10,218 research outputs found
Magnonic spin-transfer torque MRAM with low power, high speed, and error-free switching
A new class of spin-transfer torque magnetic random access memory (STT-MRAM)
is discussed, in which writing is achieved using thermally initiated magnonic
current pulses as an alternative to conventional electric current pulses. The
magnonic pulses are used to destabilize the magnetic free layer from its
initial direction, and are followed immediately by a bipolar electric current
exerting conventional spin-transfer torque on the free layer. The combination
of thermal and electric currents greatly reduces switching errors, and
simultaneously reduces the electric switching current density by more than an
order of magnitude as compared to conventional STT-MRAM. The energy efficiency
of several possible electro-thermal circuit designs have been analyzed
numerically. As compared to STT-MRAM with perpendicular magnetic anisotropy,
magnonic STT-MRAM reduces the overall switching energy by almost 80%.
Furthermore, the lower electric current density allows the use of thicker
tunnel barriers, which should result in higher tunneling magneto-resistance and
improved tunnel barrier reliability. The combination of lower power, improved
reliability, higher integration density, and larger read margin make magnonic
STT-MRAM a promising choice for future non-volatile storage.Comment: 9 Pages, 11 Figure
Critical Binder cumulant for isotropic Ising models on square and triangular lattices
Using Monte Carlo techniques, the critical Binder cumulant U* of isotropic
nearest-neighbour Ising models on square and triangular lattices is studied.
For rectangular shapes, employing periodic boundary conditions, U* is found to
show the same dependence on the aspect ratio for both lattice types. Similarly,
applying free boundary conditions for systems with square as well as circular
shapes for both lattices, the simulational findings are also consistent with
the suggestion that, for isotropic Ising models with short-range interactions,
U* depends on the shape and the boundary condition, but not on the lattice
structure.Comment: 7 pages, 4 figures, submitted to J. Stat. Mec
Thickness dependent magnetotransport in ultra-thin manganite films
To understand the near-interface magnetism in manganites, uniform, ultra-thin
films of La_{0.67}Sr_{0.33}MnO_3 were grown epitaxially on single crystal (001)
LaAlO_3 and (110) NdGaO_3 substrates. The temperature and magnetic field
dependent film resistance is used to probe the film's structural and magnetic
properties. A surface and/or interface related dead-layer is inferred from the
thickness dependent resistance and magnetoresistance. The total thickness of
the dead layer is estimated to be for films on NdGaO_3 and for films on LaAlO_3.Comment: 11 pages, 4 figure
Redshifted 21cm Signatures Around the Highest Redshift Quasars
The Ly-alpha absorption spectrum of the highest redshift quasars indicates
that they are surrounded by giant HII regions, a few Mpc in size. The neutral
gas around these HII regions should emit 21cm radiation in excess of the Cosmic
Microwave Background, and enable future radio telescopes to measure the
transverse extent of these HII regions. At early times, the HII regions expand
with a relativistic speed. Consequently, their measured sizes along the
line-of-sight (via Ly-alpha absorption) and transverse to it (via 21 cm
emission) should have different observed values due to relativistic time-delay.
We show that the combined measurement of these sizes would directly constrain
the neutral fraction of the surrounding intergalactic medium (IGM) as well as
the quasar lifetime. Based on current number counts of luminous quasars at z>6,
an instrument like LOFAR should detect >2 redshifted 21cm shells per field
(with a radius of 11 degrees) around active quasars as bright as those already
discovered by SDSS, and >200 relic shells of inactive quasars per field. We
show that Ly-alpha photons from the quasar are unable to heat the IGM or to
couple the spin and kinetic temperatures of atomic hydrogen beyond the edge of
the HII region. The detection of the IGM in 21cm emission around high redshift
quasars would therefore gauge the presence of a cosmic Ly-alpha background
during the reionization epoch.Comment: 11 pages, 6 figures. Submitted to Ap
Temperature- and Bias-dependence of magnetoresistance in doped manganite thin film trilayer junctions
Thin film trilayer junction of LaSrMnO - SrTiO -
LaSrMnO shows a factor of 9.7 change in resistance, in a
magnetic field around 100 Oe at 14K. The junction magnetoresistance is bias and
temperature dependent. The energy scales associated with bias and temperature
dependence are an order of magnitude apart. The same set of energies also
determine the bias and temperature dependence of the differential conductance
of the junction. We discuss these results in terms of metallic cluster
inclusions at the junction-barrier interface.Comment: 3 pages, 4 figure
Self-forces from generalized Killing fields
A non-perturbative formalism is developed that simplifies the understanding
of self-forces and self-torques acting on extended scalar charges in curved
spacetimes. Laws of motion are locally derived using momenta generated by a set
of generalized Killing fields. Self-interactions that may be interpreted as
arising from the details of a body's internal structure are shown to have very
simple geometric and physical interpretations. Certain modifications to the
usual definition for a center-of-mass are identified that significantly
simplify the motions of charges with strong self-fields. A derivation is also
provided for a generalized form of the Detweiler-Whiting axiom that pointlike
charges should react only to the so-called regular component of their
self-field. Standard results are shown to be recovered for sufficiently small
charge distributions.Comment: 21 page
Topological Modes in Dual Lattice Models
Lattice gauge theory with gauge group is reconsidered in four
dimensions on a simplicial complex . One finds that the dual theory,
formulated on the dual block complex , contains topological modes
which are in correspondence with the cohomology group ,
in addition to the usual dynamical link variables. This is a general phenomenon
in all models with single plaquette based actions; the action of the dual
theory becomes twisted with a field representing the above cohomology class. A
similar observation is made about the dual version of the three dimensional
Ising model. The importance of distinct topological sectors is confirmed
numerically in the two dimensional Ising model where they are parameterized by
.Comment: 10 pages, DIAS 94-3
Energy-momentum balance in quantum dielectrics
We calculate the energy-momentum balance in quantum dielectrics such as
Bose-Einstein condensates. In agreement with the experiment [G. K. Campbell et
al. Phys. Rev. Lett. 94, 170403 (2005)] variations of the Minkowski momentum
are imprinted onto the phase, whereas the Abraham tensor drives the flow of the
dielectric. Our analysis indicates that the Abraham-Minkowski controversy has
its root in the Roentgen interaction of the electromagnetic field in dielectric
media
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