The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
I. Mertig - One of the best experts on this subject based on the ideXlab platform.
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Taking an electron-Magnon duality shortcut from electron to Magnon transport
Physical Review B, 2018Co-Authors: Alexander Mook, Jurgen Henk, Börge Göbel, I. MertigAbstract:The quasiparticles in insulating magnets are the charge-neutral Magnons, whose magnetic moments couple to electromagnetic fields. For collinear easy-axis magnets, this coupling can be mapped elegantly onto the scenario of charged particles in electromagnetic fields. From this mapping we obtain equations of motion for Magnon wave packets equal to those of electron wave packets in metals. Thus, well-established electronic transport phenomena can be carried over to Magnons: this duality shortcut facilitates the discussion of Magnon transport. We identify the Magnon versions of normal and anomalous Hall, Nernst, Ettingshausen, and Righi-Leduc effects. They are discussed for selected types of easy-axis magnets: ferromagnets, antiferromagnets, and ferrimagnets. Besides a Magnon Wiedemann-Franz law and the Magnon counterpart of the negative magnetoresistance of electrons in Weyl semimetals, we predict that certain low-symmetry ferrimagnets exhibit a nonlinear version of the anomalous Magnon Hall-effect family.
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Magnon nodal-line semimetals and drumhead surface states in anisotropic pyrochlore ferromagnets
Physical Review B, 2017Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:We introduce a type of topological Magnon matter: the Magnonic pendant to electronic nodal-line semimetals. Magnon spectra of anisotropic pyrochlore ferromagnets feature twofold degeneracies of Magnon bands along a closed loop in reciprocal space. These Magnon nodal lines are topologically protected by the coexistence of inversion and time-reversal symmetry; they require the absence of spin-orbit interaction (no Dzyaloshinskii-Moriya interaction). We calculate the topological invariants of the nodal lines and show that details of the associated Magnon drumhead surface states depend strongly on the termination of the surface. Magnon nodal-line semimetals complete the family of topological Magnons in three-dimensional ferromagnetic materials.
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Magnon waveguide with nanoscale confinement constructed from topological Magnon insulators
Physical Review B, 2015Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:Topological Magnon insulators host spatially confined edge Magnons brought about by the Dzyaloshinskii-Moriya interaction. Bringing two topological Magnon insulators into contact results in topologically protected unidirectional interface Magnons. These interface modes decay rapidly toward the bulk regions of the sample. As a result, heat and spin currents associated with these Magnons are as well unidirectional and strongly confined to a few-nanometer-wide strip along the interface. On top of this, these interface currents follow any geometry owing to the topological nature of the Magnons. In this theoretical study, we propose and analyze two recipes for composing Magnon waveguides with nanoscale confinement, one from topologically different phases, another from identical phases. We further identify material classes to construct these Magnon waveguides and propose an experiment to verify their topological nature.
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Edge states in topological Magnon insulators
Physical Review B - Condensed Matter and Materials Physics, 2014Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:For Magnons, the Dzyaloshinskii-Moriya interaction accounts for spin-orbit interaction and causes a nontrivial topology that allows for topological Magnon insulators. In this theoretical investigation we present the bulk-boundary correspondence for Magnonic kagome lattices by studying the edge Magnons calculated by a Green function renormalization technique. Our analysis explains the sign of the transverse thermal conductivity of the Magnon Hall effect in terms of topological edge modes and their propagation direction. The hybridization of topologically trivial with nontrivial edge modes enlarges the period in reciprocal space of the latter, which is explained by the topology of the involved modes.
Alexander Mook - One of the best experts on this subject based on the ideXlab platform.
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Taking an electron-Magnon duality shortcut from electron to Magnon transport
Physical Review B, 2018Co-Authors: Alexander Mook, Jurgen Henk, Börge Göbel, I. MertigAbstract:The quasiparticles in insulating magnets are the charge-neutral Magnons, whose magnetic moments couple to electromagnetic fields. For collinear easy-axis magnets, this coupling can be mapped elegantly onto the scenario of charged particles in electromagnetic fields. From this mapping we obtain equations of motion for Magnon wave packets equal to those of electron wave packets in metals. Thus, well-established electronic transport phenomena can be carried over to Magnons: this duality shortcut facilitates the discussion of Magnon transport. We identify the Magnon versions of normal and anomalous Hall, Nernst, Ettingshausen, and Righi-Leduc effects. They are discussed for selected types of easy-axis magnets: ferromagnets, antiferromagnets, and ferrimagnets. Besides a Magnon Wiedemann-Franz law and the Magnon counterpart of the negative magnetoresistance of electrons in Weyl semimetals, we predict that certain low-symmetry ferrimagnets exhibit a nonlinear version of the anomalous Magnon Hall-effect family.
