Spin Waves In Magnetic Films Research Articles

Bias-free spin-wave propagation in a micrometer-thick ferrimagnetic film with perpendicular magnetic anisotropy

The isotropic transmission of magnetostatic forward volume spin waves in magnetic films with perpendicular magnetic anisotropy (PMA) is shown to be useful in the implementation of magnon-based micro-conduits. However, to our knowledge, non-magnetic-bias-field spin-wave propagation in a PMA magnetic insulator has not been achieved yet, which constrains the development of magnonic information devices and systems. Herein, we demonstrate a robust, bias-free spin-wave transmission in an 18.5-μm-thick bismuth-doped thulium iron garnet film with PMA. This ferrimagnetic film grown by liquid phase epitaxy exhibits high quality in both its crystal structure and its chemical composition and displays a large PMA field of ∼173 mT. The bias-free and reciprocal propagation of spin waves is demonstrated by all-electrical spectroscopy and provides a group velocity of 4.90 km s−1 and a decay length of 20.5 µm at zero magnetic field. Direct imaging of the remnant state indicates that the bias-free spin waves propagate along the oppositely oriented stripe domains with Bloch-type walls, which are formed by in-plane pre-magnetization. Our work contributes to the construction of isotropic charge-free micro-circuits with high levels of integration and nonvolatility.

Local non-linear excitation of sub-100 nm bulk-type spin waves by edge-localized spin waves in magnetic films

The excitation of high-frequency short-wavelength spin waves is a challenge limiting the application of these propagating magnetization disturbances in information processing systems. We propose a method of local excitation of the high-frequency spin waves using the non-linear nature of magnetization dynamics. We demonstrate with numeric simulations that an edge-localized spin wave can be used to excite plane waves propagating obliquely from the film's edge at a doubled frequency and over twice shorter in wavelength. The excitation mechanism is a direct result of the ellipticity of the magnetic moment precession that is related to the edge-mode propagation. As a consequence, the magnetization component tangential to the equilibrium orientation oscillates with doubled temporal and spatial frequencies, which leads to efficient excitation of the plane spin waves. The threshold-less non-linear process of short-wavelength spin-wave excitation proposed in our study is promising for integration with an inductive or point-like spin-torque source of edge spin waves.

Spin Waves in Magnetic Films with Antidots

This review presents the data of the experimental investigation of the propagation and decay of magnetostatic spin waves (MSWs) obtained when analyzing the Brillouin light scattering data in yttrium iron garnet films. It is shown that the effect of nonreflected wave connected with artificial antidots in films leads to a significant increase in the intensity and propagation length of the magnetostatic spin waves in yttrium iron garnet.

Correlation receiver of below-noise pulsed signals based on parametric interactions of spin waves in magnetic films

A correlation receiver capable of receiving pulsed microwave signals having amplitudes substantially below the noise level is proposed and experimentally realized. The device is based on the parametric interaction of two contra-propagating spin waves excited by the received microwave signal and the reference pulsed signal, containing information about the received signal shape, in a ferrite film waveguide. The output nonlinear correlation signal having the doubled carrier frequency and the signal-to-noise ratio enhanced by several orders of magnitude is received by a dielectric resonator coupled to an output microwave transmission line.

Field-induced transition from parallel to perpendicular parametric pumping for a microstrip transducer

Microstrip transducers used for the excitation of spin waves in magnetic films possess two characteristic properties: high spatial localization of the microwave magnetic field and the presence of field components parallel and perpendicular to the bias field. Here, the effects of these features on the process of parametric pumping are presented. By microwave measurements of the spin-wave instability threshold a transition from parallel pumping to perpendicular pumping at the critical field with the minimal threshold is observed. This transition is accompanied by a sharp threshold increase above the critical field due to the spatial confinement of the pump region.

Coupled Modulational Instability of Copropagating Spin Waves in Magnetic Thin Films

This letter reports the first results on the coupled modulational instability of copropagating spin waves in a magnetic film. Strong instability was observed for the two waves with either attractive or repulsive nonlinearity. If the two waves have attractive nonlinearity, the instability leads to the formation of bright solitons. If the two waves have repulsive nonlinearity, the process results in the formation of black solitons. The instability was also observed for the two waves in separated attractive-repulsive nonlinearity regimes.

Excitation of Spin Waves by Spin-Polarized Current in Magnetic Nano-Structures

An approximate analytic theory describing excitation of microwave spin waves by spin-polarized direct current in magnetic nano-structures is presented. The theory is based on the classical Hamiltonian formalism for spin waves in magnetic films, and uses the idea that spin-polarized current passing through the ldquofreerdquo layer of a magnetic nano-structure creates in this layer an effective negative damping for spin wave modes. The developed theory in the macrospin approximation describes current-induced uniform magnetization precession both near the minimum and maximum of magnetic energy of the ldquofreerdquo layer. The same theory, also, provides a framework for the description of excitation of supercritically unstable spatially nonuniform and propagating spin wave modes.

