5,338 research outputs found
The effects of nuclear spins on the quantum relaxation of the magnetization for the molecular nanomagnet Fe_8
The strong influence of nuclear spins on resonant quantum tunneling in the
molecular cluster Fe_8 is demonstrated for the first time by comparing the
relaxation rate of the standard Fe_8 sample with two isotopic modified samples:
(i) 56_Fe is replaced by 57_Fe, and (ii) a fraction of 1_H is replaced by 2_H.
By using a recently developed "hole digging" method, we measured an intrinsic
broadening which is driven by the hyperfine fields. Our measurements are in
good agreement with numerical hyperfine calculations. For T > 1.5 K, the
influence of nuclear spins on the relaxation rate is less important, suggesting
that spin-phonon coupling dominates the relaxation rate at higher temperature.Comment: 4 pages, 5 figure
Transition to Chaotic Phase Synchronization through Random Phase Jumps
Phase synchronization is shown to occur between opposite cells of a ring
consisting of chaotic Lorenz oscillators coupled unidirectionally through
driving. As the coupling strength is diminished, full phase synchronization
cannot be achieved due to random generation of phase jumps. The brownian
dynamics underlying this process is studied in terms of a stochastic diffusion
model of a particle in a one-dimensional medium.Comment: Accepted for publication in IJBC, 10 pages, 5 jpg figure
Casimir energy between media-separated cylinders: the scalar case
We derive exact expressions for the Casimir scalar interaction energy between
media-separated eccentric dielectric cylinders and for the media-separated
cylinder-plane geometry using a mode-summation approach. Similarly to the
electromagnetic Casimir-Lifshitz interaction energy between fluid-separated
planar plates, the force between cylinders is attractive or repulsive depending
on the relative values of the permittivities of the three intervening media.Comment: New figure and discussion about the integration contour in the
complex plan
Low-temperature specific heat of real crystals: Possibility of leading contribution of optical and short-wavelength acoustical vibrations
We point out that the repeatedly reported glass-like properties of
crystalline materials are not necessarily associated with localized (or
quasilocalized) excitations. In real crystals, optical and short-wavelength
acoustical vibrations remain damped due to defects down to zero temperature. If
such a damping is frequency-independent, e.g. due to planar defects or charged
defects, these optical and short-wavelength acoustical vibrations yield a
linear-in- contribution to the low-temperature specific heat of the crystal
lattices. At low enough temperatures such a contribution will prevail over that
of the long-wavelength acoustical vibrations (Debye contribution). The
crossover between the linear and the Debye regime takes place at , where is the concentration of the defects responsible for the
damping. Estimates show that this crossover could be observable.Comment: 5 pages. v4: Error in Appendix corrected, which does not change the
main results of the pape
Empirical constraints on the origin of fast radio bursts: volumetric rates and host galaxy demographics as a test of millisecond magnetar connection
The localization of the repeating FRB 121102 to a low-metallicity dwarf
galaxy at , and its association with a quiescent radio source,
suggests the possibility that FRBs originate from magnetars, formed by the
unusual supernovae in such galaxies. We investigate this via a comparison of
magnetar birth rates, the FRB volumetric rate, and host galaxy demographics. We
calculate average volumetric rates of possible millisecond magnetar production
channels such as superluminous supernovae (SLSNe), long and short gamma-ray
bursts (GRBs), and general magnetar production via core-collapse supernovae.
For each channel we also explore the expected host galaxy demographics using
their known properties. We determine for the first time the number density of
FRB emitters (the product of their volumetric birthrate and lifetime), Gpc, assuming that FRBs are predominantly emitted
from repetitive sources similar to FRB 121102 and adopting a beaming factor of
0.1. By comparing rates we find that production via rare channels (SLSNe, GRBs)
implies a typical FRB lifetime of 30-300 yr, in good agreement with
other lines of argument. The total energy emitted over this time is consistent
with the available energy stored in the magnetic field. On the other hand, any
relation to magnetars produced via normal core-collapse supernovae leads to a
very short lifetime of 0.5yr, in conflict with both theory and
observation. We demonstrate that due to the diverse host galaxy distributions
of the different progenitor channels, many possible sources of FRB birth can be
ruled out with host galaxy identifications. Conversely, targeted
searches of galaxies that have previously hosted decades-old SLSNe and GRBs may
be a fruitful strategy for discovering new FRBs and related quiescent radio
sources, and determining the nature of their progenitors
Electron interaction with domain walls in antiferromagnetically coupled multilayers
For antiferromagnetically coupled Fe/Cr multilayers the low field
contribution to the resistivity, which is caused by the domain walls, is
strongly enhanced at low temperatures. The low temperature resistivity varies
according to a power law with the exponent about 0.7 to 1. This behavior can
not be explained assuming ballistic electron transport through the domain
walls. It is necessary to invoke the suppression of anti-localization effects
(positive quantum correction to conductivity) by the nonuniform gauge fields
caused by the domain walls.Comment: 5 pages with 3 figure
Structure and magnetic properties of FeNi/Ti sputtered multilayers
The microstructure, anisotropic magnetoresistance, magnetic properties and magnetic domain structure of sputtered FeNi films and [Ti/FeNi]n (n = 2-16) multilayers were comparatively analyzed. It was found that although the grain size increases with an increase of the FeNi thickness both in the case of FeNi films and [Ti/FeNi]n multilayers, it did not exceed 25 nm. The values of anisotropic magnetoresistance for FeNi films and [Ti/FeNi]n multilayers were close to each other showing a weak dependence on the total thickness of the multilayered structure. Coercivity for multilayers was found to be smaller than the coercivity of single layer FeNi films. Despite the absence of a direct exchange interaction between FeNi neighboring layers in the [Ti/FeNi]n structures, their domain structures were found to be quite different from magnetic domains in single layer films due to stray field compensation in the multilayers. Obtained results are useful for the development of sensitive elements for small magnetic field detectors and planar inductors. © 2013 Owned by the authors, published by EDP Sciences
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