Interactions of Parametric Magnons in Ferromagnets
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Conditions for the appearance of the three, four, and five magnon fusions have been derived by Gottlieb and Suhl by making use of the dispersion relation of the spin wave, restricted to the Zeeman and exchange terms. In this paper we have determined these conditions of existence from the correct relations of dispersion containing the dipolar term neglected in the previous calculations. Experimental studies of the transient growth of parallel-pumped spin waves are in good agreement with these theoretical results, thus verifying that the parametric magnons are propagating perpendiculary to the dc magnetic field as predicted by the theory of Sparks and Kittel.Keywords:
Magnon
Dispersion relation
Spin wave
Spin-wave amplification techniques are key to the realization of magnon-based computing concepts. We introduce a novel mechanism to amplify spin waves in magnonic nanostructures. Using the technique of rapid cooling, we create a non-equilibrium state in excess of high-energy magnons and demonstrate the stimulated amplification of an externally seeded, propagating spin wave. Using an extended kinetic model, we qualitatively show that the amplification is mediated by an effective energy flux of high energy magnons into the low energy propagating mode, driven by a non-equilibrium magnon distribution.
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Energy flux
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Conditions for the appearance of the three, four, and five magnon fusions have been derived by Gottlieb and Suhl by making use of the dispersion relation of the spin wave, restricted to the Zeeman and exchange terms. In this paper we have determined these conditions of existence from the correct relations of dispersion containing the dipolar term neglected in the previous calculations. Experimental studies of the transient growth of parallel-pumped spin waves are in good agreement with these theoretical results, thus verifying that the parametric magnons are propagating perpendiculary to the dc magnetic field as predicted by the theory of Sparks and Kittel.
Magnon
Dispersion relation
Spin wave
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Dispersion relation
Spin wave
Surface States
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Determining the spin wave exchange constant of ferromagnets using canted high-order exchange magnons
We propose an alternative method for obtaining the spin wave exchange constant of a ferromagnetic material. This involves generating and detecting canted high-order magnons in Co films using a time-resolved magneto-optical Kerr effect instrument, which enables the extraction of the spin wave exchange constant in a single film thickness in a reliable manner. To enhance the sensitivity of high-order magnon detection, we perform simultaneous measurements of differential Kerr rotation and ellipticity on both sides of the film. This method will be particularly useful in practical situations where the magnetic properties of a material vary with thickness or where it is not feasible to produce films of the same quality.
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Constant (computer programming)
Magnonics
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The impact of the longitudinal spin Seebeck effect (LSSE) on the magnon damping in magnetic-insulator/nonmagnetic-metal bilayers was recently discussed in several reports. However, results of those experiments can be blurred by multimode excitation within the measured linewidth. In order to avoid possible intermodal interference, we investigated the damping of a single magnon group in a platinum covered yttrium iron garnet (YIG) film by measurement of the threshold of its parametric excitation. Both dipolar and exchange spin-wave branches were probed. It turned out that the LSSE-related modification of spin-wave damping in a micrometer-thick YIG film is too weak to be observed in the entire range of experimentally accessible wave vectors. At the same time, the change in the absolute temperature of the YIG layer, which can appear by applying a temperature gradient, strongly modifies the damping value.
Yttrium Iron Garnet
Magnon
Spin wave
Magnetic damping
Magnonics
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Spin-wave amplification techniques are key to the realization of magnon-based computing concepts. We introduce a novel mechanism to amplify spin waves in magnonic nanostructures. Using the technique of rapid cooling, we create a nonequilibrium state in excess of high-energy magnons and demonstrate the stimulated amplification of an externally seeded, propagating spin wave. Using an extended kinetic model, we qualitatively show that the amplification is mediated by an effective energy flux of high energy magnons into the low energy propagating mode, driven by a nonequilibrium magnon distribution.
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Spin wave
Realization (probability)
Energy flux
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It is predicted that in 2D magnonic crystals the edge rotational magnons of forward volume magnetostatic spin waves can exist. Under certain conditions, locally bounded magnons may appear within the crystal consisting of the ferromagnetic matrix and periodically inserted magnetic/non-magnetic inclusions. It is also shown that interplay of different resonances in 2D magnonic crystal may provide conditions for spin wave modes existence with negative group velocity.
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Crystal (programming language)
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We investigate giant magnons from classical rotating strings in two different backgrounds. First we generalize the solution of Hofman and Maldacena and investigate new magnon excitations of a spin chain which are dual to a string on $R\ifmmode\times\else\texttimes\fi{}{S}^{5}$ with two nonvanishing angular momenta. Allowing string dynamics along the third angle in the five sphere, we find a dispersion relation that reproduces the Hofman and Maldacena one and the one found by Dorey for the two spin case. In the second part of the paper we generalize the two ``spin'' giant magnon to the case of $\ensuremath{\beta}$-deformed ${\mathrm{AdS}}_{5}\ifmmode\times\else\texttimes\fi{}{S}^{5}$ background. We find agreement between the dispersion relation of the rotating string and the proposed dispersion relation of the magnon bound state on the spin chain.
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The magnetic excitations in ferromagnetic SrRuO$_3$ were studied by inelastic neutron scattering combining experiments on triple-axis and time-of-flight spectrometers with and without polarization analysis. A quadratic spin-wave dispersion with an anisotropy gap describes the low-energy low-temperature response. The magnon dispersion extends to at least 35 meV and there is no direct evidence for a continuum of Stoner excitations below this energy. However, the magnon response is weakened at higher energy. In addition to the anomalous softening of the spin-wave stiffness and of the gap, which is induced by the topology of the Bloch states, the magnon excitations are broadened in energy and this effect increases upon heating.
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Dispersion relation
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Spin-wave interactions in ferromagnetic insulators have a well-established theoretical foundation, in contrast to the situation for antiferromagnets. These interactions may be classified into two groups according to whether the dominant aspects are of one- or two-magnon character. The weak interactions between spin waves excited at low temperatures are responsible for the success of "free" (or noninteracting) spin-wave calculations in explaining low-temperature thermodynamic properties. In contrast, the two-magnon aspects appear in connection with two-magnon Raman scattering, where pairs of magnons are created in close proximity and consequently interact strongly. Parallels with analogous systems, especially antiferromagnetic spin waves and phonons, are noted in reviewing the ferromagnetic case. Emphasis is placed on the structure of the theory, rather than on the wealth of experimental activity.
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Heisenberg model
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