19 research outputs found
Epitaxial growth and structural characterization of Pb(Fe1/2Nb1/2)O3 thin films
We have grown lead iron niobate thin films with composition Pb(Fe1/2Nb1/2)O3
(PFN) on (0 0 1) SrTiO3 substrates by pulsed laser deposition. The influence of
the deposition conditions on the phase purity was studied. Due to similar
thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN
perovskite phase. By optimizing the kinetic parameters, we succeeded in
identifying a deposition window which resulted in epitaxial perovskite-phase
PFN thin films with no identifiable trace of impurity phases appearing in the
X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were
smooth and epitaxially oriented with the substrate and as demonstrated by RHEED
streaks which were aligned with the substrate axes. X-ray diffraction showed
that the films were completely c-axis oriented and of excellent crystalline
quality with low mosaicity (X-ray rocking curve FWHM<0.09). The surface
roughness of thin films was also investigated by atomic force microscopy. The
root-mean-square roughness varies between 0.9 nm for 50-nm-thick films to 16 nm
for 100-nm-thick films. We also observe a correlation between grain size,
surface roughness and film thickness.Comment: 13 Pages, 6 figures. To be published in J. Mag. Mag Mater.
proceedings of EMRS200
Multifractal analysis of the electronic states in the Fibonacci superlattice under weak electric fields
Influence of the weak electric field on the electronic structure of the
Fibonacci superlattice is considered. The electric field produces a nonlinear
dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the
nonlinearity is explained in terms of energy levels anticrossings. The
multifractal formalism is applied to investigate the effect of weak electric
field on the statistical properties of electronic eigenfunctions. It is shown
that the applied electric field does not remove the multifractal character of
the electronic eigenfunctions, and that the singularity spectrum remains
non-parabolic, however with a modified shape. Changes of the distances between
energy levels of neighbouring eigenstates lead to the changes of the inverse
participation ratio of the corresponding eigenfunctions in the weak electric
field. It is demonstrated, that the local minima of the inverse participation
ratio in the vicinity of the anticrossings correspond to discontinuity of the
first derivative of the difference between marginal values of the singularity
strength. Analysis of the generalized dimension as a function of the electric
field shows that the electric field correlates spatial fluctuations of the
neighbouring electronic eigenfunction amplitudes in the vicinity of
anticrossings, and the nonlinear character of the scaling exponent confirms
multifractality of the corresponding electronic eigenfunctions.Comment: 10 pages, 9 figure
Investigation of thermally activated flux flow of YBa2Cu3O7/ PrBa2Cu3O7 superlattices in magnetic fields parallel to the a,b plane
Contains fulltext :
112817.pdf (publisher's version ) (Open Access
Ferroic phase transition sequence in epitaxial BiFeO3 thin films
We report a temperature-dependent high-resolution X-ray diffraction investigation of 200 nm epitaxial BiFeO3 thin films grown on (001) SrTiO3. We were successful in making epitaxial thin films thermally stable, a key requirement for this study. Our results provide evidence that BiFeO3 undergoes three high-temperature transitions: an antiferromagnetic transition at 425°C, a first-order α–β phase transition between 745°C and 780°C and a smoother transition toward the γ-phase at 860°C. Both the α–β and β–γ transitions take place 60°C lower than the bulk values whereas the antiferromagnetic transition occurs 55°C higher. This underscores the part played by strain and also emphasizes that BiFeO3 is not a conventional ferroelectric perovskite. Reciprocal space maps reveal the unusual result that the thin films remain monoclinic on crossing the α–β phase transition. Linear extrapolation of the in-plane lattice parameters to higher temperatures rules out cubic symmetry for the γ-phase
Anisotropic magnetotransport in high temperature superconductor multilayers
Contains fulltext :
112800.pdf (publisher's version ) (Open Access
Towards negative capacitance in Pb(Zr0.2Ti0.8)O3 /SrTiO3 superlattices
International audienc
Structural and dielectric investigations of Pb(Zr0.2Ti0.8)O3 /SrTiO3 superlattices
International audienc
Epitaxial high Tc cuprate superlattices: A study of the thermal flux motion
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