392 research outputs found
Local Dielectric Measurements of BaTiO3-CoFe2O4 Nano-composites Through Microwave Microscopy
We report on linear and non-linear dielectric property measurements of BaTiO3
- CoFe2O4 (BTO-CFO) ferroelectro-magnetic nano-composites and pure BaTiO3 and
CoFe2O4 samples with Scanning Near Field Microwave Microscopy. The permittivity
scanning image with spatial resolution on the micro-meter scale shows that the
nano-composites have very uniform quality with an effective dielectric constant
\epsilon_r = 140 +/- 6.4 at 3.8 GHz and room temperature. The temperature
dependence of dielectric permittivity shows that the Curie temperature of pure
BTO was shifted by the clamping effect of the MgO substrate, whereas the Curie
temperature shift of the BTO ferroelectric phase in BTO-CFO composites is less
pronounced, and if it exists at all, would be mainly caused by the CFO.
Non-linear dielectric measurements of BTO-CFO show good ferroelectric
properties from BTO.Comment: 6 pages, 6 figures, to be published in the Journal of Materials
Researc
Spatially Resolved Nonlinearity Measurements of YBaCuO Bi-crystal Grain Boundaries
We have developed a near-field microwave microscope to locally excite a
superconducting film and measure second and third harmonic responses at
microwave frequencies. We study the local nonlinear response of a
YBaCuO thin film grown on a bi-crystal SrTiO substrate. The
location of the bi-crystal grain boundary is clearly identified by the
microscope through higher harmonic response, and the spatial resolution is on
the order of the magnetic loop probe size, about 500. The harmonic power
and spatial resolution are successfully modeled with a one-dimensional extended
Josephson junction simulation. From the model, the 2nd order harmonic response
is dominated by Josephson vortex generation and flow. A geometry-free nonlinear
scaling current density is also exstracted
from the data, indicating that the grain boundary weak link is the dominant
nonlinear source in this case.Comment: 4pages, 4figure
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