Backward Volume Magnetostatic Waves Research Articles

Experimental study of microwave magnetostatic waves in thin-film yttrium-iron-garnet with a new magnetic-induction probe

A new high spatial-resolution magnetic-induction probe that measures microwave magnetic field patterns of magnetostatic waves in ferrite thin films has been developed. The probe’s sensing element is either a strand of 25.4-μm-diam gold wire wrapped around a plastic support or an aluminum rectangular loop photolithographically fabricated on glass. The gold wire method yielded a smallest size of 120 μm, and the aluminum loops achieved a highest resolution of 45 μm. The probe is designed for studies of amplitude profiles, dispersion relations, and phase-propagation direction. Investigations of magnetostatic surface waves (MSSW) and backward volume waves (MSBVW) propagating in liquid-phase epitaxially (LPE) grown yttrium-iron-garnet (YIG) were conducted. The LPE-YIG sample used was 4.5 μm thick with the [111] direction perpendicular to the surface of the sample. MSSW and MSBVW of 2–4 GHz microwave frequency were launched in the LPE-YIG, 4.1° from the [01̄1] direction. Studies of MSSW were done under uniform and nonuniform in-plane magnetic bias fields. When contrasted to expected spreading due to diffraction, MSSW in uniform bias fields were found to ‘‘focus’’ as the wave propagated. The ‘‘focusing’’ effect was determined by measurement of the microwave magnetic field profile, transverse to the phase-propagation direction, as a function of propagation distance. As the MSSW propagated, the peak value of the profile increased while the profile width decreased until a maximum profile amplitude occurred, after which the MSSW decreased in amplitude and the width increased. With MSSW and MSBVW in constant uniform bias fields, direct measure of the wavelengths at various microwave frequencies yielded the dispersion relation for each type of wave. Determination of the dispersion relation of MSBVW confirmed the backward nature of these waves.

Magnetostatic backward waves in low dose ion implanted YIG films

Magnetostatic backward volume wave (MSBVW) delay measurements are reported on a 4.8 µm thick YIG film ion implanted at a low dose (3× 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> ions/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) by a 320 keV beam of single ionized helium atoms ( He+). Nonuniform magnetization and uniaxial anisotropy profiles are used to model the ion implanted film. Calculated results fit the experimental data well. Expressions for the bias permeability tensor elements excluding crystalline (cubic) anisotropy are presented. A method is proposed to better characterize the magnetic properties of ferrimagnetic thin films. This method is applied to separate the uniaxial anisotropy field from the magnetization.

Effect of the direction of biasing field on magnetostatic volume wave delays

An investigation of the effect of the direction of a dc biasing field on the magnetostatic volume wave delays in YIG sandwiched between two ground planes has been made. Specifically, the magnetic field has been assumed to be arbitrary in three planes: (a) forward volume wave to backward volume plane; (b) forward volume wave to surface wave plane; (c) backward volume wave to surface wave plane. A general dispersion relation has been derived. The numerical results indicate that delays can be controlled by the direction of the dc magnetic field. The effect of the thickness of the dielectric on the delay characteristics of magnetostatic backward volume waves has also been studied. The present study shows that a suitable filter can be designed, whose bandwidth may be varied by rotating the direction of the magnetic field.

Examination of magnetostatic waves by new optical and induction probes

New optical and induction probes have been developed and used to investigate microwave (1–4 GHz) magnetostatic waves (MSW) propagating in yttrium iron garnet (YIG) thin films (5–50 μm). The optical probe uses the magnetooptic properties of YIG, and light from a 45 mW, 1.15 μm HeNe laser, to examine rfmagnetization of MSW. Focused light for localized probing has achieved a spatial resolution of 100 μm. The induction probe senses the rf magnetic field, which fringes from the surface of YIG thin films, with metal loops of either gold wire wrapped around a plastic support or aluminum photolithographically fabricated on glass. The highest spatial resolution was attained with 45μm aluminum loops. The optical probe has been used to examine the amplitude of linear and nonlinear forward volume waves (MSFVW). Nonlinear effects are characterized by MSFVW saturation and then a decline as input power to the wave increased. Localized probing of nonlinear properties showed, that over small regions, a monotonic increase of light modulation with increasing microwave input power to MSFVW does not always occur. MSFVW in the linear regime were studied for evolution of the amplitude profile as it propagated from the launching antenna. Magnetostatic surface (MSSW) and backward volume (MSBVW) waves have been explored with the induction probe for amplitude and dispersion relation. In a uniform bias field, an apparent form of spatial focusing was exhibited by MSSW. Direct measure of wavelengths of MSSW and MSBVW gave the dispersion relations.

