Microstrip Transducer Research Articles

Зависимость спектра спин-волновых возбуждений магнонного кристалла от поля подмагничивания

The spectrum of spin waves (SW) of tangentially magnetized films of yttrium iron garnet (YIG) with a surface metastructure in the form of gratings of etched grooves with a period Λ close to the film thickness d (Λ~d) has been experimentally and numerically studied. It has been found that the spectrum of the signal reflected from a microstrip transducer with a width w>>d,Λ located on the YIG film contains absorption lines associated with the excitation of the SW of the surface metastructure. In the case when the magnetic field H and the transducer are oriented along the grooves, the absorption lines of the metastructure are located at frequencies f* near the short-wavelength edge of the spectrum of the surface magnetostatic (Damon-Eshbach) wave fs. It is shown that f* linearly depends on H , which can be used to develop magnetic field sensors. The results of measurements of dependences f* (H) are in qualitative agreement with the results of micromagnetic modeling.

Magnetic sensor based on spin waves

The spectrum of spin waves (SW) of tangentially magnetized films of yttrium iron garnet (YIG) with a surface metastructure in the form of gratings of etched grooves with a period close to the film thickness d (~ d) has been experimentally and numerically studied. It has been found that the spectrum of the signal reflected from a microstrip transducer with a width w>> d, located on the YIG film contains absorption lines associated with the excitation of the SW of the surface metastructure. In the case when the magnetic field H and the transducer are oriented along the grooves, the absorption lines of the metastructure are located at frequencies f* near the short-wavelength edge of the spectrum of the surface magnetostatic (Damon--Eshbach) wave fs. It is shown that f* linearly depends on H, which can be used to develop magnetic field sensors. The results of measurements of dependences f*(H) are in qualitative agreement with the results of micromagnetic modeling. Keywords: magnetostatic waves, one-dimensional grating, surface structure, sensor of magnetic field.

A weak-field magnetometer based on a resonator microstrip transducer with thin magnetic films

A high-sensitivity magnetometer of weak quasi-stationary magnetic fields is developed and investigated. The magnetometer transducer is a microstrip resonator with an active medium from thin magnetic films prepared by magnetron sputtering of a Ni75Fe25 permalloy target. It is demonstrated that the transducer exhibits the maximum sensitivity not only in the optimal dc magnetic field, but also at the optimal deviation of this field from the rf pump field polarization direction. The magnetometer operates in a wide dynamic range of measured magnetic fields from 10−4 to 10−2 μT at frequencies of 10−1–105 Hz.

Nonreciprocal Tunable Low-Loss Bandpass Filters With Ultra-Wideband Isolation Based on Magnetostatic Surface Wave

A new type of nonreciprocal C -band magnetic tunable bandpass filter (BPF) with ultra-wideband (UWB) isolation is presented. The BPF was designed with a 45° rotated yttrium iron garnet (YIG) slab loaded on an inverted-L-shaped microstrip transducer pair. With external in-plane magnetic fields from 1.1 to 1.9 kOe, the central frequency of the filter was tuned from 5.2 to 7.5 GHz, with an insertion loss of 1.6-3 dB and an UWB isolation of more than 20 dB, which was attributed to the nonreciprocity characteristics of the magnetostatic surface wave. In addition, the measured result demonstrated power-handling capabilities of over 30 dBm under room temperature. The proposed prototype with dual functionality of a tunable BPF and an UWB isolator will have many applications in RF front-end and other microwave circuits.

Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance

The broadband microstrip ferromagnetic resonance (FMR), cavity FMR, and Brillouin light scattering spectroscopy techniques have been applied for detection and characterization of a magnetic inhomogeneity in a film sample. In the case of a 100 nm thick permalloy film, an additional magnetically depleted top sublayer has been detected due to pinning effect it produces on the magnetization in the bulk of the film. The pinning results in appearance of an exchange standing spin wave mode in the broadband FMR absorption spectrum, whose amplitudes are different depending on whether the film or the film substrate faces the microstrip transducer. Comparison of the experimental amplitudes for this mode with results of our theory for both film placements revealed that the depleted layer is located at the film surface facing away from the film substrate. Subsequent broadband FMR characterization of a large number of other presumably single-layer films with thicknesses in the range 30–100 nm showed the same result.

