45 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
Magnetization reversal and anomalous coercive field temperature dependence in MnAs epilayers grown on GaAs(100) and GaAs(111)B
The magnetic properties of MnAs epilayers have been investigated for two
different substrate orientations: GaAs(100) and GaAs(111). We have analyzed the
magnetization reversal under magnetic field at low temperatures, determining
the anisotropy of the films. The results, based on the shape of the
magnetization loops, suggest a domain movement mechanism for both types of
samples. The temperature dependence of the coercivity of the films has been
also examined, displaying a generic anomalous reentrant behavior at T200 K.
This feature is independent of the substrate orientation and films thickness
and may be associated to the appearance of new pinning centers due to the
nucleation of the -phase at high temperatures.Comment: 9 pages, 7 figure
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
Anisotropic Magnetoresistance in Manganites: Model and Experiment
We present measurements of anisotropic magnetoresistance of
La_{0.75}Sr_{0.25}MnO_3 films deposited on (001) SrTiO_3 substrates, and
develop a model to describe the low temperature AMR in manganites. We measure
an AMR of the order of 10^{-3} for the current I parallel to the [100] axis of
the crystal and vanishing AMR for I//[110], in agreement with the model
predictions.Comment: 4 pages, 4 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
Thermal enhancement of the antiferromagnetic exchange coupling between Fe epilayers separated by a crystalline ZnSe spacer
We have put into evidence the existence of an antiferromagnetic coupling
between iron epilayers separated by a ZnSe crystalline semiconductor. The
effect has been observed for ZnSe spacers thinner than 4 nm at
room-temperature. The coupling constant increases linearly with temperature
with a constant slope of ~5.5x 10-9 J/m2K. The mechanisms that may explain such
exchange interaction are discussed in the manuscript. It results that
thermally-induced effective exchange coupling mediated by spin-dependent on and
off resonant tunnelling of electrons via localized mid-gap defect states in the
ZnSe spacer layer appears to be the most plausible mechanism to induce the
antiferromagnetic coupling.Comment: 29 pages, 8 figure
Magnetic and transport properties of Ag∕Co90Fe10 granular multilayers
We report experimental results on the magnetic and transport properties of Ag/Co 90Fe 10 multilayers with variable Ag and Co 90Fe 10 thicknesses. The magnetism samples was characterized by magnetization measurements and ferromagnetic resonance spectroscopy. These measurements show that the magnetic layers are in general composed by single-domain particles and that the shape and the size of the magnetic clusters can be changed by using an applied magnetic field (H dep) on deposition. The resistivity of these multilayered systems is described by a mixed model that includes current-in-plane and current perpendicular plane transport contributions. The transport model proposed to explain the experimental results emphasizes the role played by the magnetic entities on the scattering processes and strongly depends on the silver layer thickness. An electrical percolative transition is observed for samples grown at H dep>H* dep while the magnetic properties of these samples still show a granularlike behavior. © 2004 American Institute of Physics.Fil:Milano, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Llois, A.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina