314 research outputs found
Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography
A combined bottom-up assembly of electrodeposited nanowires and electron beam
lithography technique has been developed to investigate the spin transfer
torque and microwave emission on specially designed nanowires containing a
single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at
zero magnetic field. Interestingly, high frequency vs. magnetic field
tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the
orientation of the applied magnetic field relative to the magnetic layers of
the pseudo spin valve. The frequency values and the emitted signal frequency as
a function of the external magnetic field are in good quantitative agreement
with the analytical vortex model as well as with micromagnetic simulations.Comment: 9 pages, 4 figure
Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes
The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150
nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are
investigated. The comparison of the nanoscopic magnetic force microscopy (MFM)
imaging and the macroscopic behavior as measured by alternating gradient force
magnetometry (AGFM) is made. It is shown that MFM is a complementary technique
that provides an understanding of the magnetization reversal characteristics at
the microscopic scale of individual nanostructures. The local hysteresis loops
have been extracted by MFM measurements. The influence of the shape of such
elongated nanostructures on the dipolar coupling and consequently on the
squareness of the hysteresis curves is demonstrated. It is shown that the
nanowires exhibit stronger magnetic interactions than nanotubes. The
non-uniformity of the magnetization states is also revealed by combining the
MFM and AGFM measurements.Comment: 7 pages, 5 figure
Time-domain numerical simulations of multiple scattering to extract elastic effective wavenumbers
Elastic wave propagation is studied in a heterogeneous 2-D medium consisting
of an elastic matrix containing randomly distributed circular elastic
inclusions. The aim of this study is to determine the effective wavenumbers
when the incident wavelength is similar to the radius of the inclusions. A
purely numerical methodology is presented, with which the limitations usually
associated with low scatterer concentrations can be avoided. The elastodynamic
equations are integrated by a fourth-order time-domain numerical scheme. An
immersed interface method is used to accurately discretize the interfaces on a
Cartesian grid. The effective field is extracted from the simulated data, and
signal-processing tools are used to obtain the complex effective wavenumbers.
The numerical reference solution thus-obtained can be used to check the
validity of multiple scattering analytical models. The method is applied to the
case of concrete. A parametric study is performed on longitudinal and
transverse incident plane waves at various scatterers concentrations. The phase
velocities and attenuations determined numerically are compared with
predictions obtained with multiple scattering models, such as the Independent
Scattering Approximation model, the Waterman-Truell model, and the more recent
Conoir-Norris model.Comment: Waves in Random and Complex Media (2012) XX
Effects of nonzero photon momentum in (\gamma,2e) processes
We study the effects of nonzero photon momentum on the triply-differential
cross section for (\gamma,2e) processes. Due to the low value of the photon
momentum, these effects are weak and manifest only in special kinematical
conditions like the back-to-back emission of the electrons with equal energy
sharing. Helium and a few light helium-like ions are treated in detail. Quite
unexpectedly, the magnitude of these effects is maximal for relatively small
photon energies. However, although this effect on the TDCS remains rather
small, of the order of a few mbarn eV^{-1} sr^{-2}, it is sufficient to be
observed experimentally.Comment: 8 pages, 7 figures, 1 tabl
Static field limit of excitation probabilities in laser-atom interactions
We consider the interaction of atomic hydrogen, in its ground state, with an electromagnetic pulse whose duration is fixed in terms of the number of optical cycles. We study the probability of excitation of the atom in the static field limit i.e. for field frequencies going to zero. Despite the fact that the well-known Born–Fock adiabatic theorem is valid only for a system whose energy spectrum is discrete, we show that it is still possible to use this theorem to derive, in the low frequency limit, an analytical formula which gives the probability of transition to any excited state of the atom as a function of the field intensity, the carrier envelope phase and the number of optical cycles within the pulse. The results for the probability of excitation to lowlying excited states, obtained with this formula, agree with those we get by solving the timedependent Schrödinger equation. The domain of validity is discussed in detail
Magnetic force microscopy study of the switching field distribution of low density arrays of single domain magnetic nanowires
In the present work, we report on the in situ magnetic force microscopy (MFM)
study of the magnetization reversal in two-dimensional arrays of ferromagnetic
Ni80Fe20 and Co55Fe45 nanowires(NW) with different diameters (40, 50, 70 and
100 nm) deposited inside low porosity (P<1%) nanoporous polycarbonate
membranes. In such arrays, the nanowires are sufficiently isolated from each
other so that long range dipolar interactions can be neglected. The MFM
experiments performed for different magnetization states at the same spot of
the samples are analysed to determine the switching field distribution (SFD).
The magnetization curves obtained from the MFM images are relatively square
shaped. The SFD widths are narrower compared to those obtained for high density
arrays. The weak broadening of the curves may be ascribed to the NW intrinsic
SFD. The influence of diameter and composition of the ferromagnetic NW is also
investigated.Comment: 6 pages, 4 figures, To appear in Journal of Applied Physic
Decay versus survival of a localized state subjected to harmonic forcing: exact results
We investigate the survival probability of a localized 1-d quantum particle
subjected to a time dependent potential of the form with
or . The particle is
initially in a bound state produced by the binding potential . We
prove that this probability goes to zero as for almost all values
of , , and . The decay is initially exponential followed by a
law if is not close to resonances and is small; otherwise
the exponential disappears and Fermi's golden rule fails. For exceptional sets
of parameters and the survival probability never decays to zero,
corresponding to the Floquet operator having a bound state. We show similar
behavior even in the absence of a binding potential: permitting a free particle
to be trapped by harmonically oscillating delta function potential
Magnetic Behavior of Co/Pt and TbCo Nanocaps Assembly for Bit Pattern Media
Large area patterning of self-assembled alumina nanobumps, with hexagonally close-packed order, has
been used to create ordered array of bit pattern magnetic media. We have studied the magnetic properties
of perpendicular magnetic TbCo alloy and Co/Pt multilayers deposited on self assembled alumina
nanobumps. Measurement of reversal field as a function of field intensity, as well as magnetic force
microscopy images confirm the weakness of exchange coupling between bits in the case of Co/Pt multilayer
while stronger coupling is observed in the case of TbCo alloys.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3535
- …