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Magnon nodal-line semimetals and drumhead surface states in anisotropic pyrochlore ferromagnets
Physical Review B, 2017Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:We introduce a type of topological Magnon matter: the Magnonic pendant to electronic nodal-line semimetals. Magnon spectra of anisotropic pyrochlore ferromagnets feature twofold degeneracies of Magnon bands along a closed loop in reciprocal space. These Magnon nodal lines are topologically protected by the coexistence of inversion and time-reversal symmetry; they require the absence of spin-orbit interaction (no Dzyaloshinskii-Moriya interaction). We calculate the topological invariants of the nodal lines and show that details of the associated Magnon drumhead surface states depend strongly on the termination of the surface. Magnon nodal-line semimetals complete the family of topological Magnons in three-dimensional ferromagnetic materials.
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Magnon waveguide with nanoscale confinement constructed from topological Magnon insulators
Physical Review B, 2015Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:Topological Magnon insulators host spatially confined edge Magnons brought about by the Dzyaloshinskii-Moriya interaction. Bringing two topological Magnon insulators into contact results in topologically protected unidirectional interface Magnons. These interface modes decay rapidly toward the bulk regions of the sample. As a result, heat and spin currents associated with these Magnons are as well unidirectional and strongly confined to a few-nanometer-wide strip along the interface. On top of this, these interface currents follow any geometry owing to the topological nature of the Magnons. In this theoretical study, we propose and analyze two recipes for composing Magnon waveguides with nanoscale confinement, one from topologically different phases, another from identical phases. We further identify material classes to construct these Magnon waveguides and propose an experiment to verify their topological nature.
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Edge states in topological Magnon insulators
Physical Review B - Condensed Matter and Materials Physics, 2014Co-Authors: Alexander Mook, Jurgen Henk, I. MertigAbstract:For Magnons, the Dzyaloshinskii-Moriya interaction accounts for spin-orbit interaction and causes a nontrivial topology that allows for topological Magnon insulators. In this theoretical investigation we present the bulk-boundary correspondence for Magnonic kagome lattices by studying the edge Magnons calculated by a Green function renormalization technique. Our analysis explains the sign of the transverse thermal conductivity of the Magnon Hall effect in terms of topological edge modes and their propagation direction. The hybridization of topologically trivial with nontrivial edge modes enlarges the period in reciprocal space of the latter, which is explained by the topology of the involved modes.
Joseph P. Heremans - One of the best experts on this subject based on the ideXlab platform.
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effect of the Magnon dispersion on the longitudinal spin seebeck effect in yttrium iron garnets
Physical Review B, 2015Co-Authors: Hyungyu Jin, Stephen R Boona, Zihao Yang, R C Myers, Joseph P. HeremansAbstract:We study the temperature dependence of the longitudinal spin Seebeck effect (LSSE) in an yttrium iron garnet ${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (YIG)/Pt system for samples of different thicknesses. In this system, the thermal spin torque is Magnon driven. The LSSE signal peaks at a specific temperature that depends on the YIG sample thickness. We also observe freeze-out of the LSSE signal at high magnetic fields, which we attribute to the opening of an energy gap in the Magnon dispersion. We observe partial freeze-out of the LSSE signal even at room temperature, where ${k}_{B}T$ is much larger than the gap. This suggests that a subset of the Magnon population with an energy below ${k}_{B}{T}_{C} ({T}_{C}\ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ contributes disproportionately to the LSSE; at temperatures above ${T}_{C}$, we label these Magnons subthermal Magnons. The $T$ dependence of the LSSE at temperatures below the maximum is interpreted in terms of an empirical model that ascribes most of the temperature dependence to that of the thermally driven Magnon flux, which is related to the details of the Magnon dispersion.
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Magnon thermal mean free path in yttrium iron garnet
Physical Review B, 2014Co-Authors: Stephen R Boona, Joseph P. HeremansAbstract:The magnetothermal properties of monocrystalline yttrium iron garnet (YIG) are reported. The Magnon contribution to both the thermal conductivity and specific heat at low temperatures has been determined by measuring these properties under an applied magnetic field, which allows us to freeze the Magnon modes and isolate the phonon contribution relative to the zero-field behavior. These results are interpreted within the framework of a simple kinetic gas model for Magnon heat conduction that allows us to estimate the Magnon thermal mean free path, i.e., the inelastic scattering length scale for thermally driven bulk Magnons. We observe this parameter to reach as high as approximately 100 \ensuremath{\mu}m at 2 K. It tracks the acoustic phonon thermal mean free path closely and decreases rapidly as the temperature is increased. This relatively short length scale suggests that Magnon modes at thermal energies in YIG are not solely or directly responsible for coherent macroscale thermal spin transport (e.g., in the spin Seebeck effect) at high temperatures. Instead, these results support a growing consensus that subthermal Magnons, i.e., those at energies below about 30 \ifmmode\pm\else\textpm\fi{} 10 K, are important for spin transport in YIG at all temperatures. These results also emphasize that Magnon effects should be considered wavelength dependent, and that Magnon-Magnon interactions may be just as important for thermal spin transport as Magnon-phonon scattering. This, in turn, has implications for understanding the characteristic temperature and length scales involved in spin caloritronic phenomena.
