Switching of precession regimes under the conditions of dynamic bistability of magnetization

The dynamics of the magnetization of a single-crystal film under the conditions of dynamic bistability has been investigated using numerical simulation. It has been shown that the use of an additional alternating magnetic field has made it possible to suppress the dynamic bistability of magnetization and to implement one of the two precession regimes depending on the field frequency. Multiple switching between magnetization precessions with different amplitudes can be performed directly from one regime to the other regime due to the corresponding change in the frequency of the additional magnetic field.     

Magnetooptical bistability of a layered semiconductor in the region of exciton absorption

The effect of weak external magnetic fields on the conditions for implementing optical bistability in the region of exciton absorption of layered semiconductors has been theoretically investigated. By the example of the 2H polytype of lead diiodide, it is shown that, changing the strength of an external magnetic field, one can form conditions for implementing bistability and effectively control the position and sizes of the hysteresis loop of exciton absorption.     

Dynamics of a magnetic moment of finite dipolar lattices in the AC field

Dynamic regimes of a magnetic moment of 2 × 2, 3 × 3, and 4 × 4 square dipole lattices in the linearly and circularly polarized ac magnetic field and the perpendicular static field have been investigated. The possibility of regular and chaotic precession dynamics of the magnetic moment of the lattices has been demonstrated. A shift of the main magnetic resonance owing to the dipole–dipole interaction and additional resonances have been revealed. Quasiperiodic regimes and bistability states with a metastable chaotic attractor have been discovered.     

Controlling the optical bistability and transmission coefficient in a four-level atomic medium

A novel four level atomic configuration is proposed for controlling the optical bistability and transmission coefficient with application on all-optical switching. Two circularly polarized components from a weak linearly-polarized probe beam are interacted separately by two transitions of this medium. A coherent coupling field has derived another atomic transition. It is demonstrated that the transmission coefficient of two orthogonally polarized beams at different frequencies can be achieved by adjusting the magnitude of the external magnetic field. It is found that the threshold of the optical bistability can be controlled by magnitude of the external magnetic field. Also, it is shown that optical bistability can be converted to optical multistability by switching the two orthogonally polarized beams.     

THE ION CURRENT BEHAVIOR IN ECR ARGON PLASMA

The ion current density as a function of various system parameters, such as pressure, magnetic field, and microwave power, has been studied by using Faraday cup. The bistability of plasma was observed and discussed.     

Equilibrium configurations and transitions between them in annular magnetic nanodipole systems

The equilibrium states of annular systems of magnetic dipoles have been studied by computer simulation. The bistability conditions under which the total magnetic moment of one of equilibrium configurations is zero, while the magnetic moment of another equilibrium configuration lies in the ring plane and is close to the sum of the magnetic moments of dipoles in the system, have been determined. The realization of other equilibrium configurations has also been demonstrated. We analyze transitions between equilibrium configurations by acting on the system by longitudinal and circular static fields, as well as transitions from the configuration with the maximal magnetic moment of the system to the configuration with zero total magnetic moment after the relaxation of oscillatory regimes excited by a varying field.     

Study of surface magnetic properties in Co-rich amorphous microwires

Magneto-optical investigations carried out on a Co-rich glass-covered amorphous microwire is presented. The appearance of circular magnetic bistability and the influence of tensile stress and high-frequency electric current on the surface magnetization reversal have been studied. The change of the mechanism of the magnetization reversal induced by the high-frequency electric current is also discussed.     

Orientational transitions in ferromagnetic liquid crystals with bistable coupling between colloidal particles and the matrix

We study the orientational response of a ferromagnetic liquid crystal that is induced by magnetic and electric fields. A modified form of the energy of the orientational interaction between magnetic impurity particles and the liquid crystal matrix that leads to bistable coupling is considered. It is shown that apart from magnetic impurity segregation, first-order orientational transitions can be due to the bistability of the potential of the orientational coupling between the director and the magnetization. The ranges of material parameters that lead to optical bistability are determined. The possibility of first-order orientational transitions is analyzed for the optical phase difference between the ordinary and extraordinary light rays transmitted through a ferronematic cell. It is shown that an electric field applied in the given geometry considerably enhances the magneto-orientational response of the ferronematic.     

