The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Gerrit E W Bauer - One of the best experts on this subject based on the ideXlab platform.
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chiral coupling of Magnons in waveguides
Physical Review B, 2020Co-Authors: Tao Yu, Sanchar Sharma, Ya M Blanter, Xiang Zhang, Gerrit E W BauerAbstract:We theoretically investigate the collective excitations of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnon-photon coupling can be tuned to be chiral, i.e., Magnons only couple with photons propagating in one direction, leading to an asymmetric transfer of angular momentum and energy between the magnets. A large enhancement of the magnon number population can be achieved at an edge of a long chain of magnets. The chain also supports standing waves with low radiation efficiency that are inert to the chirality.
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coherent pumping of high momentum Magnons by light
Physical Review B, 2020Co-Authors: Fran Simic, Sanchar Sharma, Ya M Blanter, Gerrit E W BauerAbstract:We propose and model a method to excite a large number of coherent Magnons with high momentum in optical cavities. This is achieved by two counterpropagating optical modes that are detuned by the frequency of a selected magnon, similar to stimulated Raman scattering. In submillimeter-size yttrium iron garnet spheres, a milliwatt laser input power generates 106-108 coherent Magnons. The large magnon population enhances Brillouin light scattering, a probe suitable to access their quantum properties.
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coherent pumping of high momentum Magnons by light
arXiv: Mesoscale and Nanoscale Physics, 2019Co-Authors: Fran Simic, Sanchar Sharma, Ya M Blanter, Gerrit E W BauerAbstract:We propose to excite a large number of coherent Magnons with high momentum in optical cavities. This is achieved by two counterpropagating optical modes that are detuned by the frequency of a selected magnon, similar to stimulated Raman scattering. In sub-mm size yttrium iron garnet spheres, a mW laser input power generates 10^6-10^8 coherent Magnons. The large magnon population enhances Brillouin light scattering, a probe suitable to access their quantum properties.
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chiral coupling of Magnons in waveguides
arXiv: Mesoscale and Nanoscale Physics, 2019Co-Authors: Tao Yu, Sanchar Sharma, Ya M Blanter, Xiang Zhang, Gerrit E W BauerAbstract:We theoretically investigate the collective excitation of multiple (sub)millimeter-sized ferromagnets mediated by waveguide photons. By the position of the magnets in the waveguide, the magnon-photon coupling can be tuned to be chiral, i.e., Magnons only couple with photons propagating in one direction, leading to asymmetric transfer of angular momentum and energy between the magnets. A large imbalance in the magnon number distribution over the magnets can be achieved with a long chain of magnets, which concentrate at one edge. The chain also supports standing waves with low radiation efficiency that is inert to the chirality.
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optical cooling of Magnons
Physical Review Letters, 2018Co-Authors: Sanchar Sharma, Ya M Blanter, Gerrit E W BauerAbstract:: Inelastic scattering of light by spin waves generates an energy flow between the light and magnetization fields, a process that can be enhanced and controlled by concentrating the light in magneto-optical resonators. Here, we model the cooling of a sphere made of a magnetic insulator, such as yttrium iron garnet, using a monochromatic laser source. When the magnon lifetimes are much larger than the optical ones, we can treat the latter as a Markovian bath for Magnons. The steady-state Magnons are canonically distributed with a temperature that is controlled by the light intensity. We predict that such a cooling process can significantly reduce the temperature of the magnetic order within current technology.
R A Duine - One of the best experts on this subject based on the ideXlab platform.
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antiferromagnetic Magnons as highly squeezed fock states underlying quantum correlations
Physical Review B, 2019Co-Authors: Akashdeep Kamra, R A Duine, Even Thingstad, Gianluca Rastelli, Arne Brataas, Wolfgang Belzig, Asle SudboAbstract:Employing the concept of two-mode squeezed states from quantum optics, we demonstrate a revealing physical picture for the antiferromagnetic ground state and excitations. Superimposed on a Neel ordered configuration, a spin-flip restricted to one of the sublattices is called a sublattice magnon. We show that an antiferromagnetic spin-up magnon is composed of a quantum superposition of states with n+1 spin-up and n spin-down sublattice Magnons and is thus an enormous excitation despite its unit net spin. Consequently, its large sublattice spin can amplify its coupling to other excitations. Employing von Neumann entropy as a measure, we show that the antiferromagnetic eigenmodes manifest a high degree of entanglement between the two sublattices, thereby establishing antiferromagnets as reservoirs for strong quantum correlations. Based on these insights, we outline strategies for exploiting the strong quantum character of antiferromagnetic (squeezed) Magnons and give an intuitive explanation for recent experimental and theoretical findings in antiferromagnetic magnon spintronics.
