共查询到20条相似文献,搜索用时 0 毫秒
1.
The possibility to excite ferromagnetic magnons with very large k is analyzed theoretically. The proposed excitation mechanism is analogous to the first-order Suhl instability and takes place via non-linear processes involving localized modes associated with imputities in ferromagnetic insulators. A rough estimate of the critical power of a far-infrared laser source necessary to attain the instability threshold shows that the processes are experimentally feasible. 相似文献
2.
S. Krompiewski 《Physics letters. A》1979,71(1):133-136
The Wolff-Clogston model for a dilute alloy with interactions between electrons in the host metal is considered. A localized magnon mode is suggested to appear above the magnon band for a fcc structure, provided the impurity is “less magnetic” (δU<0) than a strongly ferromagnetic host. 相似文献
3.
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
4.
M. Tsoi 《Journal of magnetism and magnetic materials》2002,240(1-3):103-107
We report the detection of electromagnetic waves radiated by current-driven magnons in a Co/Cu magnetic multilayer. The magnons were excited by means of a high current density ≈108 A/cm2 injected into the multilayer through a point contact. The point contact itself was used as a high frequency mixer to mix electromagnetic waves radiated by the current-driven magnons with externally generated microwave radiation. Here the external microwaves are used as a direct probe of the high-frequency behavior and partial phase coherence of the current-induced excitations. When the external frequency equaled the frequency of the magnons generated in the multilayer a DC voltage was found to develop across the contact. Investigation of how this voltage varies with exciting current, magnetic field, and microwave frequency provides detailed information on the spectrum of the current-driven magnons. Our observations support the feasibility of a spin-wave maser, or spin-wave amplification by stimulated emission of radiation. 相似文献
5.
H. Al-Wahsh 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):445-451
We study, in the frame of the discrete dipole approximation, the
magnons propagation through a simple multiplexing device made of
chains of magnetic nanoparticles along which a small chains (called
a resonators) is attached. We show that this simple structure can
transfer with selectivity one magnon frequency from one chain to the
other, leaving neighbour magnonic frequencies unaffected. With an
appropriate choice of the geometrical (or magnetic) parameters of
the structure, it is possible to control the desired magnon
ejection. A general analytical expression for the transmission
coefficient is given for various structures of this kind within
the framework of the Green’s function method. The amplitude, the
phase, and the phase time of the transmission are discussed as a
function of frequency. These results may opens new perspectives for
constructing, more efficient and more compact, magnonic devices such
as narrow-frequency microwave multiplexers. 相似文献
6.
The high frequency magnon generation by nonequilibrium electrons polarized opposite the magnetization vector is investigated. At some conditions the avalanche-type generation of magnons with wavevectors along the magnetization takes place and the magnon system becomes unstable. 相似文献
7.
A magnon‐phonon interaction model is set up in a two‐dimensional ferromagnetic compound square‐lattice system. Using the Matsubara Green function theory we calculated the magnon dispersion curves on the main symmetric line in Brillouin zone, compared the influences of the magnetic ion optical phonon with non‐magnetic ion optical phonon on the magnetic excitation of the system and discussed the influences of various parameters on the magnon softening. The lower Debye temperature of ferromagnetic materials is, the more likely the magnon softening occurs. It turned out that the optical phonon‐magnon coupling plays an important role on the magnon softening, the longitudinal optical phonon contributes the most to the magnon softening and magnon damping. It is also found that the contribution of the non‐magnetic ion to the magnon softening and magnon damping is more significant than that of magnetic ion when the mass of the magnetic ion is less than that of the non‐magnetic ion, or the mass of magnetic ion and the non‐magnetic ion are equal. 相似文献
8.
Thomas Unnerstall 《Journal of statistical physics》1989,54(1-2):379-403
The irreversible macroscopic dynamics of the Josephson junction coupled to external wires acting as a current source is derived rigorously from the underlying microscopic Hamiltonian quantum mechanics. The external systems are treated in the singular coupling limit. The use of this limit is explicitly justified via an interpretation of the singular coupling limit in terms of the relative magnitudes of system, reservoir, and coupling energies. The qualitative behavior of the macroscopic dynamical equations is shown to depend sensitively and crucially on the interaction between the wires and the superconductors and on the size of the wires: the dc Josephson effect only happens when one lets Cooper pairs be driven into the junction by collective (i.e., small) reservoirs. 相似文献
9.
