Magnetostatic Excitation Research Articles

Approximate periodic solutions to microelectromechanical system oscillator subject to magnetostatic excitation

A way to obtain approximate periodic solutions to nonlinear oscillators arising in a microelectromechanical system (MEMS) is presented for the case of zero initial conditions and magnetostatic excitation. The frequency–amplitude relationship is derived by adopting He′s frequency formulation. The obtained analytical results are illustrated graphically. The proposed simple approach gives the fast insight into the dynamics of the singular oscillator and can be useful for design of MEMS devices.

FEA Aided Design of Power Shunt-Reactors with Discretely-Distributed Air-Gaps

In this paper, a Finite Element Analysis (FEA) aided design methodology for power shunt-reactors is proposed. The lack of simple and straightforward expressions for the calculation of gap-loss component and leakage inductance is the bottleneck of a fully analytical design procedure. To tackle with the difficulty arising from the calculation of gap-loss, the total air-gap is subdivided into several discretely-distributed air-gaps. This makes the gap-loss component negligibly small in comparison with the core loss. The preliminary design of the target reactor can therefore be achieved analytically by using an initial estimate of percentage leakage inductance. The preliminary design can then be tested and fine-tuned by using Maxwell 3D Magnetostatic Excitation and 2D Transient Sinusoidal Current Excitation tools,in the second phase of the recommended design procedure. The reactor under design can be optimized according to one of minimum Initial Cost, minimum Total Loss or minimum Present Value Cost design objectives, upon the request of the customer or the designer. Advantages and disadvantages of Maxwell 3D and 2D Transient Sinusoidal Current Excitation and Transient Sinusoidal Voltage Excitation analyses facilities are also discussed in the paper

An active resonator based on magnetic films for near field microwave microscopy

An active resonator perturbation method is introduced as a sensitive and versatile way to probe material properties in near field microwave microscopy. An active ring microwave oscillator based on magnetostatic excitations in a yittrium iron garnet thin film has been developed with a coaxial near field probe connected directly to the resonator ring. The probe tunes the resonator’s emission frequency, and the high Q-factor of the magnetostatic oscillations allows for a very sensitive spatially resolved probe of surface impedance and material properties with a much larger dynamic range than conventional resonant probes for microwave microscopy.

Calculation of spin wave spectra in magnetic nanograins and patterned multilayers with perpendicular anisotropy

We study spin-wave excitations in multilayered magnetic nanograins composed of a stack of planes with perpendicular magnetic anisotropy. The inhomogeneity is modeled through the multiple repetition of a unit cell composed of layers of two different magnetic materials. The magnetic inhomogeneity along the central axis is found to split the frequency spectrum of magnetostatic excitations into two bands, while into the number of bands in the spectrum of exchange spin waves. We show that this difference in behavior is a result of the underlying long- and short-range interactions, respectively. We describe a way of increasing the role of the dipolar interactions in the formation of magnonic bands in patterned magnetic multilayers with perpendicular anisotropy, which can allow one to obtain ferromagnetic resonance spectra with two strong absorption peaks in low and high frequencies up to the sub-THz range. Our findings open a new area for modeling the spin-wave spectra of patterned magnetic multilayers with potential applications, and for studying the role of the microscopic magnetic structure in forming spin-wave spectra.

Impedance of a planar solenoid with a thin magnetic core

The high-frequency impedance of a planar solenoid with a thin magnetic core is theoretically investigated using the magnetostatic Green’s function formalism. It is shown that the electrical behavior of the solenoid depends on how the magnetic field induced by the current-carrying coil is coupled to the different magnetostatic modes of the core. The magnetic response of the core in each mode is determined by an effective susceptibility matrix which depends on exact, but mode-dependent demagnetization factors. Those factors determine the frequency of the magnetostatic excitations of the core, manifested as resonances in the impedance of the solenoid. Using the formalism developed, the effect of the core width and magnetic loss on the impedance of the device is studied.

Interaction of magnetostatic excitations with 90° domain walls in micrometer-sized permalloy squares

We investigate the magnetic excitations in soft magnetic squares and in particular the role of domain walls in such Landau flux-closure structures. For this we combine synchrotron-based photoemission electron microscopy and simulations using the Landau-Lifshitz-Gilbert equation. We show that the 90\ifmmode^\circ\else\textdegree\fi{} N\'eel walls in such squares act as efficient barriers for magnetic excitations that absorb the incoming energy. Because of the finite elasticity, the absorbed energy leads to oscillations of the domain walls, which subsequently cause emission of sharp wave fronts.

Tunable high-frequency magnetostatic waves in Thue-Morse antiferromagnetic multilayers

We theoretically studied the magnetostatic excitation in self-similar antiferromagnetic(AF)/nonmagnetic(NM) multilayers, where the AF and NM layers were arranged in a Thue-Morse sequence. The dispersion relation of magnetostatic spin waves and the precession amplitude of the total magnetization were achieved. It is shown that the distribution of eigenfrequencies possesses two bands of dual structures and each subband presents a hierarchical feature. The states in the finite system can be categorized to three types: critical states in the subband, extended states in the band, and localized surface states in the gaps. The multiformity in frequency spectra leads to the tunable magnetostatic wave, which may have potential applications in designing devices of magnetostatic waves for microwave communications.

Magnetostatic excitations in quasiperiodic antiferromagnetic superlattices

The magnetostatic excitation in antiferromagnetic superlattices (antiferromagnetic/nonmagnetic layered structure) grown following the Fibonacci sequence has been studied. The dispersion relations of the magnetostatic spin wave spectra and the precession amplitudes of the total magnetization in each layer are numerically obtained. The eigenfrequency spectra are divided into two branches, ${\ensuremath{\omega}}^{\ensuremath{-}}$ and ${\ensuremath{\omega}}^{+}.$ For each branch, the distribution of eigenfrequency spectra exhibits triadic Cantor-set subband structures with self-similar features. The eigenfrequency spectra distribution strongly depends on the in-plane wave vector and the thickness of antiferromagnetic and nonmagnetic layers. For most of the eigenfrequencies, especially in the triadic regions, the profiles of precession amplitudes of total magnetization in the quasiperiodic system are critical and self-similar. For the eigenfrequencies near the edges of bands, the profiles of precession amplitudes of total magnetization are extended with a sine modulation. Besides the critical and extended states, a few states at the edges of the subbands are still quasilocalized. The corresponding profiles of precession amplitudes of total magnetization either decay or oscillate with exponential attenuation from the surface into the film.

Magnetic excitations in semiconductor superlattices.

We present a theoretical study of magnetostatic excitations in ferromagnetic and antiferromagnetic films and in superlattices composed of alternating layers of such materials with paramagnetic and nonmagnetic substances. The motivation for this study is the possibility of observation of these modes of motion in slabs and superlattices of diluted magnetic semiconductors by inelastic light scattering. We classify the excitations in films as ``bulklike'' and ``surfacelike.'' Periodic excitations propagating along the growth axis of a superlattice occur which can be classified as ``pure bulk'' modes if the magnetization of the media behaves sinusoidally in each layer; as ``pure interface'' modes if they propagate along the boundary separating adjacent layers while their amplitudes decay exponentially within each medium and as ``bulk-interface'' modes when a behavior occurs having ``bulk'' character in one medium and ``surface'' character in the other. We give an analysis of the dispersion relations of these modes and the ranges within which their frequencies lie.