Experimental observation of magnetostatic wave envelope solitons in yttrium iron garnet films

Abstract

Formation of dipolar spin-wave (SW) (or magtietostatic wave) envelope solitons was observed in yttrium iron garnet films with unpinned surface spins under pulsed excitation. The solitons were formed in the spectral regions of relatively low dispersion from the short rectangular input pulses (T 4-50 ns). With the increase of the duration and/or amplitude of the input pulse, the multisoliton regime of SW propagation was registered. A theoretical interpretation of the observed nonlinear phenomena in terms of a nonlinear Schrodinger equation model with dissipation is given.(2tt/TV ) '(8'to/8k ') » to", I UI'»co, /(8to/8I UI'), (2) (3) where T is the duration of the in ut pulse, Vs 8at/8k is the wave group velocity, 8 co/8k is the wave dispersion, 8to/8IUI characterizes the wave nonlinearity, U is the dimensionless amplitude of the envelope of the propagating wave, and co"is the dissipation parameter of the propagating wave. For the case of spin-wave (SW) propagating in the ferromagnetic film (FF) the dimensionless amplitude of the SW envelope U is determined bywhere m",my are the components of the variable magnetization m and 4trMo (Mollz) is the equilibrium magnetization. The SW dissipation parameter is equal to to, 2try~k, where ) 2.8 MHz/Oe and AHk is the half-linewidth of ferromagnetic resonance in ferromagnetic film in Oe.It is worth noting that condition (3) in FF also means that the amplitude of the propagating SW should be greater than the threshold of the four-wave parametric decay process (second-order Suhl process ) toq+tol, =tot"+tot, "q;-(k;k) «k, i -1, 2, . . . , (5) which is responsible for the SW nonlinearity when the low-threshold three-wave decay processes (first-order Envelope solitons are stable nonlinear excitations that emerge during finite-amplitude wave pulse propagation in the dispersive media as a result of competition between the spreading effect of dispersion and the self-steepening effect of nonlinearity when both these effects are much stronger than the effect of dissipation. The conditions of envelope soliton formation in nonlinear dispersive media with dissipation are as follows:' (i) The Lighthill criterion which requires nonlinearity and dispersion to have opposite signs (8' N/8k')(8N/8 I UI') &0;(ii) the dissipation criteria that require the influence of dispersion and nonlinearity on the input pulse profile to be much greater than the influence of dissipation Suhl processes) COg COg, + Ng, (5a) are prohibited by conservation laws.There are two ways to satisfy the criterion (2): to find regions in the SW spectrum of the FF where dispersion 8 to/8k is sufficiently high, or to reduce the duration T of the input pulse when working in the spectral regions of relatively low dispersion.The first way was used in our work ' and led to the first experimental observation of dipole-exchange SW envelope solitons (T, 120 ns) in the regions of high dispersion near the dipole "gaps" in the dipole-exchange SW spectrum of a perpendicularly magnetized yttrium iron garnet (YIG) film with pinned sur...

Magnetic droplet solitons generated by pure spin currents

“…Dynamical magnetic envelope solitons, similar to the well-known temporal optical solitons [2], were observed about three decades ago in low-damping films of Yttrium Iron Garnet (YIG) [3,4], and have been intensively studied over the last years (see [5] and references therein). Because of the dynamic nature of these states, they are inhibited by the magnetic damping.…”

Magnonic crystals for data processing

“…This, in combination with a rich choice of linear and nonlinear spin-wave properties, makes spin waves excellent objects of study in general wave physics [8]. One-and two-dimensional soliton formation [15,16], nondiffractive spin-wave caustic beams [17][18][19], wave-front reversals [20,21], room-temperature Bose-Einstein condensation (BEC) of magnons [22,23], and formation of magnon supercurrents [24] are just a small selection of examples.…”

Magnon Spintronics

“…The propagation both of solitons and of two-dimensional nonlinear quasi-stable excitations called "bullets" (see Fig. 3), has been extensively studied in magnon systems [27][28][29][108][109][110]. The robustness of these waveforms gives them interesting potential as information bearers in magnon spintronic devices.…”