201,879 research outputs found
Invalidation of the Kelvin Force in Ferrofluids
Direct and unambiguous experimental evidence for the magnetic force density
being of the form in a certain geometry - rather than being the
Kelvin force - is provided for the first time. (M is the
magnetization, H the field, and B the flux density.)Comment: 4 pages, 4 figure
scalar glueball in finite-width Gaussian sum rules
Based on a semiclassical expansion for quantum chromodynamics in the
instanton liquid background, the correlation function of the scalar
glueball current is given, and the properties of the scalar glueball
are studied in the framework of Gaussian sum rules. Besides the pure classical
and quantum contributions, the contributions arising from the interactions
between the classical instanton fields and quantum gluons are come into play.
Instead of the usual zero-width approximation for the resonance, the
Breit-Wigner form for the spectral function of the finite-width resonance is
adopted. The family of the Gaussian sum rules for the scalar glueball in
quantum chromodynamics with and without light quarks is studied. A consistency
between the subtracted and unsubtracted sum rules is very well justified, and
the values of the decay width and the coupling to the corresponding current for
the resonance, in which the scalar glueball fraction is dominant, are
obtained.Comment: 18pages, 9figure
Solvent coarse-graining and the string method applied to the hydrophobic collapse of a hydrated chain
Using computer simulations of over 100,000 atoms, the mechanism for the
hydrophobic collapse of an idealized hydrated chain is obtained. This is done
by coarse-graining the atomistic water molecule positions over 129,000
collective variables that represent the water density field and then using the
string method in these variables to compute the minimum free energy pathway
(MFEP) for the collapsing chain. The dynamical relevance of the MFEP (i.e. its
coincidence with the mechanism of collapse) is validated a posteriori using
conventional molecular dynamics trajectories. Analysis of the MFEP provides
atomistic confirmation for the mechanism of hydrophobic collapse proposed by
ten Wolde and Chandler. In particular, it is shown that lengthscale-dependent
hydrophobic dewetting is the rate-limiting step in the hydrophobic collapse of
the considered chain.Comment: 11 pages, 7 figures, including supporting informatio
Electric Control of Spin Currents and Spin-Wave Logic
Spin waves in insulating magnets are ideal carriers for spin currents with
low energy dissipation. An electric field can modify the dispersion of spin
waves, by directly affecting, via spin-orbit coupling, the electrons that
mediate the interaction between magnetic ions. Our microscopic calculations
based on the super-exchange model indicate that this effect of the electric
field is sufficiently large to be used to effectively control spin currents. We
apply these findings to the design of a spin-wave interferometric device, which
acts as a logic inverter and can be used as a building block for
room-temperature, low-dissipation logic circuits.Comment: 4 pages, 3 figures, added the LL equation and the discussion on
spin-wave-induced electric field, accepted by PR
Time-Resolved Magnetic Relaxation of a Nanomagnet on Subnanosecond Time Scales
We present a two-current-pulse temporal correlation experiment to study the
intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during
and following a pulse excitation. This method is applied to a model
spin-transfer system, a spin valve nanopillar with perpendicular magnetic
anisotropy. Two-pulses separated by a short delay (< 500 ps) are shown to lead
to the same switching probability as a single pulse with a duration that
depends on the delay. This demonstrates a remarkable symmetry between magnetic
excitation and relaxation and provides a direct measurement of the magnetic
relaxation time. The results are consistent with a simple finite temperature
Fokker-Planck macrospin model of the dynamics, suggesting more coherent
magnetization dynamics in this short time nonequilibrium limit than near
equilibrium
Frustration Driven Stripe Domain Formation in Co/Pt Multilayer Films
We report microscopic mechanisms for an unusual magnetization reversal
behavior in Co/Pt multilayers where some of the first-order reversal curves
protrude outside of the major loop. Transmission x-ray microscopy reveals a
fragmented stripe domain topography when the magnetic field is reversed prior
to saturation, in contrast to an interconnected pattern when reversing from a
saturated state. The different domain nucleation and propagation behaviors are
due to unannihilated domains from the prior field sweep. These residual domains
contribute to random dipole fields that impede the subsequent domain growth and
prevent domains from growing as closely together as for the interconnected
pattern.Comment: 13 pages, 3 figures, to appear in AP
- …