Strong asymmetry of microwave absorption by bilayer conducting ferromagnetic films in the microstrip-line based broadband ferromagnetic resonance

Peculiarities of broadband ferromagnetic resonance response of conducting magnetic bilayer films have been studied theoretically. The film thickness was assumed to be smaller than the microwave magnetic skin depth. Excitation of magnetization precession by a homogeneous microwave field incident from one surface of the film has been considered, which mimics the microwave field of a wide microstrip transducer. Strong asymmetry of the response has been found. Depending on the order of layers with respect to the transducer location either the first higher-order standing spin-wave mode or the fundamental mode shows the largest response. This effect is explained as shielding of the transducer field by eddy currents in the films. This shielding remains very efficient for films with thicknesses below the microwave magnetic skin depth. This effect may be useful for studying buried magnetic interfaces and should be accounted for in future development of broadband inductive ferromagnetic resonance methods.

Field-induced transition from parallel to perpendicular parametric pumping for a microstrip transducer

Microstrip transducers used for the excitation of spin waves in magnetic films possess two characteristic properties: high spatial localization of the microwave magnetic field and the presence of field components parallel and perpendicular to the bias field. Here, the effects of these features on the process of parametric pumping are presented. By microwave measurements of the spin-wave instability threshold a transition from parallel pumping to perpendicular pumping at the critical field with the minimal threshold is observed. This transition is accompanied by a sharp threshold increase above the critical field due to the spatial confinement of the pump region.

Spin wave propagation in spatially nonuniform magnetic fields

Spin wave pulse propagation in a magnetic thin film under static, spatially nonuniform magnetic fields has been studied. The experiment was carried out with an yttrium iron garnet film strip. The film strip was magnetized with a spatially nonuniform magnetic field parallel to the length of the film strip. Spin wave pulses were excited with a microstrip transducer at one end of the film strip. The spin wave pulse propagation along the film strip was mapped with a high-resolution time- and space-resolved inductive magnetodynamic probe. The wave number for the spin wave pulses was found to increase in a spatially increasing field and decrease in a spatially decreasing field. The wave number change in a static, general spatially varying static field is reversible for this field-film geometry. The phase velocity was found to decrease in a spatially increasing magnetic field and increase in a spatially decreasing field. The carrier frequency of the spin wave pulses remained constant throughout pulse propagation.

Phase reciprocity of spin-wave excitation by a microstrip antenna

Using space-, time-, and phase-resolved Brillouin light-scattering spectroscopy we investigate the difference in phase of the two counterpropagating spin waves excited by the same microwave microstrip transducer. These studies are performed both for backward volume magnetostatic waves and magnetostatic surface waves in an in-plane magnetized yttrium iron garnet film. The experiments show that for the backward volume magnetostatic spin waves which are reciprocal and excited symmetrically in amplitude there is a phase difference of associated with the excitation process and thus the phase symmetry is distorted. On the contrary, for the magnetostatic surface spin waves which are nonreciprocal and unsymmetrical in amplitude the phase symmetry is preserved there is no phase difference between the two waves associated with the excitation. Theoretical analysis confirms this effect.

Excitation and propagation characteristics of magnetostatic backward volume wave in a double-layered film structure with magnetic damping

The excitation and propagation characteristics of magnetostatic backward volume wave in a double-layered magnetic film structure with magnetic damping are investigated theoretically. The dispersion, the attenuation constant, and the insertion loss can be decreased and the excitation bandwidth can be increased significantly by using a double-layered structure. The propagation constant and the attenuation constant depend strongly on the physical and geometrical parameters of the magnetic film with large thickness. The excitation characteristics are associated not only with the physical and geometrical parameters of the two magnetic layers and the separation layer, but also with the location and geometrical parameters of the microstrip transducer. The effects of the magnetic damping on the radiation resistance and the propagation constant of the magnetostatic wave (MSW) are weak, and the presence of the magnetic damping mainly leads to the propagation loss of the MSW. In addition, the excitation of the MSW is the main bandwidth-limiting mechanism in a double-layered structure.

Full-wave analysis of the excitation of magnetostatic-surface waves by a semi-infinite microstrip transducer - theory and experiment

This paper presents a new method for the complete characterization of the radiation of magnetostatic-surface waves in microstrip transmission lines with longitudinal magnetization. This method is based on the analysis of the excitation of leaky modes in microstrip lines and provides both the propagation constant and the complex impedance of the microstrip. From these quantities, the radiation resistance and other relevant characteristics of the line can be directly obtained.

An analysis of excitation of magnetostatic surface waves in an in-plane magnetized YIG film by the integral kernel expansion method

We present a method to solve a kind of integral equations (we call it the integral kernel expansion method), and apply it to an analysis of excitation of magnetostatic surface-wave/magnetostatic backward-volume-wave modes in a magnetized yttrium-iron-garnet film. The Fourier integral of a normal component of magnetic flux density is derived in terms of an unknown current density flowing in a microstrip transducer. The integral kernel is expanded into a series of the Legendre polynomials and expansion of the unknown current density in terms of appropriate functions reduces the Fourier integral to a system of linear equations with unknown coefficients. Determination of the unknown coefficients allows us to estimate the power of magnetostatic waves, which characterizes the excitation. It is found that our numerical method is superior to the previous conventional method based on an assumed current density. In order to verify the validity of our method, we compare our results with the corresponding experiments, and we have found good agreement between the two.

Measurements of angular and spatial characteristics of magnetostatic wave beams by an optical guided-wave probe

Optical measurements of the angular and spatial characteristics of magnetostatic forward volume wave (MSFVW) beams propagating both in a linear and in a non-linear regime in yttrium–iron–garnet (YIG) film have been performed. The MSFVW beams were excited by a single-element microstrip transducer, within the microwave frequency range 2–3 GHz. The measurements were conducted with the help of an optical probing technique based on the magneto-optical (MO) interaction between guided optical waves and the MSFVWs in the YIG film. The MO probing system was built on the principle of transverse Bragg diffraction geometry, allowing us to measure the spatial evolution of the partial plane waves making up the MSFVW beam. In the linear regime, the measurements of the longitudinal profiles of the partial waves have shown that the MSFVW attenuation coefficient can increase following a linear law, from 2 to 10 cm −1, as the MSFVW wave number increases from 200 to 2000 cm −1. Also, it was shown that MSFVW beams with different frequencies can be spatially separated at a small distance from the microstrip transducer (≈2 mm) by using a weak non-uniform magnetic bias field with a gradient of ≈30 Oe/cm. In the non-linear regime, there are, at least, three specific levels of the incident microwave power which correspond to different manifestations of non-linearity of the MSFVW beams. At a certain value of the power, the partial plane waves of the beam can periodically change the direction of propagation (we observed a periodic collision of these waves). A small increase of the power level can lead to a spatial-periodic energy exchange between the different groups of the partial plane waves. At high microwave powers, non-linear MSFVW can excite a discrete spectrum of new spin-wave modes, the in-plane wave number of which is less than the wave number of the MSFVW. These non-linearly excited waves exist within a small spatial region situated near the microstrip transducer.

Nonlinear ferromagnetic resonance and foldover in yttrium iron garnet thin films-inadequacy of the classical model

A thin-film resonator structure has been used for quantitative measurements of ferromagnetic resonance foldover and the associated bistable power response for yttrium iron garnet (YIG) thin films. The resonator consisted of a 1-mm by 1-mm-square, 4.9 /spl mu/m-thick epitaxial YIG film on top of a 50 /spl mu/m-wide, 3-mm-long microstrip transducer. A static magnetic field of 3200 Oe was applied perpendicular to the film. Low- order magnetostatic forward volume wave standing modes were excited at low power levels in the -20-dBm range and detected as resonance dips in reflected power versus frequency spectra over the range 4-5 GHz. At powers in the 0- to +15-dBm range, these dips showed foldover and bistable response characteristics for increasing and decreasing frequency or power sweeps. The use of 1-10-/spl mu/s-wide pulses instead of continuous-wave (CW) excitation resulted in the consistent disappearance of the foldover and bistability characteristics. The frequency sweep pulse data at fixed power reproduced the down-sweep CW results, and the pulse data for both increasing and decreasing power at fixed frequency reproduced the increasing-power CW results. A quantitative theoretical analysis demonstrates that observed foldover and bistable response characteristics are much weaker than predicted from the classical precession foldover mechanism proposed by Anderson and Suhl, in which the decrease in the static component of the magnetization drives the response. The up-sweep and down-sweep foldover frequency jumps both occur sooner than predicted by this classical mechanism and the calculated foldover profiles are much more severe than the data show.

