A perspective on magnetic materials for bubble mass memories

Recent advances in the liquid phase epitaxial growth of rare earth magnetic garnet films have enhanced prospects for a bubble mass memory. It is the purpose of this paper to review the status of materials in order to achieve some perspective. Principal problems are those of uniformity, reproducibility, and defect control. Good uniformity of LPE films has been achieved. Recent phase diagram data based on the garnet oxides in PbO-B2O3fluxes show that high orders of compositional and growth temperature control are required for reproducibility but are within the state of the art. Defect control, which is closely related to dislocation formation, seems not to be a limiting problem, attributable largely to the high energy of formation of dislocations in the garnets. Thus, even interfacial or mismatch dislocations do not form in these heteroepitaxial structures.