D. C. Webb

Variable delay lines using magnetostrictive metallic‐glass film overlays

A variable surface acoustic wave (SAW) delay line was fabricated using a thin (<1 μm) magnetostrictive film, metallic‐glass overlay. It is well known that metallic‐glasses can be prepared in ribbon form by rapid quenching from the melt. However, it is difficult to prepare thin film overlays of these materials for SAW and other devices with this technique. We have succeeded in preparing film overlays of Fe‐B by co‐evaporation. Our measured magnetostrictions and magnetizations of these films are virtually the same as in ribbon materials. Delay measurements were made using a vector voltmeter method with a bias magnetic field applied along the direction of SAW propagation and in the two perpendicular directions. The largest delay change is in the plane and perpendicular to the direction of propagation. Although the magnetostriction constants are approximately equal to that of Ni, the changes in delay time, Δτ, in the Fe‐B coated SAW delay lines are larger than for Ni coated SAW devices. Also, much lower satur...

Magnetoelastic surface waves in a magnetic film–piezoelectric substrate configuration

This paper treats the propagation characteristics of magnetoelastic surface waves in a delay line consisting of a ferromagnetic film deposited on a piezoelectric substrate. Magnetoelastic coupling within the film and mechanical coupling between the film and substrate enables the acoustic velocity to be varied by changing the magnetic bias field. A theory to predict the dependence of the surface wave velocity upon applied dc magnetic field, material constants, and frequency is presented. The velocity change occurs predominantly in a bias field range where the static magnetization vectors are undergoing a rotation. The two orientations of the magnetic field in the sagittal plane considered exhibit significantly different characteristics. With the field parallel to the direction of propagation the velocity first decreases, attains a minimum, and then increases toward a saturation value as the external field is increased. With the field normal to the plane of the film, the velocity increases monotonically tow...

Microwave magnetic thin-film devices

The author reviews the current status of magnetic film technology and then summarizes the state-of-the-art and remaining unsolved problems of each of the three major application areas: analog signal processing devices, tunable filters and oscillators, and control components. Two major thin-film approaches are covered: magnetostatic-wave (MSW) devices and thin-film implementations of bulk-ferrite devices. Promising research directions are identified. >

Magnetoelastic surface waves on the (110) plane of highly magnetostrictive cubic crystals

Dispersion characterisitcs of magnetoelastic surface waves in highly magnetostrictive cubic crystals are calculated for different bias fields applied along the direction of propagation. Effects of anisotropy are taken into account. The surface waves are found to be leaky or nonleaky depending on the direction of propagation. Velocity of surface waves is calculated both before and after saturation of the magnetic moment. Although most of the velocity change with bias field occurs while the magnetization vector rotates from the easy direction to the field direction, the velocity changes by a few percent even after the moment saturates. Theoretical results are in good agreement with experiment.

Ferrimagnetic echoes of magnetostatic surface wave modes in ferrite films

This paper presents the first detailed characterization of ferrimagnetic echoes resulting from the nonlinear response of magnetostatic surface waves in a yttrium‐iron‐garnet film to excitation by two time‐resolved rf pulses. Data showing the behavior of the echo as a function of excitation pulse separation time τ, signal pulse power Ps, and pump pulse power Pp is presented. We also show the results of measurements of the spatial variation of the echo response which directly confirm the localized nature of the echo‐producing magnetostatic modes. The data is analyzed in terms of (1) the dispersion relation for magnetostatic surface waves in a dielectric layered structure to obtain the dependence of the echo power on wavenumber and position in the sample and (2) the general properties of echoes produced by the anharmonic response of a system of oscillators to obtain the dependence of the echo power on τ, Ps, and Pp.

Interaction of surface magnetic waves in anisotropic magnetic slabs

Group delay of magnetostatic surface wave propagation in parallel layers of magnetic slabs have been considered. The dispersive characteristics depend strongly on the separation between the slabs and their crystal plane orientations with respect to the applied field ?0 where propagation is normal to ?0 and in the plane of the slab. As an example we consider ?0 along 〈100〉 direction in slab (Slab A) in contact with a metal surface and 〈110〉 direction in the other slab (Slab B) exposed to air. Both slabs are (100) planes. The variation of delay time and bandwidth with relative orientation of the two slabs and their thicknesses are shown. Much larger bandwidth is obtained with two magnetic slabs as compared to that of a single magnetic slab configuration.

Properties of ferrimagnetic echoes in yttrium iron garnet cylinders

The first detailed study of the properties of ferrimagnetic echoes in cylinders of yttrium iron garnet has been performed. Data are presented showing the dependence of the echo on applied field Ha, pulse separation τ, signal pulse power Ps, and pump pulse power Pp. At a given frequency, echoes are found to occur in multiple, well‐defined regions of the parameters τ and Ha. For low Ps and Pp, the echo power Pe increases linearly with increasing Ps but increases very rapidly with increasing Pp, following Pe∼P4.5p. Pe saturates at high power levels with the saturation level depending on both Ps and Pp. Additional experimental observations, which give further insight into the excitation and evolution of the echo, are also presented. Experimental results verify some of the qualitative predictions of various models previously proposed for the ferrimagnetic echo process but also point out some of the limitations of these models.

Magnetoelastic surface wave propagation in a low‐anisotropy rare‐earth–iron compound at 80 MHz

Propagation of 80‐MHz surface acoustic waves on a single‐crystal substrate of Ho0.58Tb0.20Dy0.22Fe2 in the presence of a magnetic field is reported. Phase velocity changes of 2%, accompanied by attenuation changes in excess of 30 dB, have been observed by varying the applied magnetic field. Measurements of velocity and attenuation variation with field magnitude and direction are presented along with qualitative explanations of the observed experimental behavior.

Minimization of the noise temperature of the free‐electron bolometer mixer

The principal factors which limit the bandwidth and noise temperature of the free‐electron bolometer mixer have been calculated. The minimum mixer contribution to the effective noise temperature is found to be 33Tlattice under the conditions of rf match, IF match, and constant current bias. This result is independent of the electron‐lattice energy relaxation time, and can be achieved without significantly degrading the information bandwidth. The best experimental values from the literature are found to be near this predicted performance.

Magnetic Control of Surface Eiastic Waves in a Novel Layered Structure

In this paper we describe theoretical and experimental results for magnetoelastic surface wave propagation in a new layered structure consisting of a ferromagnetic film deposited on a piezoelectric substrate between two interdigital transducers. The surface wave velocity in this structure can be varied continuously by adjusting an external d.c. magnetic field. The velocity change occurs predominantly in the bias field range where the static magnetization vectors are undergoing rotation. We consider three different orientations of the external field both tangential and normal to the plane of the film. Propagation characteristics are significantly different in the three orientations. The calculated velocity changes are in good agreement with changes measured on a Ni–LiNbO3 delay line.