Dennis F. Dungan

Applicability of effective medium theory to ferroelectric/ferrimagnetic composites with composition and frequency‐dependent complex permittivities and permeabilities

High‐frequency (1 MHz–1 GHz) transmission line measurements were used to determine the composition and frequency‐dependent complex permittivities and complex permeabilities of ferroelectric/ferrimagnetic (barium titanate and a magnesium‐copper‐zinc ferrite) composites. The effective medium rules of Maxwell–Garnett give both lower and upper bounds for the effective permittivities and permeabilities and yield accurate estimates of the bulk electric and magnetic properties at low volume fill fraction of either component provided the proper host matrix is chosen. Bruggeman theory yielded the best predictive values for the permittivity and permeability over the entire composition range. In all cases these complex quantities were shown to be constrained by Bergman–Milton bounds.

Formation of thin‐film high Tc superconductors by metalorganic deposition

Metalorganic deposition (MOD) is a nonvacuum method of thin‐film deposition which allows easy alteration of chemical components and is compatible with thin‐film processing. We report the preparation of thin‐film superconductors by MOD. Rutherford backscattering spectrometry was used to determine film compositions and thicknesses. Films, approximately 500 nm thick, of YBa2Cu4Oz (z undetermined) were deposited on 〈100〉 single‐crystal SrTiO3. A superconducting onset temperature of 90 K was measured with 37 K the zero resistance temperature. Scanning electron microscopy revealed grain sizes approximately 250 nm in diameter.