1,321 research outputs found
Micromagnetic simulations of the magnetization precession induced by a spin polarized current in a point contact geometry
This paper is devoted to numerical simulations of the magnetization dynamics
driven by a spin-polarized current in extended ferromagnetic multilayers when a
point-contact setup is used. We present (i) detailed analysis of methodological
problems arising by such simulations and (ii) physical results obtained on a
system similar to that studied in Rippard et al., Phys. Rev. Lett., v. 92,
027201 (2004). We demonstrate that the usage of a standard Slonczewski
formalism for the phenomenological treatment of a spin-induced torque leads to
a qualitative disagreement between simulation results and experimental
observations and discuss possible reasons for this discrepancy.Comment: Invited paper on MMM2005 (San Jose); accepted for publication in J.
Applied Physic
Magnetization precession due to a spin polarized current in a thin nanoelement: numerical simulation study
In this paper a detailed numerical study (in frames of the Slonczewski
formalism) of magnetization oscillations driven by a spin-polarized current
through a thin elliptical nanoelement is presented. We show that a
sophisticated micromagnetic model, where a polycrystalline structure of a
nanoelement is taken into account, can explain qualitatively all most important
features of the magnetization oscillation spectra recently observed
experimentally (S.I. Kiselev et al., Nature, vol. 425, p. 380 (2003), namely:
existence of several equidistant spectral bands, sharp onset and abrupt
disappearance of magnetization oscillations with increasing current, absence of
the out-of-plane regime predicted by a macrospin model and the relation between
frequencies of so called small-angle and quasichaotic oscillations. However, a
quantitative agreement with experimental results (especially concerning the
frequency of quasichaotic oscillations) could not be achieved in the region of
reasonable parameter values, indicating that further model refinement is
necessary for a complete understanding of the spin-driven magnetization
precession even in this relatively simple experimental situation.Comment: Submitted to Phys. Rev. B; In this revised version figure positions
on the page have been changed to ensure correct placements of the figure
caption
Magnetodipolar interlayer interaction effect on the magnetization dynamics of a trilayer square element with the Landau domain structure
We present a detailed numerical simulation study of the effects caused by the magnetodipolar interaction between ferromagnetic ͑FM͒ layers of a trilayer magnetic nanoelement on its magnetization dynamics. As an example, we use a Co/ Cu/ Ni 80 Fe 20 element with a square lateral shape where the magnetization of FM layers forms a closed Landau-like domain pattern. First, we show that when the thickness of the nonmagnetic ͑NM͒ spacer is in the technology relevant region h ϳ 10 nm, magnetodipolar interaction between 90°Neel domain walls in FM layers qualitatively changes the equilibrium magnetization state of these layers. In the main part of the paper, we compare the magnetization dynamics induced by a sub-nsec field pulse in a single-layer Ni 80 Fe 20 ͑Py͒ element and in the Co/ Cu/ Py trilayer element. Here, we show that ͑i͒ due to the spontaneous symmetry breaking of the Landau state in the FM/NM/FM trilayer, its domains and domain walls oscillate with different frequencies and have different spatial oscillation patterns; ͑ii͒ magnetization oscillations of the trilayer domains are strongly suppressed due to different oscillation frequencies of domains in Co and Py; ͑iii͒ magnetization dynamics qualitatively depends on the relative rotation sense of magnetization states in Co and Py layers and on the magnetocrystalline anisotropy kind of Co crystallites. Finally, we discuss the relation of our findings with experimental observations of magnetization dynamics in magnetic trilayers, performed using the element-specific time-resolved x-ray microscopy
Информационная технология оценки показателей качества жизни пациентов
Оценка качества жизни пациентов на основе многомерного анализа данных (результатов психологического тестирования). Выбор R в качестве основного инструментария.Assessment of the quality of life of patients on the basis of multidimensional data analysis (the results of psychological testing). The choice of R as the main tool
Spin-torque driven magnetization dynamics in a nanocontact setup for low external fields: numerical simulation study
We present numerical simulation studies of the steady-state magnetization
dynamics driven by a spin-polarized current in a point contact geometry for the
case of a relatively large contact diameter (D = 80 nm) and small external
field (H = 30 Oe). We show, that under these conditions the magnetization
dynamics is qualitatively different from the dynamics observed for small
contacts in large external fields. In particular, the 'bullet' mode with a
homogeneous mode core, which was the dominating localized mode for small
contacts, is not found here. Instead, all localized oscillation modes observed
in simulations correspond to different motion kinds of vortex-antivortex (V-AV)
pairs. These kinds include rotational and translational motion of pairs with
the V-AV distance d ~ D and creation/annihilation of much smaller (satellite)
V-AV pairs. We also show that for the geometry studied here the Oersted field
has a qualitative effect on the magnetization dynamics of a 'free' layer. This
effect offers a possibility to control magnetization dynamics by a suitable
electric contact setup, optimized to produce a desired Oersted field. Finally,
we demonstrate that when the magnetization dynamics of the 'fixed' layer
(induced only by the stray field interaction with the 'free' layer) is taken
into account, the threshold current for the oscillation onset is drastically
reduced and new types of localized modes appear. In conclusion, we show that
our simulations reproduce semiquantitatively several important features of the
magnetization dynamics in a point contact system for low external fields
reported experimentally.Comment: 26 pages, 12 figures, submitted to Phys. Rev.
Magnonic Metamaterials
A large proportion of the recent growth of the volume of electromagnetics research has been associated with the emergence of so called electromagnetic metamaterials1 and the discovered ability to design their unusual properties by tweaking the geometry and structure of the constituent “meta-atoms”. For example, negative permittivity and negative
permeability can be achieved, leading to negative refractive index metamaterials. The negative permeability could be obtained via geometrical control of high frequency currents, e.g. in arrays of split ring resonators, or alternatively one could rely on spin resonances in
natural magnetic materials, as was suggested by Veselago. The age of
nanotechnology therefore sets an intriguing quest for additional benefits to be gained by structuring natural magnetic materials into so called magnonic metamaterials, in which the frequency and strength of resonances based on spin waves (magnons) are determined by
the geometry and magnetization configuration of meta-atoms. Spin waves can have frequencies of up to hundreds of GHz (in the exchange dominated regime) and have already been shown to play an important role in the high frequency magnetic response of composites. Moreover, in view of the rapid advances in the field of magnonics, which in particular promises devices employing propagating spin waves, the appropriate
design of magnonic metamaterials with properties defined with respect to propagating spin waves rather than electromagnetic waves acquires an independent and significant importance
Search for charginos in e+e- interactions at sqrt(s) = 189 GeV
An update of the searches for charginos and gravitinos is presented, based on
a data sample corresponding to the 158 pb^{-1} recorded by the DELPHI detector
in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was
found. The lower mass limits are 4-5 GeV/c^2 higher than those obtained at a
centre-of-mass energy of 183 GeV. The (\mu,M_2) MSSM domain excluded by
combining the chargino searches with neutralino searches at the Z resonance
implies a limit on the mass of the lightest neutralino which, for a heavy
sneutrino, is constrained to be above 31.0 GeV/c^2 for tan(beta) \geq 1.Comment: 22 pages, 8 figure
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
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