Dan Stamperkurn - One of the best experts on this subject based on the ideXlab platform.
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condensing Magnons in a degenerate ferromagnetic spinor bose gas
Physical Review Letters, 2016Co-Authors: Fang Fang, Holger Kadau, Shun Wu, Dan StamperkurnAbstract:: We observe the quasicondensation of Magnon excitations within an F=1 ^{87}Rb spinor Bose-Einstein condensed gas. Magnons are pumped into a ferromagnetically ordered gas, allowed to equilibrate to a nondegenerate distribution, and then cooled evaporatively at near-constant net longitudinal magnetization, whereupon they condense. The critical Magnon number, spatial distribution, and momentum distribution indicate that Magnons condense in a potential that is uniform within the volume of the ferromagnetic condensate. The macroscopic transverse magnetization produced by the degenerate Magnon gas remains inhomogeneous within the ∼10 s equilibration time accessed in our experiment, and includes signatures of Mermin-Ho spin textures that appear as phase singularities in the Magnon quasicondensate wave function.
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condensing Magnons in a degenerate ferromagnetic spinor bose gas
Physical Review Letters, 2016Co-Authors: Fang Fang, Holger Kadau, Shun Wu, Dan StamperkurnAbstract:: We observe the quasicondensation of Magnon excitations within an F=1 ^{87}Rb spinor Bose-Einstein condensed gas. Magnons are pumped into a ferromagnetically ordered gas, allowed to equilibrate to a nondegenerate distribution, and then cooled evaporatively at near-constant net longitudinal magnetization, whereupon they condense. The critical Magnon number, spatial distribution, and momentum distribution indicate that Magnons condense in a potential that is uniform within the volume of the ferromagnetic condensate. The macroscopic transverse magnetization produced by the degenerate Magnon gas remains inhomogeneous within the ∼10 s equilibration time accessed in our experiment, and includes signatures of Mermin-Ho spin textures that appear as phase singularities in the Magnon quasicondensate wave function.
Vasily V. Temnov - One of the best experts on this subject based on the ideXlab platform.
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generation of exchange Magnons in thin ferromagnetic films by ultrashort acoustic pulses
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Valentin Besse, Anton V Golov, A Alekhin, L N Kotov, Igor V Bychkov, V. S. Vlasov, Dmitry A. Kuzmin, Vasily V. TemnovAbstract:Abstract We investigate generation of exchange Magnons by ultrashort, picosecond acoustic pulses propagating through ferromagnetic thin films. Using the Landau-Lifshitz-Gilbert equations we derive the dispersion relation for exchange Magnons for an external magnetic field tilted with respect to the film normal. Decomposing the solution in a series of standing spin wave modes, we derive a system of ordinary differential equations and driven harmonic oscillator equations describing the dynamics of individual Magnon mode. The external magnetoelastic driving force is given by the time-dependent spatial Fourier components of acoustic strain pulses inside the layer. Dependencies of the Magnon excitation efficiencies on the duration of the acoustic pulses and the external magnetic field highlight the role of acoustic bandwidth and phonon-Magnon phase matching. Our simulations for ferromagnetic nickel evidence the possibility of ultrafast magneto-acoustic excitation of exchange Magnons within the bandwidth of acoustic pulses in thin samples under conditions readily obtained in femtosecond pump-probe experiments.
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Generation of exchange Magnons in thin ferromagnetic films by ultrashort acoustic pulses
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Valentin Besse, Anton V Golov, A Alekhin, L N Kotov, Igor V Bychkov, V. S. Vlasov, D. Kuzmin, Vasily V. TemnovAbstract:We investigate generation of exchange Magnons by ultrashort, picosecond acoustic pulses propagating through ferromagnetic thin films. Using the Landau-Lifshitz-Gilbert equations we derive the dispersion relation for exchange Magnons for an external magnetic field tilted with respect to the film normal. Decomposing the solution in a series of standing spin wave modes, we derive a system of ordinary differential equations and driven harmonic oscillator equations describing the dynamics of individual Magnon mode. The external magnetoe-lastic driving force is given by the time-dependent spatial Fourier components of acoustic strain pulses inside the layer. Dependencies of the Magnon excita-tion efficiencies on the duration of the acoustic pulses and the external magnetic field highlight the role of acoustic bandwidth and phonon-Magnon phase matching. Our simulations for ferromagnetic nickel evidence the possibility of ultrafast magneto-acoustic excitation of exchange Magnons within the band-width of acoustic pulses in thin samples under conditions readily obtained in femtosecond pump-probe experiments. $ Fully documented templates are available in the elsarticle package on CTAN.