10,878 research outputs found
Ferromagnetism in nanoscale BiFeO3
A remarkably high saturation magnetization of ~0.4mu_B/Fe along with room
temperature ferromagnetic hysteresis loop has been observed in nanoscale (4-40
nm) multiferroic BiFeO_3 which in bulk form exhibits weak magnetization
(~0.02mu_B/Fe) and an antiferromagnetic order. The magnetic hysteresis loops,
however, exhibit exchange bias as well as vertical asymmetry which could be
because of spin pinning at the boundaries between ferromagnetic and
antiferromagnetic domains. Interestingly, like in bulk BiFeO_3, both the
calorimetric and dielectric permittivity data in nanoscale BiFeO_3 exhibit
characteristic features at the magnetic transition point. These features
establish formation of a true ferromagnetic-ferroelectric system with a
coupling between the respective order parameters in nanoscale BiFeO_3.Comment: 13 pages including 4 figures; pdf only; submitted to Appl. Phys. Let
Unitarity constraints on the stabilized Randall-Sundrum scenario
Recently proposed stabilization mechanism of the Randall-Sundrum metric gives
rise to a scalar radion, which couples universally to matter with a weak
interaction ( TeV) scale. Demanding that gauge boson scattering as
described by the effective low enerrgy theory be unitary upto a given scale
leads to significant constraints on the mass of such a radion.Comment: 10 page Latex 2e file including 4 postscript figures. Accepted in
Journal of Physics
Ion-acoustic solitons in warm magnetoplasmas with super-thermal electrons
In this work, the phenomenon of formation of localised electrostatic waves
(ESW) or soliton is considered in a warm magnetoplasma with the possibility of
non-thermal electron distribution. The parameter regime considered here is
relevant in case of magnetospheric plasmas. We show that deviation from a usual
relaxed Maxwellian distribution of the electron population has a significant
bearing in the allowed parameter regime, where these ESWs can be found. We
further consider the presence of more than one electron temperature, which is
inspired by recent space-based observations[key-2].Comment: 10 pages, 5 figure
Silicon materials task of the low cost solar array project, part 2
Purity requirements for solar cell grade silicon material was developed and defined by evaluating the effects of specific impurities and impurity levels on the performance of silicon solar cells. Also, data was generated forming the basis for cost-tradeoff analyses of silicon solar cell material. Growth, evaluation, solar cell fabrication and testing was completed for the baseline boron-doped Czochralski material. Measurements indicate Cn and Mn seriously degrade cell performance, while neither Ni nor Cu produce any serious reduction in cell efficiency
Silicon materials task of the low cost solar array project. Phase 3: Effect of impurities and processing on silicon solar cells
The 13th quarterly report of a study entitled an Investigation of the Effects of Impurities and Processing on Silicon Solar Cells is given. The objective of the program is to define the effects of impurities, various thermochemical processes and any impurity-process interactions on the performance of terrestrial silicon solar cells. The Phase 3 program effort falls in five areas: (1) cell processing studies; (2) completion of the data base and impurity-performance modeling for n-base cells; (3) extension of p-base studies to include contaminants likely to be introduced during silicon production, refining or crystal growth; (4) anisotropy effects; and (5) a preliminary study of the permanence of impurity effects in silicon solar cells. The quarterly activities for this report focus on tasks (1), (3) and (4)
Silicon dendritic web material
The development of a low cost and reliable contact system for solar cells and the fabrication of several solar cell modules using ultrasonic bonding for the interconnection of cells and ethylene vinyl acetate as the potting material for module encapsulation are examined. The cells in the modules were made from dendritic web silicon. To reduce cost, the electroplated layer of silver was replaced with an electroplated layer of copper. The modules that were fabricated used the evaporated Ti, Pd, Ag and electroplated Cu (TiPdAg/Cu) system. Adherence of Ni to Si is improved if a nickel silicide can be formed by heat treatment. The effectiveness of Ni as a diffusion barrier to Cu and the ease with which nickel silicide is formed is discussed. The fabrication of three modules using dendritic web silicon and employing ultrasonic bonding for interconnecting calls and ethylene vinyl acetate as the potting material is examined
Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4
Using density-functional theory calculations and experimental investigations
on structural, magnetic and dielectric properties, we have elucidated a unique
tetragonal ground state for MnTi2O4, a Ti^{3+} (3d^1)-ion containing
spinel-oxide. With lowering of temperature around 164 K, cubic MnTi2O4
undergoes a structural transition into a polar P4_1 tetragonal structure and at
further lower temperatures, around 45 K, the system undergoes a paramagnetic to
ferrimagnetic transition. Magnetic superexchange interactions involving Mn and
Ti spins and minimization of strain energy associated with co-operative
Jahn-Teller distortions plays a critical role in stabilization of the unique
tetramer-orbital ordered ground state which further gives rise to lattice
chirality through subtle Ti-Ti bond-length modulations
Comments on scalar-tensor representation of nonlocally corrected gravity
The scalar-tensor representation of nonlocally corrected gravity is
considered. Some special solutions of the vacuum background equations were
obtained that indicate to the nonequivalence of the initial theory and its
scalar-tensor representation.Comment: 6 pages, refs adde
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