Epitaxial Garnets and Hexagonal Ferrites

摘要

The objective of this research is to develop new and improved epitaxial ferrite materials for use in microwave and millimeter-wave signal processing devices. The major emphasis has been on multiple layer magnetic garnet structures for magnetostatic wave (MSW) delay lines. Previous research demonstrated that improved linearly dispersive MSW characteristics (that is, linear variation of delay time with frequency) could be obtained using structures which consisted of two epitaxial magnetic garnet layers separated by an epitaxial nonmagnetic layer. More detailed analysis of the magnetostatic modes in such multiple layer materials was carried out using ferromagnetic resonance (FMR) spectroscopy. This work is aimed at understanding details such as the occurrence of notches in the passband of multiple layer MSW delay lines. A significant problem, common to all MSW delay lines--single layer as well as multiple layer, is the presence of fluctuations in the delay vs. frequency characteristics. These fluctuations, usually called ripple, are attributed reflections of the propagating magnetostatic waves. A new method for suppressing ripple has been devised and demonstrated. In the course of studying epitaxial growth of strontium hexaferrites, a new ferrite material was developed. Crystal growth of gallate spinels for use as substrates for epitaxial growth of lithium ferrite and hexagonal ferrite was continued with further improvements in substrate size. Work on sputter deposition of hexagonal ferrites was initiated.