4,032 research outputs found
Current-induced metallic behavior in PrCaMnO thin films: competition between Joule heating and nonlinear conduction mechanism
Thin films of Pr0.5Ca0.5MnO3 manganites exhibiting charge/orbital-ordered
properties with colossal magnetoresistance have been synthesized by the pulsed
laser deposition technique on both (100)-SrTiO3 and (100)-LaAlO3 substrates.
The effects of current-induced metallic-behavior of the films are investigated
as a function of the temperature and the magnetic field. Calculations based on
a heat transfer model across the substrate, and our resistivity measurements
reveal effects of Joule heating on charge transport over certain ranges of
temperatures and magnetic fields. Our results also indicate that a nonlinear
conduction, which cannot be explained by homogeneous Joule heating of the film,
is observed when the material is less resistive (10-2 W.cm). The origin of this
behavior is explained with a model based on local thermal instabilities
associated with phase-separation mechanism and a change in the long range
charge-ordered state.Comment: To be published in Phys. Rev.
Magnetocapacitance effect in perovskite-superlattice based multiferroics
We report the structural and magnetoelectrical properties of
LaCaMnO/BaTiO perovskite superlattices grown on
(001)-oriented SrTiO by the pulsed laser deposition technique. Magnetic
hysteresis loops together with temperature dependent magnetic properties
exhibit well-defined coercivity and magnetic transition temperature (T)
\symbol{126}140 K. electrical studies of films show that the
magnetoresistance (MR) is dependent on the BaTiO thickness and negative
as high as 30% at 100K are observed. The electrical studies reveal
that the impedance and capacitance in these films vary with the applied
magnetic field due to the magnetoelectrical coupling in these structures - a
key feature of multiferroics. A negative magnetocapacitance value in the film
as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for
designing novel functional materials.Comment: To be published in Applied Physics Letter
Current-driven magnetization decrease in single crystalline ferromagnetic manganese oxide
The electrical and magnetic response to a bias current has been investigated
in a singlecrystalline ferromagnetic manganese oxide
CaMnO . A significant decrease of the magnetization is
observed at the same threshold current where a non-linearity of V-I
characteristics appears. Such a behavior cannot be understood in the framework
of the filamentary picture usually invoked for the non linearity of the other
manganese oxides. Instead, an analogy with spintronic features might be useful
and experimental signatures seem to be in agreement with excitations of spin
waves by an electric current. This provides an example of a bulk system in
which the spin polarized current induces a macroscopic change in the
magnetization.Comment: 3 pages, 4 figure
Curie Point Pyrolysis Gas Chromatography
In Curie Point pyrolysis gas chromatography a ferromagnetic conductor in contact with the sample is heated inside a low volume glass capillary which is inserted into an rf coil with the carrier gas flowing through the capillary. The intrinsic properties of the conductor permit a self-control of the temperature to the Curie Point. The optimum wire diameter for a rapid warm-up is a function of the rf frequency. In order to have a fast temperature drop after cutting the rf field, small wire diameters are preferable. For such conductors relatively high frequencies are inherently necessary for a fast stabilization to the Curie Point. So far no differences in the self-controlled end-temperatures have been detected for wires of different origi
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
The influence of twin boundaries on the Flux Line Lattice structure in YBaCuO: a study by Small Angle Neutron Scattering
The influence of Twin Boundaries (TB) on the Flux Line Lattice(FLL) structure
was investigated by Small Angle Neutron Scattering (SANS). YBaCuO single
crystals possessing different TB densities were studied. The SANS experiments
show that the TB strongly modify the structure of the FLL. The flux lines
meander as soon as the magnetic field makes an angle with the TB direction.
According to the value of this angle but also to the ratio of the flux lines
density over the TB density, one observes that the FLL exhibits two different
unit cells in the plane perpendicular to the magnetic field. One is the
classical hexagonal and anisotropic cell while the other is affected by an
additional deformation induced by the TB. We discuss a possible relation
between this deformation and the increase of the critical current usually
observed in heavily twinned samples.Comment: accepted for publication in Phys Rev
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