Suppression of magnetostatic backward volume wave end reflections via field gradients

This paper reports the use of longitudinal magnetic field variations to suppress magnetostatic backward volume wave end reflections in an yttrium-iron-garnet (YIG) thin film. The variations were achieved by mounting the YIG film between two mumetal strips. The passband ripple in the insertion loss due to reflections was reduced from an average of about 12 dB peak to peak to 1/2 dB peak to peak with this technique.

Propagation characteristics of magnetostatic waves

The present paper reviews the propagation characteristics of the three magnetostatic wave-types that can exist in a ferrimagnetic film such as the commonly used epitaxial yttrium-iron-garnet (YIG) film, viz., magnetostatic surface waves (MSSWs), magnetostatic forward volume waves (MSFVWs) and magnetostatic backward volume waves (MSBVWs). The pronounced inherent dispersiveness of these waves and methods of controlling or tailoring dispersion are discussed. Other propagation characteristics such as diffraction and propagation loss and the envelope distortion of acw pulse in propagating through such a dispersive medium are briefly described.

4987. Beams steering and diffraction of magnetostatic backward volume waves: S P Parekh and H S Tuan, J Appl Phys, 52 (3), 1981, 2279–2281

4987. Beams steering and diffraction of magnetostatic backward volume waves: S P Parekh and H S Tuan, J Appl Phys, 52 (3), 1981, 2279–2281

Microwave diplexer using magnetostatic surface and backward volume waves

An experimental diplexer based on magnetostatic wave propagation in a tangentially magnetised thin film of YIG is reported. The diplexer function is obtained by using the fact that magnetostatic surface and backward volume waves propagate in contiguous but nominally nonoverlapping frequency bands.

Beams steering and diffraction of magnetostatic backward volume waves

This paper reports theoretical calculations of the beam spreading of magnetostatic backward volume waves (MSBVW’s) arising from the finite length of practical transducers. The calculations include the beam steering effects resulting from the pronounced anisotropy of MSBVW propagation. The predicted beam spreading of MSBVW’s is significantly larger than that of SAW’s on YZ LiNbO3. On the other hand, based on comparison with reported experimental results on the beam spreading of magnetostatic surface waves (MSSW’s), it would appear that MSBVW’s suffer smaller beam spreading than MSSW’s.

Excitation of magnetostatic backward volume waves

This paper reports a theory for the electromagnetic transduction properties of magnetostatic backward volume waves (MSBVW's). The basic problem treated is that the MSBVW excitation by the most basic electromagnetic transducer, viz., a line-current source. The excitation characteristics of a practical extended transducer in the form of a microstrip are synthesized from the line-current source results. The frequency variation of the radiation resistance and reactance of these transducers is calculated over the entire magnetostatic volume wave (MSVW) spectrum. At the high-frequency end of the spectrum, MSBVW excitation by a microstrip is the strongest and comparable to magnetostatic forward volume wave (MSFVW) excitation obtaining at the opposite (or low-frequency) end of the spectrum. While the line-current source yields significant excitation of higher-order MSBVW's, with a microstrip, because of the array effects associated with the extended geometry of a microstrip in relation to the line-current source, the higher-order modes are strongly suppressed.

M.S.W. nondispersive, electronically tunable time delay elements

A nondispersive, electronically tunable (165-180 ns) time delay unit based on magnetostatic wave (m.s.w.) propagation with 6% bandwidth at 3 GHz has been demonstrated. The unit is implemented by cascading magnetostatic surface wave and magnetostatic backward volume wave delay lines designed so that the dispersion slopes are equal and opposite in slope over the common operating bandwidth; this produces an element with constant time delay over the bandwidth which can be adjusted by a bias field variation of one of the lines.