Equilibrium orientation states in a system of two magnetic layers with antiferromagnetic coupling

The equilibrium orientations of magnetic moments are found for a system of two antiferromagnetically coupled magnetic films in an external magnetic field. Field intervals are found where the noncollinear and orientational bistability states occur, resulting in the orientation hysteresis and phase transition.     

Tunable optical bistability at microwave frequency based on 1D sandwich photonic structure consisting of a nonlinear dielectric slab and two magnetized cold plasma layers

In this paper, tunable optical bistability that denotes the relationship between input intensity and output intensity is numerically investigated in the microwave frequency region based on the one-dimensional (1D) sandwich photonic structure consisting of a Kerr-type nonlinear material slab and two magnetized cold plasma layers. Results show that, in the case of TM-polarized electromagnetic wave, width and switching thresholds of the bistability loops are dependent on the working frequency, initial incidence angle, layer thickness, plasma density, and external magnetic field, which should be judiciously selected to obtain a required bistability behavior. Compared to the case of switch-down threshold, the switch-up threshold in the bistability loop is more sensitive to the changes of parameters. Through this study, the suggested 1D sandwich photonic structure is beneficial to the all-optical signal processing.     

Stochastic resonance between the limiting cycles of precession dynamics

A new type of stochastic resonance that arises between two precession modes under dynamic bistability conditions and is excited by an alternating magnetic field, including a harmonic signal and a white noise, has been studied using a numerical analysis of the uniform magnetization precession in a thin film. The spectrum of the steady-state dynamics of the system at stochastic resonance has been investigated, and its distinctive features have been revealed for the longitudinal and transverse orientations of the additional alternating field.     

Equilibrium values and dynamics of the net magnetic moment of a system of magnetic dipoles

Equilibrium states of different systems formed by coupled spherical bodies with dipole magnetic moments have been investigated using a numerical analysis. The bistable states and the corresponding values of the net magnetic moment are determined for a number of planar and three-dimensional systems of dipoles, and the conditions providing the existence of orientational configurations of coupled dipoles involved in the bistability are analyzed. The disturbances of the magnetic moment due to the quasi-static passage of an additional dipole and the dynamic modes excited by a homogeneous alternating magnetic field and represented by periodic, quasi-periodic, and chaotic oscillations of the magnetic moment of the system are considered for several types of systems. The bifurcation diagrams of the dynamic modes are constructed, and the specific features typical of the systems under consideration are revealed.     

Optical bistability in a defect slab with a negative refractive quantum dot nanostructure

We demonstrate optical bistability (OB) in a defect slab doped V-type four-level InGaN/GaN quantum dot nanostructure in the negative refraction frequency band. It has been shown that the OB behavior of such a quantum dot nanostructure system can be controlled by the amplitude of the driving fields and a new parameter for controlling the OB behavior as thickness of the slab medium in the negative refraction band. Meanwhile, we show that the negative refraction frequency band can be controlled by tuning electric permittivity and magnetic permeability by the amplitude of the driving fields and electron concentration in the defect slab doped. Under the numerical simulations, due to the effect of quantum coherence and interference, it is possible to switch bistability by adjusting the optimal conditions in the negative refraction frequency band, which is more practical in all-optical switching or coding elements, and technology based nanoscale devices.     

Hysteresis and memory of the magnetic resonance of conduction electrons in solids. From bistability to stochastic resonance

The magnetic resonance line of conduction electrons in solids may exhibit bistable hysteresis if several conditions are fulfilled. Its mechanism is presented and the manifestation of bistability in the ESR of conduction electrons in single crystal and polycrystalline samples is discussed. The characteristics of the dynamics of the bistability show that bistable resonance can be assimilated to one-dimensional overdamped motion of the spin system in the nuclear field space, driven by a bistable potential. It is shown for the first time that noise acting on this bistable resonance can create order, by the phenomenon of stochastic resonance.     