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influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited Magnons
Physical Review B, 2016Co-Authors: Juan Shan, L. J. Cornelissen, N Vlietstra, Jamal Ben Youssef, Timo Kuschel, R A Duine, Bart J Van WeesAbstract:We studied the nonlocal transport behavior of both electrically and thermally excited Magnons in yttrium iron garnet (YIG) as a function of its thickness. For electrically injected Magnons, the nonlocal signals decrease monotonically as the YIG thickness increases. For the nonlocal behavior of the thermally generated Magnons, or the nonlocal spin Seebeck effect (SSE), we observed a sign reversal which occurs at a certain heater-detector distance, and it is influenced by both the opacity of the YIG/heater interface and the YIG thickness. Our nonlocal SSE results can be qualitatively explained by the bulk-driven SSE mechanism together with the magnon diffusion model. Using a two-dimensional finite element model (2D-FEM), we estimated the bulk spin Seebeck coefficient of YIG at room temperature. The quantitative disagreement between the experimental and modeled results indicates more complex processes going on in addition to magnon diffusion and relaxation, especially close to the contacts.
J Kirschner - One of the best experts on this subject based on the ideXlab platform.
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long living terahertz Magnons in ultrathin metallic ferromagnets
Nature Communications, 2015Co-Authors: Kh Zakeri, A Ernst, L M Sandratskii, Pawel Buczek, Alberto Marmodoro, T H Chuang, Y Zhang, J KirschnerAbstract:The technological application of ultrafast terahertz Magnons in itinerant ferromagnetic nanostructures is currently limited by magnon relaxation due to Landau damping. Here, Qin et al. demonstrate suppressed Landau damping and enhanced magnon lifetimes in ultrathin films of Fe–Pd alloy.
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Magnons in ultrathin ferromagnetic films with a large perpendicular magnetic anisotropy
Physical Review B, 2013Co-Authors: Kh Zakeri, A Ernst, T H Chuang, J Kirschner, Y J Chen, Y MengAbstract:We report on an experimental observation of high-energy magnon excitations in ultrathin ferromagnetic films with a perpendicular easy axis. We demonstrate that a transversally spin-polarized beam can be used to excite and probe the high-energy Magnons within spin-polarized electron energy-loss spectroscopy experiments. The magnon dispersion relation and lifetime are probed over the entire surface Brillouin zone for a set of body-centered tetragonal FeCo films with a large perpendicular magnetic anisotropy. First-principles calculations reveal that in addition to the tetragonal distortion, which is the origin of the large perpendicular magnetic anisotropy, the interfacial electronic hybridization also has a considerable impact on the properties of Magnons.
Burkard Hillebrands - One of the best experts on this subject based on the ideXlab platform.
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Stimulated thermalization of a parametrically driven magnon gas as a prerequisite for Bose-Einstein magnon condensation
Physical Review B, 2015Co-Authors: P. Clausen, Burkard Hillebrands, Dmytro A. Bozhko, Vitaliy I. Vasyuchka, G. A. Melkov, Alexander A. SergaAbstract:Faculty of Radiophysics, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine(Dated: March 2, 2015)Thermalization of a parametrically driven magnon gas leading to the formation of a Bose-Einstein conden-sate at the bottom of a spin-wave spectrum was studied by time- and wavevector-resolved Brillouin light scat-tering spectroscopy. It has been found that the condensation is preceded by the conversion of initially pumpedMagnons into a second group of frequency degenerated Magnons, which appear due to parametrically stimulatedscattering of the initial Magnons to a short-wavelength spectral region. In contrast to the first magnon group,which wavevectors are orthogonal to the wavevectors of the Magnons at the lowest energy states, the secondaryMagnons can effectively scatter to the bottom of the spectrum and condense there.
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Magnon Supercurrent in a Magnon Bose-Einstein Condensate subject to a Thermal Gradient
2015Co-Authors: P. Clausen, Burkard HillebrandsAbstract:We report evidence for the existence of a supercurrent of Magnons in a magnon Bose-Einstein condensate (BEC) prepared in a room temperature yttrium-iron-garnet (YIG) magnetic film. The magnon BEC is formed in a parametrically populated magnon gas, and its temporal evolution is studied by time-resolved Brillouin light scattering (BLS) spectroscopy in the area of the BLS laser focus. It has been found that local laser heating in the center of the condensate decreases the density of the magnon BEC in the steady-state pump regime and it enhances the temporal decrease of the freely evolving magnon condensate after the termination of the pumping pulse, but it does not alter the relaxation dynamics of the gaseous magnon phase. This phenomenon is understood as the appearance of a magnon supercurrent within the condensate due to a temperature-gradient induced phase gradient in the condensate. Bose-Einstein condensation [1] can be achieved either by decreasing the temperature of a boson gas [2] or by increasing its density. The latter method is especially applicable to g ases of weakly interacting quasi-particles such as excitons [3] , polaritons [4, 5], photons [6], and Magnons [7, 8]. When a spin system is pumped, and when the injected Magnons thermalize through scattering processes conserving both their number and the total energy, a Bose-Einstein condensate (BEC) may be formed at the lowest energy state of the energy-momentum spectrum even at room temperature conditions of the magnetic film carrying the Magnons [8, 9]. As the condensed magnon phase is localized in the global energy minimum, its group velocity is exactly zero and no energy transport can be associated with the magnon BEC. The situation can change, when a magnon supercurrent driven by a gradient in the phase of the wavefunction of a magnon condensate can be excited. Such a phase gradient can be induced by, e.g., a potential gradient or a temperature gradient. However, the dynamics of magnon condensates in such a gradient is still terra incognita. Here we provide experimental insight into the evolution of a magnon BEC in a thermal gradient generated by local laser heating. We show that such a heating influences both the steady-state characteristics and the transitional behavior of the magno n BEC, which can be understood using the concept of a magnon supercurrent. We study the temporal evolution of a magnon BEC in a single-crystal yttrium iron garnet (YIG, Y3Fe5O12) film by
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Magnon transistor for all-magnon data processing
Nature Communications, 2014Co-Authors: A. V. Chumak, A. A. Serga, Burkard HillebrandsAbstract:An attractive direction in next-generation information processing is the development of systems employing particles or quasiparticles other than electrons—ideally with low dissipation—as information carriers. One such candidate is the magnon: the quasiparticle associated with the eigen-excitations of magnetic materials known as spin waves. The realization of single-chip all-magnon information systems demands the development of circuits in which magnon currents can be manipulated by Magnons themselves. Using a magnonic crystal—an artificial magnetic material—to enhance nonlinear magnon–magnon interactions, we have succeeded in the realization of magnon-by-magnon control, and the development of a magnon transistor. We present a proof of concept three-terminal device fabricated from an electrically insulating magnetic material. We demonstrate that the density of Magnons flowing from the transistor’s source to its drain can be decreased three orders of magnitude by the injection of Magnons into the transistor’s gate.
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brillouin light scattering spectroscopy of parametrically excited dipole exchange Magnons
Physical Review B, 2012Co-Authors: A. A. Serga, Burkard Hillebrands, C W Sandweg, V I Vasyuchka, Matthias B Jungfleisch, Andreas Kreisel, Peter Kopietz, Mikhail KostylevAbstract:The spectral distribution of parametrically excited dipole-exchange Magnons in an in-plane magnetized epitaxial film of yttrium-iron garnet was studied by means of frequency- and wavevector-resolved Brillouin light scattering spectroscopy. The experiment was performed in a parallel pumping geometry where an exciting microwave magnetic field was parallel to the magnetizing field. It was found that for both dipolar and exchange spectral areas parallel pumping excites the lowest volume magnon modes propagating in the film plane perpendicularly to the magnetization direction. In order to interpret the experimental observations, we used a microscopic Heisenberg model that includes exchange as well as dipole-dipole interactions to calculate the magnon spectrum and construct the eigenstates. As proven in our calculations, the observed Magnons are characterized by having the highest possible ellipticity of precession which suggests the lowest threshold of parametric generation. Applying different pumping powers we observe modifications in the magnon spectrum that are described theoretically by a softening of the spin stiffness.
Ran Cheng - One of the best experts on this subject based on the ideXlab platform.
