254 research outputs found
Hysteresis in the electronic transport of V2O3 thin films: non-exponential kinetics and range scale of phase coexistence
The thermal hysteresis of the electronic transport properties were studied
for V2O3 thin films. The temporal evolution of the resistance shows the
out-of-equilibrium nature of this hysteresis with a very slow relaxation.
Partial cycles reveal not only a behavior consistent with phase coexistence,
but also the presence of spinodal temperatures which are largely separated. The
temperature spreading of phase coexistence is consistent with the bulk phase
diagram in the pressure-temperature plane, confirming that the film is
effectively under an effective pressure induced by the substrate.Comment: Accepted for publication in Europhysics Letter
The role of ferroelectric-ferromagnetic layers on the properties of superlattice-based multiferroics
A series of superlattices and trilayers composed of ferromagnetic and
ferroelectric or paraelectric layers were grown on (100) SrTiO3 by the pulsed
laser deposition technique. Their structural and magneto-electric properties
were examined. The superlattices made of ferromagnetic Pr0.85Ca0.15MnO3 (PCMO)
and a ferroelectric, namely Ba0.6Sr0.4TiO3 (BST) or BaTiO3, showed enhanced
magnetoresistance (MR) at high applied magnetic field, whereas such enhancement
was absent in Pr0.85Ca0.15MnO3/SrTiO3 superlattices, which clearly demonstrates
the preponderant role of the ferroelectric layers in this enhanced MR.
Furthermore, the absence of enhanced MR in trilayers of PCMO/BST indicates that
the magneto-electric coupling which is responsible for MR in these systems is
stronger in multilayers than in their trilayer counterparts.Comment: to be published in J. Appl. Phy
Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study
High quality ZnO thin films were gown using the pulsed laser deposition
technique on (0001) AlO substrates in an oxidizing atmosphere, using a
Zn metallic target. We varied the growth conditions such as the deposition
temperature and the oxygen pressure. First, using a battery of techniques such
as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force
microscopy, we evaluated the structural quality, the stress and the degree of
epitaxy of the films. Second, the relations between the deposition conditions
and the structural properties, that are directly related to the nature of the
thin films, are discussed qualitatively. Finally, a number of issues on how to
get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004
Influence of the microstructure on the magnetism of Co-doped ZnO thin films
The prediction of ferromagnetism at room temperature in Co-ZnO thin films has
generated a large interest in the community due to the possible applications.
However, the results are controversial, going from ferromagnetism to
non-ferromagnetism, leading to a large debate about its origin (secondary
phase, Co clusters or not). By carefully studying the micro-structure of
various Co-ZnO films, we show that the Co2+ partly substitutes the ZnO wurtzite
matrix without forming Co clusters. Surprisingly, the ferromagnetism nature of
the films disappears as the Co content increases. In addition, our results
suggest that the observed ferromagnetism is likely associated to a large amount
of defects- close to the interface and strongly depending on the growth
temperature- which may explained the spreading of the results.Comment: 4 pages, 4 figures, to be published in Journal of Applied Physics
(2006
Control of the colossal magnetoresistance by strain effect in NdCaMnO thin films
Thin films of NdCaMnO manganites with colossal
magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser
Deposition technique on (100)-SrTiO. The lattice parameters of these
manganites and correlatively their CMR properties can be controlled by the
substrate temperature . The maximum CMR effect at 75K, calculated as the
ratio is 10 for a deposition temperature of
degC. Structural studies show that the
NdCaMnO film is single phase, [010]-oriented and has a
pseudocubic symmetry of the perovskite subcell with a=3.77 at room
temperature. We suggest that correlation between lattice parameters, CMR and
substrate temperature result mainly from substrate-induced strains
which can weaken the charge-ordered state at low temperature.Comment: 9 pages, 4 figures. To be published in Applied Physics Letter
Structure determination of a brownmillerite Ca2Co2O5 thin film by Precession Electron Diffraction
Calcium cobaltite thin films with a ratio Ca/Co=1 were grown on (101)-NdGaO3
substrate by the pulsed laser deposition technique. The structure of the
deposited metastable phase is solved using a precession electron diffraction 3D
dataset recorded from a cross-sectional sample. It is shown that an ordered
oxygen-deficient Ca2Co2O5+d perovskite of the brownmillerite-type with lattice
parameters a= 0.546nm, b=1.488nm and c=0.546nm (SG: Ibm2) has been stabilized
using the substrate induced strain. The structure and microstructure of this
metastable cobaltite is further discussed and compared to related bulk
materials based on our transmission electron microscopy investigationsComment: 13 pages, 10 figures, 2 tables, accepted in Phys. Rev.
Strain induced pressure effect in pulsed laser deposited thin films of the strongly correlated oxide V2O3
V2O3 thin films about 10 nm thick were grown on Al2O3 (0001) by pulsed laser
deposition. The XRD analysis is in agreement with R-3c space group. Some of
them exhibit the metal / insulator transition characteristic of V2O3 bulk
material and others samples exhibit a metallic behavior. For the latter, the
XPS analysis indicates an oxidation state of +III for vanadium. There is no
metal / insulator transition around 150 K in this sample and a strongly
correlated Fermi liquid rho = AT2 behavior of the resistivity at low
temperature is observed, with a value of A of 1.2 10-4 ohm cm, 3 times larger
than the bulk value at 25 kbar
Epitaxial Growth of LaSrFeO thin films by laser ablation
We report on the synthesis of high quality LaSrFeO (LSFO)
thin films using the pulsed laser deposition technique on both SrTiO (STO)
and LaAlO (LAO) substrates (100)-oriented. From X-Ray diffraction (XRD)
studies, we find that the films have an out-of-plane lattice parameter around
0.3865nm, almost independent of the substrate (i.e. the nature of the strains).
The transport properties reveal that, while LSFO films deposited on STO exhibit
an anomaly in the resistivity vs temperature at 180K (corresponding to the
charge-ordered transition and associated with a transition from a paramagnetic
to an antiferromagnetic state), the films grown on LAO display a very small
magnetoresistance behavior and present an hysteresis around 270K under the
application of a 4T magnetic field. The changes in transport properties between
both substrates are discussed and compared with the corresponding single
crystals.Comment: 9 pages, 4 figure
Structural and magnetic properties of a series of low doped ZnCoO thin films deposited from Zn and Co metal targets on (0001) AlO substrates
We report on the synthesis of low doping ZnCoO () thin
films on (0001)-AlO substrates. The films were prepared in an oxidizing
atmosphere, using the pulsed laser deposition technique starting from Zn and Co
metallic targets. We first studied the influence of the strains of ZnO and
their stuctural properties. Second, we have investigated the structural and the
magnetic properties of the ZnCoO films. We show that at low doping,
the lattice parameters and the magnetization of the ZnCoO films
depend strongly on the Co concentration.Comment: to be published in Journal Applied Physics (June 2004) as a
proceeding of the MMM/Intermag Conferenc
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