B. K. Shivamoggi 《Czechoslovak Journal of Physics》1988,38(6):638-642
Nonlinear stabilization of ion-acoustic current-driven instability brought about by the electron resonance broadening is studied The electric field spectrum in the saturated state is shown to agree with the known stationary ion-acoustic turbulence spectrum. 相似文献
10.
Edge-localized modes (ELMs) are cyclic disturbances in the outer region of tokamak plasmas that are influential in determining present and future tokamak performance. In this Letter, we outline an approach to modeling ELMs in which we envisage toroidal peeling modes initiating a Taylor relaxation [Phys. Rev. Lett. 33, 1139 (1974)10.1103/PhysRevLett.33.1139] of a tokamak outer region plasma. Relaxation produces a peeling destabilizing flattened edge current profile and a stabilizing plasma-vacuum current sheet; the balance between the two determines the radial extent of the relaxed region. The model can be used to predict the energy losses due to an ELM and reproduces experimentally observed variations with edge safety factor and plasma collisionality. There is an intrinsic "deterministic scatter" in the model that also accords with observation. 相似文献
11.
Starting from the stochastic Landau-Lifschitz-Gilbert equation, we derive Langevin equations that describe the nonzero-temperature dynamics of a rigid domain wall. We derive an expression for the average drift velocity of the domain wall r(dw) as a function of the applied current, and find qualitative agreement with recent magnetic semiconductor experiments. Our model implies that at any nonzero-temperature r(dw) initially varies linearly with current, even in the absence of nonadiabatic spin torques. 相似文献
12.
磁子是自旋波量子化的准粒子。磁子具有在绝缘磁性材料中无热耗散、低阻尼、长距离传输自旋的优势,避免了因电荷流动而产生焦耳热,可以克服日益显著的器件发热问题,因此磁子器件在低功耗信息存储与计算领域具有潜在应用前景。文章首先介绍了自旋波和磁子的概念,磁子具有的优势和研究价值;然后总结了磁子在铁磁和反铁磁绝缘体中输运以及新型磁子器件方面的最新研究结果;最后详细介绍了室温下实现磁子转矩驱动磁矩翻转的最新研究工作。这些工作对发展磁子学,实现低功耗、高速磁子型器件及应用具有较为重要的现实意义。 相似文献
13.
The mechanisms of the magnetization switching of magnetic multilayers driven by a current are studied by including exchange interaction between local moments and spin accumulation of conduction electrons. It is found that this exchange interaction leads to two additional terms in the Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both terms are proportional to the transverse spin accumulation and have comparable magnitudes. 相似文献
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15.
V. Čápek 《Zeitschrift für Physik B Condensed Matter》1985,60(1):101-105
The Haken-Strobl-Reineker model of the excitation transfer is generalized to finite temperatures and non-periodic systems taking into account a quantum character of the stochastic field acting on excitons. Possibly asymmetric hopping rates yielding contingently different asymptotic site-occupation probabilities for different sites in non-periodic systems appear. A simple example is discussed corresponding to exciton tapping and radiative decay at the trap. 相似文献
16.
Tim Willaert Bart Cleuren Christian Van den Broeck 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(6):1-4
We show that the scaled cumulant generating and large deviation function, associated to a two-state Markov process involving two processes, obey a symmetry relation reminiscent of the fluctuation theorem, independent from any conditions on the transition rates. The Legendre transform leading from the scaled cumulant generating function to the large deviation function is performed in an ingenious way, avoiding the sign problem associated to taking a square root. Applications to the theory of random walks and to the stochastic thermodynamics for a quantum dot are presented. 相似文献
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In the TCV tokamak, the m/n = 2/1 island is observed in low-density discharges with central electron-cyclotron current drive. The evolution of its width has two distinct growth phases, one of which can be linked to a "conventional" tearing mode driven unstable by the current profile and the other to a neoclassical tearing mode driven by a perturbation of the bootstrap current. The TCV results provide the first clear observation of such a destabilization mechanism and reconcile the theory of conventional and neoclassical tearing modes, which differ only in the dominant driving term. 相似文献