共查询到20条相似文献,搜索用时 31 毫秒
1.
Spin-transfer induced ultrafast precessional switching of magnetization in a Co/Cu/Co nanopillar device is studied. Micromagnetic calculations show that precessional magnetization switching occurs above a threshold current. The presence of interface uniaxial anisotropy in the Co-thin film free layer influences heavily the current and the energy required to initiate the switching in the device, and the speed of the precessional switching. The threshold current and the precessional switching time are significantly reduced by this effect. 相似文献
2.
A new way of magnetization switching employing both the spin-transfer torque and the torque by a magnetic field is proposed. The solution of the Landau–Lifshitz–Gilbert equation shows that the dynamics of the magnetization in the initial stage of the switching is similar to that in the precessional switching, while that in the final stage is rather similar to the relaxing switching. We call the present method the relaxing-precessional switching. It offers a faster and lower-power-consuming way of switching than the relaxing switching and a more controllable way than the precessional switching. 相似文献
3.
The special features of precessional motion under ferromagnetic resonance conditions with perpen-dicular magnetization of the film are investigated on the basis of a numerical solution of the equations of motion of magnetization in a (111) type iron garnet film. Several nonlinear magnetization precession regimes exist for fixed values of the crystallographic and induced anisotropies. Depending on the value of the magnetizing field and the amplitude of the microwave field, precession occurs around the normal to the film with the third harmonic of the fundamental frequency making a small or large contribution to the nutation motion and with a small or large amplitude of the precession angle. Precession regimes around one of three symmetric directions different from the direction of the normal are possible. Narrow ranges of the static field, where dynamical bistability and regimes with a period which is a multiple of the period of the microwave field are realized, exist. 相似文献
4.
We study how a magnetic field step triggers the precessional switching of the magnetization in an isotropic thin film. Using a variational approach, we make an analytical estimate of the switching frequency. We compare it to more general analytical models, and to the results obtained numerically by direct integration of the equations of motion. We show that the periodic motions of the three magnetization components can be described satisfactorily with truncated Fourier expansions, indicating a relatively high spectral purity of the magnetic response. Our analytical expressions are simple enough to be physically transparent at first sight, in contrast to the results of the more elaborate models that treat also anisotropy. 相似文献
5.
HUANG HouBing MA XingQiao YUE Tao XIAO ZhiHua SHI SanQiang & CHEN LongQing 《中国科学:物理学 力学 天文学(英文版)》2011,(7)
The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ... 相似文献
6.
Serrano-Guisan S Rott K Reiss G Langer J Ocker B Schumacher HW 《Physical review letters》2008,101(8):087201
We explore the ultrafast limit of spin torque magnetization reversal time. Spin torque precession during a spin torque current pulse and free magnetization ringing after the pulse is detected by time-resolved magnetotransport. Adapting the duration of the pulse to the precession period allows coherent control of the final orientation of the magnetization. In the presence of a hard axis bias field, we find optimum quasiballistic spin torque magnetization reversal by a single precessional turn directly from the initial to the reversed equilibrium state. 相似文献
7.
We study analytically the precessional switching of the magnetization of a thin macrospin. We analyze its response when subjected to an external field along its in-plane hard axis. We derive the exact trajectories of the magnetization. The switching versus non switching behavior is delimited by a bifurcation trajectory, for applied fields equal to half of the effective anisotropy field. A magnetization going through this bifurcation trajectory passes exactly along the hard axis and exhibits a vanishing characteristic frequency at that unstable point, which makes the trajectory noise sensitive. Attempting to approach the related minimal cost in applied field makes the magnetization final state unpredictable. We add finite damping in the model as a perturbative, energy dissipation factor. For a large applied field, the system switches several times back and forth. Several trajectories can be gone through before the system has dissipated enough energy to converge to one attracting equilibrium state. For some moderate fields, the system switches only once by a relaxation dominated precessional switching. We show that the associated switching field increases linearly with the damping parameter. The slope scales with the square root of the effective anisotropy. Our simple concluding expressions are useful to assess the potential application of precessional switching in magnetic random access memories.Received: 2 October 2003, Published online: 19 November 2003PACS:
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.) - 75.60.Jk Magnetization reversal mechanisms - 75.75. + a Magnetic properties of nanostructures 相似文献
8.
