ni-ferrite films grown onto c-plane sapphire substrates. The films were 4–8 μm thick and were grown at deposition rates of 3–5 A/s at oxygen partial pressures of 200–400 mTorr. Magnetic measurements were made by SQUID and 9.5 GHz ferromagnetic resonance (FMR) on the as deposited films. Textured Li-ferrite films with x-ray diffractometer intensity ratios of I(333)/I(311)=10.3 for films made in 200 mTorr oxygen and 14.5 for films made in 400 mTorr oxygen exhibited room temperature in-plane intrinsic coercivities of

The objective of this study was to identify any differences in the friction and wear characteristics of particulate tapes produced with various magnetic particles and metal‐evaporated (ME) tapes. Accelerated friction and wear experiments were conducted with a tape reciprocated in a shoeshine mode over an aluminum drum. We have found that barium ferrite and Co‐γFe2O3 tapes exhibit the least damage to themselves and the mating drum. The ME tape exhibited the least durability among all tapes. The effect of tape roughness on friction was found to be dependent on the hardness of the mating material. Friction increased with an increase in the roughness during the tests with a soft aluminum drum due to severe plowing of the aluminum. However, friction decreased with an increase in the roughness with a hard ferrite surface which is consistent with the asperity contacts being elastic in nature (with no appreciable plowing contribution to the friction).

A first‐order instability theory for magnetostatic modes in ferromagnetic spheres has been developed. The analysis is based on the interaction of three modes: the uniform mode pumped at microwave frequency ωp and a pair of magnetostatic modes at lower frequencies which sum to ωp. The magnetostatic mode instability arises when the pump microwave field amplitude exceeds some threshold. The theory yields (i) selection rules for the magnetostatic mode pairs with a nonzero coupling to the uniform mode, (ii) a characteristic equation for the frequencies of these modes, and (iii) microwave field threshold amplitudes for the parametric excitation of the mode pairs. For each mode pair, one or more sharp threshold minima are found. The superposition of these sharp minima resembles the complicated structure observed in the subsidiary absorption butterfly curve for single‐crystal yttrium‐iron‐garnet spheres.

A Brillouin light‐scattering study of surface magnons in permalloy thin films shows a distinct oscillation in the Stokes–anti‐Stokes intensity ratio as a function of the in‐plane wave number in the 0– 2.5×105 cm−1 range. This result differs from the previously reported monotonic dependence for thin iron thin 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.

Dielectric properties of annealed and as-grown ferroelectric Ba0.5Sr0.5TiO3 (BST) grown by pulsed laser deposition on sputtered BST seed layers on strontium titanate (STO) substrates were investigated at microwave frequencies in the realm of tunability of its dielectric constant as well as phase shifters based on this material. The as-grown layers were nearly fully relaxed with measured lattice parameters nearly identical to those of bulk BST. The tuning of the relative dielectric constant (∼1750 at zero bias at 10 GHz) of the annealed BST was found to be as high as 59% and 56% at 10 and 19 GHz, respectively. The analysis of the loss in the BST results in a measured tan δ of 0.02 for the annealed as well as the unannealed films at a frequency of 18 GHz. Phase shifters also exhibited high tuning with differential phase shift figures of merit of 35 and 55°/dB at a field of 60 kV/cm at 10 and 19 GHz, respectively. Serendipitously, most of the tuning occurs at low fields, and thus we propose a new figure of m...

Mechanical and electrical properties of carbon fiber (CF) and vertically aligned carbon nanotubes (CNTs) have been thoroughly investigated in previous studies. Growth of radially aligned CNTs on silicon oxide (SiO2) coated CF has recently been accomplished resulting in multiscale composite fiber (CNT/SiO2/CF). CNT/SiO2/CF offers promise as stress and strain sensors in CF reinforced composite materials. However, to date there have been no investigations of the electromechanical properties of CNT/SiO2/CF that would facilitate their usage as sensors in composite materials, which is the focus of this research. This study investigates fundamental mechanical and electrical properties of CF, SiO2/CF (SiO2 coated CF), and CNT/SiO2/CF during localized transverse compression at low loads (μN to mN) and small displacements (nm to a few μms). Force, strain, stiffness, and electrical resistance were monitored simultaneously during compression experiments. For CF, resistance decreased sharply upon compressive loading w...

Heusler alloy Co2MnSn1−xSbx (x=0.0, 0.5, and 1.0) thin films were grown on GaAs (001) substrates using pulsed laser deposition techniques. Growth parameters have been determined that result in highly magnetically anisotropic, crystalline, and oriented (001) films. The angular dependences, relative to the GaAs (001) crystallographic directions, of the coercive field Hc(θ) and the remanence Mr(θ) were determined from angle dependent magneto-optic Kerr effect (MOKE) measurements. It was found that Hc(θ) revealed higher order symmetry contributions to the magnetic anisotropy than did Mr(θ). The Fourier analysis of rotational MOKE data was used to determine the symmetry contributions to the total anisotropy.

