3,185 research outputs found
Shock wave velocity and shock pressure for low density powders: A novel approach
A novel approach is presented to predict the shock wave velocity as well as the shock wave pressure in powder materials. It is shown that the influence of the specific volume behind the shock wave on shock wave velocity and shock pressure decreases with decreasing initial powder density. The new model is compared with experimental data of various materials: Fe, Cu, Al, C, UO2, Ce2O3, SiO2 (quartz), NaCl, and polystyrene. It is concluded that the model holds in particular for initial powder densities less than 50% and for flyer plate velocities up to 5 km/s.
Direct determination of the step-edge formation energies of the energetically stable and unstable double-layer step edges of Si(001)
Scanning tunneling microscopy images of 4.5° misoriented double B stepped Si(001) have been analyzed to determine the double-layer step-edge formation energies of the energetically stable double step (B-type) as well as the energetically unstable double step (A-type). The ordering of the various single- and double-layer step-edge formation energies is in accordance with semiempirical tight-binding-based total-energy calculations performed by Chadi [Phys. Rev. Lett. 59, 1691 (1987)]. Finally, the miscut angle at which the transition between the single- and double-layer stepped surface occurs as calculated using the experimentally obtained step-edge formation energies is in agreement with the experiment
Erratum: Anomalous strong repulsive step-step interaction on slightly misoriented Si(113) [Phys. Rev. B 55, 7864 (1997)]
Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films
Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.Comment: 9 pages, 6 figure
Steering effect on the shape of islands for homoepitaxial growth of Cu on Cu(100)
The steering effect on the growth of islands is investigated by combining
molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. Dynamics of
depositing atoms and kinetics of atoms on a substrate are realized by MD and
KMC, respectively. The reported experimental results on the asymmetric island
growth [van Dijken {\it et al.}, Phys. Rev. Lett. {\bf 82}, 4038 (1999).] is
well reproduced. A salient phenomenon, the reversal of the asymmetry, is found
as the island size increases, and attributed to the asymmetric flux on the
lower terrace of island.Comment: 5 figur
Spin transfer torque oscillator based on asymmetric magnetic tunnel junctions
We present a study of the spin transfer torque oscillator based on
CoFeB/MgO/CoFeB asymmetric magnetic tunnel junctions. We observe microwave
precession in junctions with different thickness of the free magnetization
layer. Taking advantage of the ferromagnetic interlayer exchange coupling
between the free and reference layer in the MTJ and perpendicular interface
anisotropy in thin CoFeB electrode we demonstrate the nanometer scale device
that can generate high frequency signal without external magnetic field
applied. The amplitude of the oscillation exceeds 10 nV/Hz^0.5 at 1.5 GHz.Comment: 4 pages, 4 figures, to be submitted to Applied Physics Letter
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