9.
Schumacher HW Chappert C Crozat P Sousa RC Freitas PP Miltat J Fassbender J Hillebrands B 《Physical review letters》2003,90(1):017201
We evidence multiple coherent precessional magnetization reversal in microscopic spin valves. Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ. At high fields a phase coherent reversal is found revealing periodic transitions from switching to nonswitching under variation of pulse parameters. At the low field limit the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold. 相似文献
10.
Hydrodynamic equations are derived microscopically for Heisenberg antiferromagnets with inclusion of quasimomentum as an almost conserved quantity. For finite external and anisotropy fields, the hydrodynamic quantities are magnetization, energy and momentum density. At small fields, the propagating mode is essentially an oscillation of the local temperature. For high fields it is a wave in the longitudinal magnetization. In the absence of both fields, the staggered magnetization and not the magnetization itself is coupled to momentum and energy. The propagating mode is mainly an energy wave. The propagating part in the staggered magnetization is inversely proportional to the wavelength. 相似文献
11.
R. Bonin M. d’Aquino G. Bertotti C. Serpico I. D. Mayergoyz 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):47
The stability of large precessional magnetization motions induced by spin-polarized
currents in spin-transfer nano-oscillators is discussed. Quantitative analytical
predictions are obtained for the critical values of spin-polarized injected current and
external magnetic field at which the oscillator magnetization precession becomes unstable.
It is shown that the mechanism leading to instability is parametric resonance of
well-defined pairs of magnetostatically coupled perturbation modes. The amplitude of these
modes grows to large non-thermal values when the oscillator frequency matches the mean of
the natural frequencies of the two coupled modes. Analytical predictions are obtained for
the space-time structure and symmetry of the magnetization patterns that are formed at the
instability. Analytical results are compared with numerical simulations of
spin-transfer-driven magnetization dynamics. 相似文献
12.
Magnetization relaxation processes, which are represented by the Gilbert damping term and the spin torque term in the Landau-Lifshitz-Gilbert (LLG) equation, are described by the radiation-spin interaction (RSI), where the radiation field is produced by magnetization precessional motion itself. It is shown that the LLG equation including the Gilbert damping term and the spin torque term is derived from the spin Hamiltonian containing the RSI. The derivation of the LLG equation is given in a self-consistent method. It is also shown that, according to RSI, the magnitude of the magnetization vector deviates from the magnetization saturation with the order of O(alpha(2)), where alpha is the Gilbert damping parameter. 相似文献
13.
Tomimoto S Matsubara M Ogasawara T Okamoto H Kimura T Tokura Y 《Physical review letters》2007,98(1):017402
Optical manipulation of the magnetic anisotropy is demonstrated for bilayered manganites, La2-2xSr1+2xMn2O7, by means of femtosecond Kerr-rotation measurements. Upon the photoexcitation on the x=0.32 crystal, the magnetization exhibits the precessional motion for about 1 ns, revealing the directional change of the magnetocrystalline anisotropy from the c axis to the ab plane. This change of the anisotropy induces the nonthermal decrease of the c-axis magnetization component for about 1 ns. 相似文献
14.
Within the framework of the Neuringer-Rosenzweig equations, the solutions describing transverse linearly polarized and longitudinal
plane-polarized magnetoacoustic waves are obtained for magnetizable liquids with an arbitrary orientation of the wavevector
and the magnetization vector. In the general case, the group velocity vector of magnetoacoustic waves has a component orthogonal
to the wavevector. For the solutions obtained here, the velocity of sound decreases from the maximal value for a wave propagating
along the magnetization vector to the minimal value corresponding to a wave propagating at right angles to the magnetization
vector. Exact solutions of the equations for magnetizable liquids are obtained in the form of the Riemann waves which are
transformed into the magnetoacoustic waves under investigation for small perturbations of the parameters of the liquid and
magnetic field. 相似文献
15.
