Epitaxial Hexagonal Ferrites for Millimeter Wave Tunable Filters

This program has consisted of an investigation of the liquid phase epitaxial growth of hexagonal ferrites. The objective has been to obtain high quality single crystal layers of hexagonal ferrite which would be suitable for use in millimeter-wave tunable filters. The specific objectives were to determine the conditions required for preparation of ferrites which would give ferromagnetic resonance at frequencies in the range of 50 to 70 GHz using magnetic bias fields available with present technology and having resonance linewidths no greater than 50 0e. The work consisted of the growth and preparation of gallate spinel substrate crystals, the liquid phase epitaxial growth of strontium hexaferrite layers on these substrates by means of a lead oxide - boron oxide flux, and the characterization of these materials. Techniques were devised for fairly reproducible growth of hexaferrites which had linewidths substantially less than 100 0e and which required fields of only about 7 K0e for resonance at 60 GHz. The best sample had a linewidth of 60 0e, a significant improvement over previous epitaxial hexaferrites. (Author)