Nonlinear dynamic magnetization regimes in (100) ferrite-garnet films

To study the nonlinear dynamics of a uniformly precessing magnetization in perpendicularly magnetized (100) ferrite-garnet films, equations of motion are numerically solved over a wide ac field frequency range. Bifurcation changes in the magnetization precession and the states of dynamic bistability have been detected. The conditions of high-amplitude regular and stochastic dynamic regimes are revealed, and the possibilities of controlling these precession regimes by applied magnetic fields are shown.     

Specific features in precession dynamics of magnetization of a uniaxial magnetic film

The precession dynamics of the magnetization of a film with in-plane uniaxial anisotropy in the case of its biasing along the hard magnetization axis has been analyzed by numerically solving the Landau-Lifshitz equations. It has been revealed that the ferromagnetic resonance spectrum near the magnetic anisotropy field exhibits an additional peak, which is associated with the angular bistability due to the presence of two symmetric angular equilibrium positions. The trajectories of precession motion during biasing along the hard magnetization axis differ substantially from the trajectories corresponding to the biasing along the easy axis.     

Optical bistability with surface polaritons in layered structures containing left-handed metallic magnetic composites

We present the exact results on optical bistability (including angular and frequency bistabilities) with surface polaritons in layered structures containing left-handed metallic magnetic composite (MMC). The bistable behaviors of the reflected field are revealed for the Kretschmann and Sarid geometries, respectively. The results show that the properties of the angular and frequency bistabilities are quite similar, namely, the optical bistability with the surface polaritons can occur only when the angle or frequency detunings and the substrate’s nonlinear coefficient have the same sign. For the Kretschmann geometry, the surface polaritons can exist in the pass band due to the negative refraction effect. In the Sarid geometry, the excitation of the long-range surface polaritons in the stop band results in a lower optical bistability threshold compared with the Kretschmann geometry. The above conclusions are valid only for the frequency range where the MMC is left-handed.     

Optical bistability at angular incidence in a one-dimensional photonic crystal containing single negative materials

Nonlinear wave propagation is studied theoretically in a one-dimensional photonic band gap structure containing single negative materials. It is found that Kerr nonlinearity is greatly enhanced near the lower edge of a recently explored angular gap for transverse magnetic polarized light. Consequently, optical bistability is achieved at very low values of input intensity in a periodic structure composed of only a few repeating units. The characteristics of optical bistability are affected only slightly with the variation of the incident angle and thickness ratio of the layers. The effect of losses is also found to be relatively insignificant in such a small structure.     

Magnetic bistability and controllable reversal of asymmetric ferromagnetic nanorings

Magnetization reversals through the formation of a vortex state and the rotation of an onion state are two processes with comparable probabilities for symmetric magnetic nanorings with a radius of about 50 nanometers. This magnetic bistability is the manifestation of the competition between the exchange energy and the magnetostatic energy in nanomagnets. The relative probability of the two processes in symmetric nanorings is dictated by the ring geometry and cannot be altered after fabrication. In this work, we report a novel type of nanorings--asymmetric nanorings. By tuning the asymmetry, we can control the fraction of the vortex formation process from about 40% to nearly 100% by utilizing the direction of the external magnetic field. The observed results have been accounted for by the dependence of the domain-wall energy on the local cross-section area for which we have provided theoretical calculations.     

Two optical bistability domains in composites of metal nanoparticles with nonlinear dielectric core

It is shown that the local field in metal spherical particles with a dielectric core in an external varying electric field has two maxima at two different frequencies. The second maximum becomes more important with an increment in the metal fraction. Due to the nonlinear dielectric function of the core, the composite of these inclusions may have two optically induced bistability domains at different frequencies. At rather high metal fraction, two bistability domains merge and form one entire bistability domain. The parameters of these domains are studied numerically. The paper focuses on the second bistability domain, which has not been discussed in the literature so far. This domain exists in a comparatively narrow frequency range and its onset fields are lower than those of the first bistability domain. The lowest bistability onset fields are obtained in the entire domain. This peculiarity of the optical induced bistability in the metal composite with small dielectric cores can be attractive for possible applications.