Evaluation of Single-Crystal Planar Hexagonal Ferrites for Application to Microwave Devices

摘要

To satisfy Army device requirements in radar, countermeasures, and satellite systems between 9 and 140 kMc, a wide variety of nonlinear, ferromagnetic components such as power limiters, tunable filters, and pulsed, ferromagnetic generators must be designed and constructed. Such devices, presently restricted because of an inherent frequency limitation or the prohibitively large d-c field requirement, demand a material with unique properties (high magnetic anisotropy) to permit efficient device operation with small, applied fields. After several years of research and development, single crystals of ZnY (Ba2Zn2Fe2O3), modified by substituted manganese, have yielded crystals with a resonance linewidth of 3.8 oersteds at 9.0 kMc and room temperature. This represents the lowest value reported for planar, hexagonal ferrites. From the observed threshold field, a spin-wave linewidth of 1.24 oersteds was calculated. An experimental subsidiary resonance limiter at 17.2 kMc was designed and its characteristics are being evaluated using Mn-ZnY crystals. At Ku-band frequencies and above, d-c magnetic field requirements are smaller for Mn-ZnY than for yttrium-iron-garnet, permitting a smaller, lighter device. (Author)