33,733 research outputs found
Microscopic observations of X-ray and gamma-ray induced decomposition of ammonium perchlorate crystals
The X-ray and gamma-ray induced decomposition of ammonium perchlorate was studied by optical, transmission, and scanning electron microscopy. This material is a commonly used oxidizer in solid propellents which could be employed in deep-space probes, and where they will be subjected to a variety of radiations for as long as ten years. In some respects the radiation-induced damage closely resembles the effects produced by thermal decomposition, but in other respects the results differ markedly. Similar radiation and thermal effects include the following: (1) irregular or ill-defined circular etch pits are formed in both cases; (2) approximately the same size pits are produced; (3) the pit density is similar; (4) the c face is considerably more reactive than the m face; and (5) most importantly, many of the etch pits are aligned in crystallographic directions which are the same for thermal or radiolytic decomposition. Thus, dislocations play an important role in the radiolytic decomposition process
Different steady states for spin currents in noncollinear multilayers
We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.Comment: 8 pages, no figure. Accepted for publication in Journal of Physics:
Condensed Matte
The electrical current effect in phase separated La5/8-yPryCa3/8MnO3: Charge order melting vs. Joule heating
We have studied the effect of electric field on transport properties of the
prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our
results show that the suggested image in which the charge ordered state is
melted by the appliance of an electric current and/or voltage has to be
revised. We were able to explain the observed resistivity drop in terms of an
artifact related to Joule heating and the particular hysteresis that the system
under study display, common to many other phase separated manganites.Comment: 2 figures. Accepted in J. Appl. Phy
Microscopic theory of Cooper pair beam splitters based on carbon nanotubes
We analyze microscopically a Cooper pair splitting device in which a central
superconducting lead is connected to two weakly coupled normal leads through a
carbon nanotube. We determine the splitting efficiency at resonance in terms of
geometrical and material parameters, including the effect of spin-orbit
scattering. While the efficiency in the linear regime is limited to 50% and
decay exponentially as a function of the width of the superconducting region we
show that it can rise up to in the non-linear regime for certain
regions of the stability diagram.Comment: 5 pages, 5 figure
Correlation between magnetic and transport properties of phase separated LaCaMnO
The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
LaCaMnO is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.Comment: 3 pages, 3 figures, presented at the Fifth LAW-MMM, to appear in
Physica B, Minor change
PFM Simulator
Pulse frequency modulation simulator for design and testing of telemetry equipment for satellite system
Magnetoresistive memory in phase separated LaCaMnO
We have studied a non volatile memory effect in the mixed valent compound
LaCaMnO induced by magnetic field (H). In a previous work
[R.S. Freitas et al., Phys. Rev. B 65 (2002) 104403], it has been shown that
the response of this system upon application of H strongly depends on the
temperature range, related to three well differentiated regimes of phase
separation occurring below 220 K. In this work we compare memory capabilities
of the compound, determined following two different experimental procedures for
applying H, namely zero field cooling and field cooling the sample. These
results are analyzed and discussed within the scenario of phase separation.Comment: 4 pages, 2 figure
The steady state in noncollinear magnetic multilayers
There are at least two different putative steady state solutions for current
across noncollinear magnetic multilayers; one has a discontinuity in the spin
current at the interface the other is continuous. We compare the resistance of
the two and find the solution with the continuous spin currents is lower. By
using the entropic principle we can state that this solution is a better
estimate of the resistance for a noncollinear magneticComment: 14 pages, 4 figures,Submitted to Physical Review
Lateral diffusive spin transport in layered structures
A one dimensional theory of lateral spin-polarized transport is derived from
the two dimensional flow in the vertical cross section of a stack of
ferromagnetic and paramagnetic layers. This takes into account the influence of
the lead on the lateral current underneath, in contrast to the conventional 1D
modeling by the collinear configuration of lead/channel/lead. Our theory is
convenient and appropriate for the current in plane configuration of an
all-metallic spintronics structure as well as for the planar structure of a
semiconductor with ferromagnetic contacts. For both systems we predict the
optimal contact width for maximal magnetoresistance and propose an electrical
measurement of the spin diffusion length for a wide range of materials.Comment: 4 pages, 3 figure
- …