The Role of Next-Nearest Neighbours for the Existence Conditions of Subsurface Spin Waves in Magnetic Films

Spin-wave energies and respective band structures throughout the two-dimensional Brillouin zone are investigated in magnetic (cubic) thin films for the surface orientations sc(110), bcc(110) and fcc(110). We apply the Heisenberg localized spin model assuming exchange nearest (NN) and next-nearest (NNN) neighbour interactions and elucidate the role of the geometrical disposition of the NN and NNN neighbourhoods for the emergence of surface (SSW) and subsurface spin waves (SSSW). The necessary condition for the emergence of SSSW is found to require the NNN bonds to be cut at the surface obliquely thereto.

The Role of Next-Nearest Neighbours for the Existence Conditions of Subsurface Spin Waves in Magnetic Films

Spin-wave energies and respective band structures throughout the two-dimensional Brillouin zone are investigated in magnetic (cubic) thin films for the surface orientations sc(110), bcc(110) and fcc(110). We apply the Heisenberg localized spin model assuming exchange nearest (NN) and next-nearest (NNN) neighbour interactions and elucidate the role of the geometrical disposition of the NN and NNN neighbourhoods for the emergence of surface (SSW) and subsurface spin waves (SSSW). The necessary condition for the emergence of SSSW is found to require the NNN bonds to be cut at the surface obliquely thereto.

Mappings leading to randomization of an envelope of high-intensity spin waves

An experimental investigation was made of the transition to chaos in the self-modulation of high-intensity surface spin waves in magnetic films with nonlinearity caused by a three-magnon interaction. One-dimensional mappings leading to randomization of the envelope are constructed. It is shown that these mappings are universal and do not depend on the scenario for the transition to chaos.

The Role of Oblique-to-Surface Disposition of Neighbours in the Emergence of Surface Spin Waves in Magnetic Films

This work is aimed at a numerical investigation of the spin-wave energies and respective band structures throughout the two-dimensional Brillouin zone in 'magnetic (cubic) thin films for the surface orientations sc(001), bcc(001) and fcc(001). We apply the Heisenberg localized spin model assuming exchange nearest (NN) and next-nearest (ΝΝΝ) neighbour interactions and elucidate the role of the geometrical disposition of the NN and ΝΝΝ neighbourhoods for the emergence of the surface spin-waves. The necessary condition for the emergence of the surface spin-waves is turned out to require the bonds to be cut at the surface obliquely thereto irrespective of whether these oblique 'interactions are of the NN or ΝΝΝ type. PACS numbers: 75.70.—i, 75.40.Gb, 75.30.Ds

Antiresonant behavior of light cross section in mode crossing of spin waves in magnetic films

We calculate the Brillouin cross section of the surface spin wave in a thin magnetic film in the frequency--wave-vector range where a mode crossing with a spin bulk wave occurs. A macroscopic partial waves approach that takes into account dipole and exchange interactions is used. It is found that the cross section shows a Fano-type antiresonant behavior.

Direct observation of two-dimensional self-focusing of spin waves in magnetic films

An observation of self-focusing of dipolar spin waves in garnet film media is reported. In particular, we show that the quasistationary diffraction of a finite-aperture spin-wave beam in a focusing medium leads to the concentration of the wave power in one focal point rather than along a certain line (channel). The obtained results demonstrate the wide applicability of nonlinear spin-wave media to study nonlinear wave phenomena using an advanced combined microwave--Brillouin-light-scattering technique for a two-dimensional mapping of the spin-wave amplitudes.

Envelope solitons of highly dispersive and low dispersive spin waves in magnetic films (invited)

Theoretical description of spin wave (SW) envelope solitons in nonlinear dispersive media with dissipation is given in the framework of a nonlinear Schrodinger equation model with relaxation term. The conditions necessary for envelope soliton observation in magnetic films (MF) and film structures are formulated. Different types of SW dispersion laws are discussed in the context of envelope soliton formation. Formation of envelope solitons at microwave frequencies in periodic structures and in multilayered MF structures are predicted. Theoretically calculated parameters of envelope solitons of both highly dispersive and low dispersive SW in MF are compared to the results of experiments performed in thin yttrium-iron garnet (YIG) films. New experimental results showing the process of formation and propagation of envelope solitons of low dispersive dipolar SW in YIG films are presented.

Spin pinning and magnetic surface reconstruction; The effect on standing spin waves in films

We explore the effect of magnetic surface reconstruction on the spectrum of standing spin waves in magnetic films. We find that the surface spin instabilities produce effective pinning fields that depend strongly on magnetic field, temperature, and the strength of anisotropy fields in the surface.