J. Goulon A. Rogalev F. Wilhelm N. Jaouen C. Goulon-Ginet Ch. Brouder 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):169-184
We discuss the physical content of X-ray Detected Magnetic Resonance (XDMR), i.e. a novel spectroscopy which uses XMCD to
probe the resonant precession of the local magnetization in a strong microwave pump field. We focus on the simplest case of
a steady-state precession of elemental moments in the non-linear regime of angular foldover. Like XMCD, XDMR is element and
edge selective and could become a unique tool to investigate how precessional dynamics can locally affect the spin and orbital
magnetization of p- or d-projected DOS. This should be possible only in the limit where there is no overdamping due to ultrafast
orbit-lattice relaxation. 相似文献
16.
Weber M. C. Nembach H. Blomeier S. Hillebrands B. Kaltofen R. Schumann J. Carey M. J. Fassbender J. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(2):243-248
All-optical control of the magnetization of polycrystalline exchange bias
bilayer systems is achieved using short picosecond laser pulses. Due to the
photoexcitation, the spin temperature across the interface between the
ferromagnetic and antiferromagnetic layer is elevated, resulting in a
collapse of the interfacial exchange coupling. Thus, within the first 10 ps,
a fast reduction of both the exchange bias field and the coercive field is
observed for three different exchange bias systems comprising both different
ferromagnets and antiferromagnets. The fast thermal unpinning is followed by
a slower heat diffusion dominated relaxation process, which strongly depends
on the thermal conductivity of the used buffer layers and substrates. The
fast optical unpinning can be understood in terms of an internal anisotropy
pulse field capable of triggering ultrafast precessional magnetization
dynamics of the ferromagnetic layer, which makes heat-assisted coherent
magnetization rotation feasible. 相似文献
17.
18.
Stamm C Tudosa I Siegmann HC Stöhr J Dobin AY Woltersdorf G Heinrich B Vaterlaus A 《Physical review letters》2005,94(19):197603
Applying one ultrashort magnetic field pulse, we observe up to 10 precessional switches of the magnetization direction in single crystalline Fe films of 10 and 15 atomic layers. We find that the rate at which angular momentum is dissipated in uniform large angle spin precession increases with time and film thickness, surpassing the intrinsic ferromagnetic resonance spin lattice relaxation of Fe by nearly an order of magnitude. 相似文献
19.
V. M. Korovin 《Technical Physics》2008,53(5):554-561
The subject of consideration is a film of a magnetic fluid applied on the surface of a thin magnetically soft cylinder. Quantities figuring in equations and boundary conditions describing the axisymmetric flow due to capillary and magnetic forces at capillary disintegration of the film are estimated in order of magnitude. The effect of magnetization on the capillary disintegration of the film is studied using simplified equations of ferrohydrodynamics. It is shown that magnetization shifts the range of Rayleigh capillary instability toward longer wave modes. As a result, drops arising at the final stage are larger than in the case of the nonmagnetic liquid. 相似文献
20.
Spin-transfer torque in spin valves usually destabilizes one of the collinear configurations (either parallel or antiparallel) and stabilizes the second one. Apart from this, balance of the spin-transfer and damping torques can lead to steady precessional modes. In this Letter we show that in some asymmetric nanopillars, spin current can destabilize both parallel and antiparallel configurations. As a result, stationary precessional modes can occur at zero magnetic field. The corresponding phase diagram as well as frequencies of the precessional modes have been calculated in the framework of macrospin model. The relevant spin-transfer torque has been calculated in terms of the macroscopic model based on spin diffusion equations. 相似文献