C. Vittoria

Applications of amorphous magnetic-layers in surface-acoustic-wave devices

This paper reviews the theory and potential applications of magnetically variable delay lines and oscillators which employ a magnetostrictive film on a piezoelectric surface-acoustic-wave (SAW) substrate. Cases analyzed in detail indicate that the delay change arises mainly from a rotation of the magnetic moment from the films easy axes toward the applied field direction; thus the interaction is essentially nondispersive. Use of amorphous metallic-glass overlays is particularly attractive because their high magnetostriction and low magnetic anisotropy makes a relatively large delay variation possible with a small change in bias field. Since the SAW velocity can be changed only by sim .1 % or less with present film technology, applications are restricted to those where only a small frequency or delay adjustment is required. Two prototype examples are considered in detail--a variable delay line for steering an adaptive array antenna and a tunable resonator oscillator capable of tracking high speed Doppler targets. In both of these examples, the magnetic film/SAW substrate geometry is seen to be an attractive alternative to competitive approaches.

Induced in-plane magnetic anisotropy in YIG films

We have studied the symmetry properties of the in-plane induced magnetic anisotropy in {100} and {110} disks of single crystal YIG epitaxially grown on gadolinium gallium garnet (GGG) substrates. The ferromagnetic resonance (FMR) technique was used to determine the values of the cubic and induced magnetic anisotropies. The induced anisotropy is interpreted in terms of a magnetostrictive magnetic potential energy. We find that the effective field induced in the plane of the film is isotropic for {100} disks but for {110} disks the induced anisotropy is uniaxial within the plane.

FMR in some amorphous Re ‐ 3‐d transition metal films

Ferrimagnetic Resonance (FMR) and vibrating sample magnetometer (VSM) measurements were made on amorphous GdCo3 and Gd‐, Ho‐, Tb‐ and DyFe2 for temperatures from 90 to 500K. For Gd alloys, the T dependence of the linewidth is in general agreement with that predicted for a T independence Landau‐Lifshitz damping parameter of ∠198/s. Ho‐ and TbFe2 and to a lesser degree the Gd alloys show inconsistencies between the FMR and VSM values for the magnetization.

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.

Thermal annealing in irradiated garnet films

Effects of thermal annealing on the uniaxial magnetic anisotropy field, H A , of irradiated bubble garnet materials have been measured. Techniques of ferrimagnetic resonance (FMR) and stripe lattice resonance (SLR) were used in measuring changes in H A as a function of annealing temperature. The annealing temperature (T A ) was varied from 20 to 800 C. We find that H A changes in magnitude by as much as 1000 Oe and also changes from negative to positive value as the annealing temperature is increased from room temperature. For T A A is proportional to the irradiation dosage level.

Magnetic Wave Propagation in YIG and Lithium Ferrite Slabs

Propagation losses are calculated for magnetostatic surface waves in slabs of cubic magnetic materials. A phenomenological (Gilbert) magnetic damping is assumed and cubic magnetic anisotropy is included in the calculations. The dispersion relations are derived for a geometry in which a ferrite slab is separated from a ground plane by a non‐magnetic dielectric layer1. Delay time, attenuation constant and a loss factor L(dB/μ‐sec) are calculated as a function of frequency for YIG and lithium ferrite. The calculated values for YIG are in reasonable agreement with recent measurements2.

The Effects of Magnetic Anisotropy on Magnetostatic Modes in Epitaxial YIG Discs

We have made in‐plane ferromagnetic resonance measurements at X‐band on single crystal YIG discs epitaxially grown on GGG substrates. The in‐plane resonant fields of the magnetostatic spectrum were measured as a function of aspect ratio, temperature, angle, and crystal plane ([110] or [100]). The aspect ratio ranged from 25 to 500 while the temperature of the samples was held at 77°K, and 300°K.

Magnetic properties of Gd1−xFex films

The saturation magnetization, M, g‐value, exchange and magnetic damping parameter were measured in films of Gd1−xFex, where 0<x<1, as a function of temperature and frequency using ferromagnetic resonance (FMR) and vibrating samples magnetometer techiques. We find for x∠.9 that the dominant exchange coupling is between the Fe‐Fe ions. The exchange‐conductivity linewidth broadening mechanism is minimal in this sytem.

Magnetically tunable band-pass filter utilizing coplanar-slotline junction

A tunable bandpass filter using a yttrium-iron-garnet (YIG) disk and a coplanar-slotline structure is proposed. The filter is tunable from 0.76 to 14.5 GHz. Over this band of frequencies the maximum insertion loss was 4.9 dB and the minimum loss was 1.7 dB. The planar-type device is well suited for the microwave integrated circuit (MIC) planar technology. >

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.