93 research outputs found
Antiferromagnetism at the YBa2Cu3O7 / La2/3Ca1/3MnO3 interface
The magnetic properties of a series of YBa2Cu3O7-x/La2/3Ca1/3MnO3
(YBCO/LC1/3MO) superlattices grown by dc sputtering at high oxygen pressures
(3.5 mbar) show the expected ferromagnetic behaviour. However, field cooled
hysteresis loops at low temperature show the unexpected existence of exchange
bias, effect associated with the existence of ferromagnetic/antiferromagnetic
(F/AF) interfaces. The blocking temperature (TB) is found thickness dependent
and the exchange bias field (HEB) is found inversely proportional to the FM
layer thickness, as expected. The presence of an AF material is probably
associated to interface disorder and Mn valence shift towards Mn4+.Comment: 12 pages, 2 figures, 1 table, submitted to Applied Physics Letter
Improving HTc Josephson Junctions (HTc JJ) by annealing: the role of vacancy-interstitial annihilation
We have studied the annealing effect in transport properties of High
temperature Josephson Junctions (HTc JJ) made by ion irradiation. Low
temperature annealing (80 degrees Celsius) increases the JJ transition
temperature (TJ) and the Ic.Rn product, where Ic is the critical current and Rn
the normal resistance. We found that the spread in JJ characteristics can be
lowered by sufficient long annealing times. Using random walk numerical
simulations, we showed that the characteristic annealing time and the evolution
of the spread in JJ characteristics can be explained by a vacancy-interstitial
annihilation process rather than by an oxygen diffusion one.Comment: 7 pages and 3 figures submitted to Applied Physics Letter
Study and optimization of ion-irradiated High-Tc Josephson nanoJunctions by Monte Carlo simulations
High Tc Josephson nanoJunctions (HTc JnJ) made by ion irradiation have
remarkable properties for technological applications. However, the spread in
their electrical characteristics increases with the ion dose. We present a
simple model to explain the JnJ inhomogeneities, which accounts quantitatively
for experimental data. The spread in the slit's width of the irradiation mask
is the limiting factor.Monte Carlo simulations have been performed using
different irradiation conditions to study their influence on the spread of the
JnJ charcateristics. A "universal" behavior has been evidenced, which allows to
propose new strategies to optimize JnJ reproducibility.Comment: 14 pages, 6 Figures. accepted in Journal of Applied Physic
Influence of ion implantation on the magnetic and transport properties of manganite films
We have used oxygen ions irradiation to generate controlled structural
disorder in thin manganite films. Conductive atomic force microscopy CAFM),
transport and magnetic measurements were performed to analyze the influence of
the implantation process in the physical properties of the films. CAFM images
show regions with different conductivity values, probably due to the random
distribution of point defect or inhomogeneous changes of the local Mn3+/4+
ratio to reduce lattice strains of the irradiated areas. The transport and
magnetic properties of these systems are interpreted in this context.
Metal-insulator transition can be described in the frame of a percolative
model. Disorder increases the distance between conducting regions, lowering the
observed TMI. Point defect disorder increases localization of the carriers due
to increased disorder and locally enhanced strain field. Remarkably, even with
the inhomogeneous nature of the samples, no sign of low field magnetoresistance
was found. Point defect disorder decreases the system magnetization but doesn t
seem to change the magnetic transition temperature. As a consequence, an
important decoupling between the magnetic and the metal-insulator transition is
found for ion irradiated films as opposed to the classical double exchange
model scenario.Comment: 27 pages, 11 Figure
Direct observation of electronic inhomogeneities induced by point defect disorder in manganite films
We have investigated the influence of point defect disorder in the electronic
properties of manganite films. Real-time mapping of ion irradiated samples
conductivity was performed though conductive atomic force microscopy (CAFM).
CAFM images show electronic inhomogeneities in the samples with different
physical properties due to spatial fluctuations in the point defect
distribution. As disorder increases, the distance between conducting regions
increases and the metal-insulator transition shifts to lower temperatures.
Transport properties in these systems can be interpreted in terms of a
percolative model. The samples saturation magnetization decreases as the
irradiation dose increases whereas the Curie temperature remains unchanged
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