128 research outputs found
Nanoscale studies of domain wall motion in epitaxial ferroelectric thin films
Atomic force microscopy was used to investigate ferroelectric switching and
nanoscale domain dynamics in epitaxial PbZr0.2Ti0.8O3 thin films. Measurements
of the writing time dependence of domain size reveal a two-step process in
which nucleation is followed by radial domain growth. During this growth, the
domain wall velocity exhibits a v ~ exp[-(1/E)^mu] dependence on the electric
field, characteristic of a creep process. The domain wall motion was analyzed
both in the context of stochastic nucleation in a periodic potential as well as
the canonical creep motion of an elastic manifold in a disorder potential. The
dimensionality of the films suggests that disorder is at the origin of the
observed domain wall creep. To investigate the effects of changing the disorder
in the films, defects were introduced during crystal growth (a-axis inclusions)
or by heavy ion irradiation, producing films with planar and columnar defects,
respectively. The presence of these defects was found to significantly decrease
the creep exponent mu, from 0.62 - 0.69 to 0.38 - 0.5 in the irradiated films
and 0.19 - 0.31 in the films containing a-axis inclusions.Comment: 13 pages, 15 figures, to be published in J. App. Phys. special issue
on ferroelectric
Structural phases driven by oxygen vacancies at the La0.7Sr0.3MnO3/SrTiO3 hetero-interface
An oxygen vacancy driven structural response at the epitaxial interface between La0.7Sr0.3MnO3 films and SrTiO3 substrates is reported. A combined scanning transmission electron microscopy and electron energy loss spectroscopy study reveal the presence of an elongated out-of-plane lattice parameter, coupled to oxygen vacancies and reduced manganese oxidation state at the La0.7Sr0.3MnO3 side of the interface. Density functional theory calculations support that the measured interface structure is a disordered oxygen deficient brownmillerite structure. The effect of oxygen vacancy mobility is assessed, revealing an ordering of the vacancies with time
Controlling the switching field in nanomagnets by means of domain-engineered antiferromagnets
Using soft x-ray spectromicroscopy, we investigate the magnetic domain
structure in embedded nanomagnets defined in LaSrMnO thin
films and LaFeO/LaSrMnO bilayers. We find that
shape-controlled antiferromagnetic domain states give rise to a significant
reduction of the switching field of the rectangular nanomagnets. This is
discussed in the framework of competition between an intrinsic spin-flop
coupling and shape anisotropy. The data demonstrates that shape effects in
antiferromagnets may be used to control the magnetic properties in nanomagnets
Width distribution of contact lines on a disordered substrate
We have studied the roughness of a contact line of a liquid meniscus on a
disordered substrate by measuring its width distribution. The comparison
between the measured width distribution and the width distribution calculated
in previous works, extended here to the case of open boundary conditions,
confirms that the Joanny-de Gennes model is not sufficient to describe the
dynamics of contact lines at the depinning threshold. This conclusion is in
agreement with recent measurements which determine the roughness exponent by
extrapolation to large system sizes.Comment: 4 pages, 3 figure
Quantum Information Processing with Ferroelectrically Coupled Quantum Dots
I describe a proposal to construct a quantum information processor using
ferroelectrically coupled Ge/Si quantum dots. The spin of single electrons form
the fundamental qubits. Small (<10 nm diameter) Ge quantum dots are optically
excited to create spin polarized electrons in Si. The static polarization of an
epitaxial ferroelectric thin film confines electrons laterally in the
semiconductor; spin interactions between nearest neighbor electrons are
mediated by the nonlinear process of optical rectification. Single qubit
operations are achieved through "g-factor engineering" in the Ge/Si structures;
spin-spin interactions occur through Heisenberg exchange, controlled by
ferroelectric gates. A method for reading out the final state, while required
for quantum computing, is not described; electronic approaches involving single
electron transistors may prove fruitful in satisfying this requirement.Comment: 10 pages, 3 figure
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