Measurement of the attenuation constant and the phase propagation constant of magnetostatic surface waves in a microstrip transducer in the 9–9.8GHz range

An experimental investigation was made of an open-ended microstrip transducer which excites a magnetostatic surface wave in the frequency range 9–9.8 GHz in various magnetic fields. A description is given of a method of measuring the input impedance of the transducer in the microwave when an array of connecting waveguide elements with losses were present between the transducer and the resistance measuring system. Dependences of the radiation coefficient and the phase propagation constant of an electromagnetic wave in the transducer were obtained as a function of the magnetic field induction. Calculations were made of the efficiency of conversion of electromagnetic energy into a electromagnetic surface wave.

Theory of MSFVW excitation in a YIG film by a finite-length microstrip transducer

A theoretical study of the excitation of magnetostatic forward volume waves (MSFVW's) in a YIG film by a microstrip transducer of finite length is described. Previous studies of the excitation problem have assumed an infinitely long transducer which is a good assumption at the upper end of the MSFVW spectrum but becomes increasingly unacceptable at the lower end of the spectrum where the MSFVW wavelength is comparable to or larger than the transducer lengths used in practice. The present work reports brute-force numerical computations of MSFVW wavefront mapping and power flow generated by finite-length transducers which are in agreement with expectation.

Wideband optical modulation via the magneto–optic interaction in a bismuth-lutetium-iron garnet film

Optical modulation with a bandwidth of about 3 GHz centered at 5.75 GHz was observed in a thin film of [BiLu]3Fe5O12 using the magneto-optical interaction. A microstrip transducer was placed in contact with the film and TM polarized optical guided modes were excited beneath and parallel to the transducer. The TM→TE mode conversion was measured as a function of the angle between an in-plane field, of up to 100 Oe, and the optical beam. The bandwidth of the modulation was limited by the microwave components used in the external circuit. The experiments qualitatively agree with a simple model that describes a modulation of the optical beam by a nonresonant precession of the magnetization about an equilibrium.

Effect of higher order magnetostatic forward volume wave modes on Bragg diffraction of laser light in a layered yttrium iron garnet film geometry

The present article reports a theoretical study of the TM0⇥TE0 mode conversion of laser light through Bragg diffraction by higher order magnetostatic forward volume waves (MSFVWs) in a layered yttrium iron garnet (YIG) film geometry. It is found that this mode conversion can be significant, thereby somewhat mitigating the previously reported advantage of YIG film layering, i.e., layering affords a significant improvement in the bandwidth for magneto-optic coupling. Computations of the level of magneto-optic (MO) coupling caused by higher order MSFVWs excited by a microstrip transducer in a double YIG film layered structure are presented. The use of a triple YIG film layered geometry with lifted transducers for suppressing the unwanted effect of higher order MSFVW modes on the MO coupling is discussed.

Variations in auto-oscillation frequency at the main resonance in rectangular yttrium–iron–garnet films

High power microwave experiments conducted on a rectangular yttrium-iron-garnet (YIG) film indicate a parabolic dependence of the square of the frequency of auto-oscillations on microwave signal amplitudes, an observation that is qualitatively consistent with prior theoretical predictions. Forward volume magnetostatic waves were excited using a microstrip transducer kept in contact with a YIG film placed in a constant external magnetic field (Hdc=3.48 kG). Variations in the input microwave power (10 dBm<P<25 dBm) and frequency (5.1 GHz<f<5.7 GHz) were used to locate and study auto-oscillations close to the Suhl instability at the main resonance. A novel method of viewing changes in the microwave passband using density plots enables us to study variations in the dipole gaps in the passband near the Suhl instability. A broadening of dipole gaps into fingerlike regions of weak transmission marks the onset of auto-oscillations beyond the instability threshold. These regions are associated with a variety of spin-wave dynamics ranging from simple auto-oscillations to auto-oscillations with period doubling and in some cases an abrupt transition to a turbulent wide-band power spectrum. The parabolic dependence of the auto-oscillation frequency persists despite a period-doubling bifurcation.

Excitation of propagating dipole-exchange spin waves in ferromagnetic double-film structure

A theory of linear excitation of spin waves in perpendicularly magnetized double-film ferromagnetic film structures is developed. Dipole and exchange interaction as well as surface spin pinning conditions are taken into account. Expressions for spin-wave response functions and radiation resistance of a microstrip transducer for the double-film structure are derived. >