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birefringence like spin transport via linearly polarized antiferromagnetic Magnons
Nature Nanotechnology, 2020Co-Authors: Pengxiang Zhang, Zhen Bi, Taqiyyah Safi, Junxiang Xiang, Joseph Finley, Liang Fu, Ran ChengAbstract:Antiferromagnets (AFMs) possess great potential in spintronics because of their immunity to external magnetic disturbance, the absence of a stray field or the resonance in the terahertz range1,2. The coupling of insulating AFMs to spin–orbit materials3–7 enables spin transport via AFM Magnons. In particular, spin transmission over several micrometres occurs in some AFMs with easy-axis anisotropy8,9. Easy-plane AFMs with two orthogonal, linearly polarized magnon eigenmodes own unique advantages for low-energy control of ultrafast magnetic dynamics2. However, it is commonly conceived that these magnon modes are less likely to transmit spins because of their vanishing angular momentum9–11. Here we report experimental evidence that an easy-plane insulating AFM, an α-Fe2O3 thin film, can efficiently transmit spins over micrometre distances. The spin decay length shows an unconventional temperature dependence that cannot be captured considering solely thermal magnon scatterings. We interpret our observations in terms of an interference of two linearly polarized, propagating Magnons in analogy to the birefringence effect in optics. Furthermore, our devices can realize a bi-stable spin-current switch with a 100% on/off ratio under zero remnant magnetic field. These findings provide additional tools for non-volatile, low-field control of spin transport in AFM systems. Easy-plane antiferromagnet materials promise low-energy control of ultrafast magnetic dynamics in future spintronics applications, but host Magnons with vanishing angular momentum, which makes spin transport via Magnons unlikely. Through interference of two linearly polarized propagating Magnons, spin transport over micrometre distances is yet possible.
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spin current from sub terahertz generated antiferromagnetic Magnons
Nature, 2020Co-Authors: Junxue Li, Ran Cheng, Blake C Wilson, Mark Lohmann, Marzieh Kavand, Wei Yuan, Mohammed Aldosary, N I Agladze, M S SherwinAbstract:Spin dynamics in antiferromagnets has much shorter timescales than in ferromagnets, offering attractive properties for potential applications in ultrafast devices1–3. However, spin-current generation via antiferromagnetic resonance and simultaneous electrical detection by the inverse spin Hall effect in heavy metals have not yet been explicitly demonstrated4–6. Here we report sub-terahertz spin pumping in heterostructures of a uniaxial antiferromagnetic Cr2O3 crystal and a heavy metal (Pt or Ta in its β phase). At 0.240 terahertz, the antiferromagnetic resonance in Cr2O3 occurs at about 2.7 tesla, which excites only right-handed Magnons. In the spin-canting state, another resonance occurs at 10.5 tesla from the precession of induced magnetic moments. Both resonances generate pure spin currents in the heterostructures, which are detected by the heavy metal as peaks or dips in the open-circuit voltage. The pure-spin-current nature of the electrically detected signals is unambiguously confirmed by the reversal of the voltage polarity observed under two conditions: when switching the detector metal from Pt to Ta, reversing the sign of the spin Hall angle7–9, and when flipping the magnetic-field direction, reversing the magnon chirality4,5. The temperature dependence of the electrical signals at both resonances suggests that the spin current contains both coherent and incoherent magnon contributions, which is further confirmed by measurements of the spin Seebeck effect and is well described by a phenomenological theory. These findings reveal the unique characteristics of magnon excitations in antiferromagnets and their distinctive roles in spin–charge conversion in the high-frequency regime. Pure spin currents are simultaneously generated and detected electrically through sub-terahertz Magnons in the antiferromagnetic insulator Cr2O3, demonstrating the potential of magnon excitations in antiferromagnets for high-frequency spintronic devices.
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interlayer couplings mediated by antiferromagnetic Magnons
Physical Review Letters, 2018Co-Authors: Ran Cheng, Di XiaoAbstract:Author(s): Cheng, Ran; Xiao, Di; Zhu, Jian-Gang | Abstract: Collinear antiferromagnets (AFs) support two degenerate magnon excitations carrying opposite spin polarizations, by which Magnons can function as electrons in various spin-related phenomena. In an insulating ferromagnet(F)/AF/F trilayer, we explore the magnon-mediated interlayer coupling by calculating the magnon thermal energy in the AF as a function of the orientations of the Fs. The effect manifests as an interlayer exchange interaction and a perpendicular magnetic anisotropy; they both depend on temperature and the AF thickness. In particular, the exchange interaction turns out to be antiferromagnetic at low temperatures and ferromagnetic at high temperatures, whose magnitude can be 10-100 μeV for nanoscale separations, allowing experimental verification.