We present the magnetic, structural, and transport properties of the quaternary Heusler alloys Co2MnSnxSb1−x (x=0, 0.25, 0.50, 0.75, and 1.0), which have been theoretically predicted to be half-metallic. Magnetization measurements as a function of applied field show that the saturation moment for x=1 (Co2MnSn) is near the Slater–Pauling value of 5μB; however, the moment for x=0 (Co2MnSb) falls far short of its predicted value of 6μB. Resistivity as a function of temperature was measured from 5 to 400 K, and a phase transition from a half-metallic ferromagnetic phase to a normal ferromagnetic phase was observed between 50 and 80 K for all of the alloys. At low temperature (10 K

Contact failures in microelectromechanical systems (MEMS) switches prevent widespread use of MEMS technology for current handling in miniature devices. A self-assembled monolayer (SAM) lubricant was applied to MEMS switch surfaces in this paper as a possible approach for preventing contact failure. Chemical and physical processes on SAM lubricated contact surfaces were investigated at low (10 μA) and high (1 mA) current using a micro/nanoadhesion apparatus as a switch simulator with in situ monitoring of contact resistance and adhesion force. This was coupled with ex situ analytical analyses of the contacts using x-ray photoelectron spectroscopy (XPS) and micro-Raman techniques. Diphenyl disulfide was chosen as a lubricant due to its thermal stability, enhanced conductivity, and its ability to form a 3.4 A thick SAM on the gold electrode surface. Hot switching experiments were conducted in humid air (45% RH) and dry nitrogen using a MEMS-scale contact force of 200 μN and 5 Hz frequency. At low current, lu...

A two magnon scattering theory for microwave relaxation in magnetic systems is formulated in the framework of the Hamiltonian formalism. The paper provides general expressions for inhomogeneity coupling coefficients in the case of localized inhomogeneities. An approximate solution for the relaxation rate of the ferromagnetic resonance uniform mode relaxation rate is presented. Two examples of the application of the theory are presented, one for bulk polycrystalline ferrites and one for polycrystalline metallic thin films.

High precision measurements on the low and high field effective linewidth ΔHeff at 10GHz have been made on ultradense (UD) and conventionally sintered (CS) polycrystalline yttrium iron garnet (YIG) materials. The high field data confirm previous results on the role of two magnon scattering to low wave number (k) electromagnetic Larmor branch spin waves that lie below the light line. The low field data reveal two important contributions to the effective linewidth. For a field regime from the low k edge of the usual dipole exchange spin wave band down to the point in field (H=HX) where above-the-light-line electromagnetic branch Larmor (EML-HI) spin waves appear, ΔHeff is connected with scattering to relatively high k dipole exchange Larmor (DEL) spin waves. The coupling to these modes comes from grain boundaries in the YIG materials. A grain boundary scattering theory gives reasonable agreement with the data. While the high field effective linewidth due to pseudo in-manifold scattering is larger for the CS...

A series of sintered composite materials was fabricated from Parascan™ barium strontium titanate (BSTO) and Trans-Tech nickel zinc ferrite powders. The ferrite loading was varied from zero (BSTO only) to 100wt% (ferrite only). X-ray diffraction data show the presence of a third, nonmagnetic phase that sets the ferrite loading at values somewhat lower than the as prepared wt % amounts. The average magnetization is found to scale linearly with the loading. The initial susceptibility, saturation field, and coercive force as obtained from hysteresis loop data show trends consistent with these data. Ferromagnetic resonance linewidth and effective linewidth measurements at 10GHz show reasonable values for the 100wt% samples, but any amount of BSTO causes a severe degradation in both loss parameters. Similarly, it is found that any amount of ferrite causes a rapid drop in the relative dielectric constant that is consistent with standard mixing models. Loss tangent measurements gave modest values in the 0.001–0.0...

Microelectromechanical systems (MEMS) radio frequency switches hold great promise in a myriad of commercial, aerospace, and military applications. In particular, capacitive-type switches with metal-to-dielectric contacts (typically gold-on-silicon nitride) are suitable for high frequency (⩾10GHz) applications. However, the devices are known to be unstable in their performance due to parasitic dielectric charging. Although several authors have previously reported the switch failure along with shifts in pull-down and release voltages due to charging, there is some disagreement and lack of understanding among the various reports. This study uses a switch simulator capable of measuring microscale electrostatic and adhesive forces to investigate charging and its effect on reliability and fundamental forces acting within MEMS capacitive switches. An important advantage of the switch simulator is that it can be actuated with or without a bias voltage. Electrostatic force and dielectric charging increased as surf...

Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

Fast pulse-driven spin-wave excitations in magnetic films have been studied experimentally and theoretically. The experiment was conducted on a low loss yttrium iron garnet thin-film strip with separate microstrip lines for excitation and detection. The theoretical analysis was based on the full spatio-temporal Fourier response of the input pulse/microstrip line configuration and the spin-wave dispersion for the film. The data and analysis provide a clear and precise picture of the manner in which the fast pulse-excited spin-wave signals are defined and controlled by the interplay of pulse rise time, excitation geometry, and spin-wave dispersion. The amplitude of the spin-wave wave packet associated with the leading or trailing edges of the drive decreases with the pulse rise time and the static magnetic field, and increases with the pulse amplitude. The spectral profile of the spin-wave excitation is highly asymmetric, with a steep lower-frequency edge and a gradual upper-frequency edge. The spectral ban...

Lithium zinc ferrite (LiZnF) films were prepared for a wide range of deposition parameters. Bulk LiZnF rather than pure Li ferrite targets were used to mediate the mismatch problem between the film and the MgO substrate. Preparation conditions were optimized to give single phase epitaxial films with half power ferromagnetic-resonance (FMR) linewidths of as low as 57 Oe at 9.5 GHz. The films were deposited on (100)-plane MgO substrates with a KrF excimer laser at a wavelength of 248 nm. The minimum linewidth films with a thickness of 0.70 μm were obtained for an oxygen partial pressure of 400 mTorr, a substrate temperature of 800 °C, and a laser fluence of 1.7J∕cm2. X-ray diffraction pattern indicated a pure LiZn phase with local normal axis deviations below 0.05°. The FMR profiles were measured at 9.5 GHz with the static field perpendicular and parallel to the film plane, and as a function of rotation angle for in-plane fields. The data yielded a saturation induction 4πMs value of 2.730 kG, about the same...

High-precision high-field effective (HFE) linewidth measurements have been made at 10GHz on ultradense hot isostatic pressed and conventionally sintered (CS) yttrium iron garnet ferrite materials. The accuracy was increased ten-fold relative to previous data through the use of a high-quality cavity, a modified measurement technique, and a fine adjustment of the gyromagnetic ratio based on the field-frequency response of the loaded cavity. The HFE linewidths for fields well above the region of degenerate bulk spin-wave band decreases with increasing field and extrapolates to known intrinsic single-crystal linewidths in the extreme high-field limit. From a field point shifted up from the high-field band edge dependent on degenerate dipole-exchange spin waves by 2∕3 the saturation induction, the data track closely the computed density of states for electromagnetic spin waves. In the case of the CS material, for fields below this point, one sees a microstructure-related increase related to conventional modera...

Hexagonal M-type barium ferrite (BaM) films have been prepared by pulsed laser deposition. Optimal preparation conditions gave pure single phase films with the narrowest possible ferromagnetic resonance (FMR) linewidths. The films were deposited on c-plane sapphire substrates with a KrF excimer laser at wavelength of 248 nm and fluence of 1.7 J/cm2. The minimum linewidth films were obtained for an oxygen partial pressure of 300 mTorr and a substrate temperature of 910 °C, and were 0.85 μm thick. X-ray diffraction indicated pure single crystal BaM phase with local c-axis deviations less than 0.15°. Vibrating sample magnetometry data gave hysteresis loops with minimal hysteresis and small coercive force, saturation induction 4πMs of 4.2 kG and uniaxial anisotropy field HA of 16.4 kOe. The HA matches the anisotropy for bulk and the 4πMs is about 10% below literature values for the bulk. The FMR spectra were measured from 50 to 75 GHz by shorted wave guide techniques with the static field perpendicular to the...

Solitons are nonlinear propagating wave pulses that preserve their shape without spreading. Recently, microwave envelope solitons have been observed in thin yttrium iron garnet (YIG) films for magnetostatic surface wave and forward volume wave configurations. In this work, we report the first observation of microwave envelope of magnetostatic backward volume waves (MSBVW) for an in‐plane magnetized YIG film with waves propagating parallel to the magnetization direction. Both soliton profiles and the nonlinear peak power response were observed. The experiments were conducted using a microstrip magnetostatic wave delay line structure. A single crystal YIG film of 7.2 μm thickness, 2 mm×15 mm in size, and with unpinned surface spins was magnetized in‐plane by a static external field of 1343 Oe along the long 15 mm edge. The 10 GHz ferromagnetic resonance linewidth of the film was 0.6 Oe. Square microwave pulses with pulse widths from 2 to 200 ns and a carrier frequency of 5.78 GHz were launched parallel to t...