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Magnetization dynamics in uniformly magnetized nanomagnets excited by time-harmonic (AC) external fields or spin-polarized injected currents is considered. The analysis is focused on the behaviour of the AC-excited dynamics near saddle equilibria. It turns out that this dynamics has a chaotic character at moderately low power level. This chaotic and fractal nature is due to the phenomenon of heteroclinic tangle which is produced by the combined effect of AC-excitations and saddle type dynamics. By using the perturbation technique based on Melnikov function, analytical formulas for the threshold AC excitation amplitudes necessary to create the heteroclinic tangle are derived. Both the cases of AC applied fields and AC spin-polarized injected currents are treated. Then, by means of numerical simulations, we show how heteroclinic tangle is accompanied by the erosion of the safe basin around the stable regimes. [ABSTRACT FROM AUTHOR]

The switching process of a magnetic spin-valve nanosystem subject to spin-polarized current pulses is considered. The dependence of the switching probability on the current pulse duration is investigated. The further application of a transverse field along the intermediate anisotropy axis of the particle is used to control the quasi-random relaxation of magnetization to the reversed magnetization state. The critical current amplitudes to realize the switching are determined by studying the phase portrait of the Landau-Lifshtz-Slonczewski dynamics. Macrospin numerical simulations are in good agreement with the theoretical prediction and demonstrate reliable switching even for very short (below 100 ps) current pulses. [ABSTRACT FROM AUTHOR]

Stochastic magnetization dynamics in uniformly magnetized nanomagnets is considered. The system is assumed to have rotational symmetry as the anisotropy axis, the applied field, and the spin polarization are all aligned along an axis of symmetry. By appropriate integration of the Fokker-Planck equation associated to the problem, the stochastic differential equation governing the evolution of the angle between the magnetization orientation and the symmetry axis is derived. The drift terms present in this equation contain a noise-induced drift term, which, in combination with drift terms of deterministic origin, can be written as the derivative of an effective potential. Superparamagnetic-like transitions are studied in connections with the bifurcations of the effective potential as temperature and excitation conditions are varied. [ABSTRACT FROM AUTHOR]

A study was conducted to show that excess eddy current losses can be explained by the unusual nature of nonlinear diffusion of electromagnetic fields in magnetically nonlinear conducting laminations. The nature of the nonlinear diffusion promotes the breakdown of the classical uniformity assumption. The assumption is associated with the distribution of magnetic flux density even at low frequencies.

Methods of nonlinear-dynamical-system theory are applied to the study of magnetization dynamics under the action of microwave magnetic fields. In the case of a system with uniaxial anisotropy subject to a circularly-polarized microwave field, the conditions are derived under which the magnetization reversal field is substantially reduced by the application of the microwave field. The dependence of magnetization switching on microwave-field-pulse duration is discussed and analytical expressions are derived for the minimum pulse duration leading to switching. [ABSTRACT FROM AUTHOR]

The magnetostriction of magnetically diluted (Lu3-xBixFe5-yGayO12) (BiLuIG) thin films grown by epitaxial deposition on (111)-oriented gallium gadolinium garnet substrates was optically studied using the technique based on the bending of samples by an external applied pressure. The real-time optical observations of stripe magnetic domains and their evolution under external applied magnetic fields and applied stresses are reported. The observed changes in the magnetic domain structure are used to infer the magnetostriction coefficient λ111 of garnet films. [ABSTRACT FROM AUTHOR]

Analysis of the penetration of electromagnetic fields into hard superconductors reveals that the superconductors exhibit superconducting hysteresis. The analysis is performed with the assumption that ideal resistive transitions occur in these superconductors. The 'power law' provides a description of the superconducting hysteresis.

The air-core designs of Ethernet transformers in which the reduction of winding magnetic coupling is compensated by increasing the cross-winding capacitance coupling are described. The studies have shown that the capacitive cross-winding coupling has resulted in desirable characteristics of air-core transformers that are similar to those of ferrite core Ethernet transformers.

BiPrGdLu garnet films epitaxially grown on (210)-oriented substrates, which can be used as magneto-optical imagers, are studied. The garnet films have shown the phenomena of easy magnetization plane and the reduction of thickness of the garnet films through chemical etching has increased the clarity and spatial resolution of magneto-optical imaging.

An iterative algorithm for hysteresis compensation in micropositioning applications is described. The results of the testing of this iterative algorithm in tracking problems related to magnetic recording are presented.

The implicit midpoint time-integration technique is applied to the stochastic Landdau-Lifshitz-Gilbert (LLG) equation. The numerical scheme converges to the Stratonovich solution in the limit of vanishing time step and it preserves the magnetization magnitude and the main energy balance properties of the LLG equation independently of the time step.

Precessional switching of magnetization in perpendicular media induced by short rectangular pulses applied at arbitrary angles with respect to anisotropy axis are studied. The expressions for critical magnetic fields and pulse durations that guarantee precessional magnetization reversals are derived.

A dynamic track-following technique is developed that enables real-time reading of on-track data from off-centered hard disks on a spin stand. This technique makes use of piezoelectric transducers to dynamically control the radial displacement of the read head to follow off-centered tracks.

The 'inverse problem' approach to the analysis of precessional switching of magnetization in perpendicular media is presented. This approach is purely algebraic in nature and it leads to the direct calculations of expressions for magnetic-field pulses that guarantee the precessional switching.

The spin-stand imaging technique is developed for the imaging and diagnostics of whole-track hard disk data from off-centered disks. It is shown that the hard disk tracks are nearly sinusoidally modulated in he radical direction due to eccentricity.

The average technique is used for the analysis of magnetization relaxations to equilibrium. The averaging technique is compared with the numerical solutions of the Landau-Lifshitz equation and found to be leading to the first order separable differential equation for the free energy that can be used instead of the Landau-Lifshitz equation to study magnetization relaxations.

The inverse problem approach for analysis of precessional switching of magnetization in thin films is discussed. Explicit expressions for magnetic field pulses guarantee precessional switching for this approachds

A method for the calculation of spectral density of hysteretic system driven by stochastic inputs is discussed. This technique is based on the mathematical machinery of stochastic processes on graphs.

Analytical solutions to the Landau-Lifshitz equation for 'damping' and 'precessional'magnetization switchings in ferromagnetic objects with uniaxial anisotropy are discussed. These solutions lead to the expressions for switching times and critical fields.