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Gallardo R, Weigand M, Schultheiss K, Kakay A, Mattheis R, Raabe J, Schütz G, Deac A, Lindner J, Wintz S. Coherent Magnons with Giant Nonreciprocity at Nanoscale Wavelengths. ACS NANO 2024. [PMID: 38314709 PMCID: PMC10883124 DOI: 10.1021/acsnano.3c08390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
Nonreciprocal wave propagation arises in systems with broken time-reversal symmetry and is key to the functionality of devices, such as isolators or circulators, in microwave, photonic, and acoustic applications. In magnetic systems, collective wave excitations known as magnon quasiparticles have so far yielded moderate nonreciprocities, mainly observed by means of incoherent thermal magnon spectra, while their occurrence as coherent spin waves (magnon ensembles with identical phase) is yet to be demonstrated. Here, we report the direct observation of strongly nonreciprocal propagating coherent spin waves in a patterned element of a ferromagnetic bilayer stack with antiparallel magnetic orientations. We use time-resolved scanning transmission X-ray microscopy (TR-STXM) to directly image the layer-collective dynamics of spin waves with wavelengths ranging from 5 μm down to 100 nm emergent at frequencies between 500 MHz and 5 GHz. The experimentally observed nonreciprocity factor of these counter-propagating waves is greater than 10 with respect to both group velocities and specific wavelengths. Our experimental findings are supported by the results from an analytic theory, and their peculiarities are further discussed in terms of caustic spin-wave focusing.
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Affiliation(s)
- Rodolfo Gallardo
- Universidad Técnica Federico Santa María, 2390123 Valparaíso, Chile
| | | | - Katrin Schultheiss
- Helmholtz-Zentrum Dresden-Rossendorf, Insitute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
| | - Attila Kakay
- Helmholtz-Zentrum Dresden-Rossendorf, Insitute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
| | - Roland Mattheis
- Leibniz Institut für Photonische Technologien, 07745 Jena, Germany
| | - Jörg Raabe
- Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Gisela Schütz
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
| | - Alina Deac
- Helmholtz-Zentrum Dresden-Rossendorf, Dresden High Magnetic Field Laboratory, 01328 Dresden, Germany
| | - Jürgen Lindner
- Helmholtz-Zentrum Dresden-Rossendorf, Insitute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany
| | - Sebastian Wintz
- Helmholtz-Zentrum Berlin, 12489 Berlin, Germany
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
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Schulz F, Litzius K, Powalla L, Birch MT, Gallardo RA, Satheesh S, Weigand M, Scholz T, Lotsch BV, Schütz G, Burghard M, Wintz S. Direct Observation of Propagating Spin Waves in the 2D van der Waals Ferromagnet Fe 5GeTe 2. NANO LETTERS 2023; 23:10126-10131. [PMID: 37955345 PMCID: PMC10683057 DOI: 10.1021/acs.nanolett.3c02212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 11/01/2023] [Accepted: 11/03/2023] [Indexed: 11/14/2023]
Abstract
Magnetism in reduced dimensionalities is of great fundamental interest while also providing perspectives for applications of materials with novel functionalities. In particular, spin dynamics in two dimensions (2D) have become a focus of recent research. Here, we report the observation of coherent propagating spin-wave dynamics in a ∼30 nm thick flake of 2D van der Waals ferromagnet Fe5GeTe2 using X-ray microscopy. Both phase and amplitude information were obtained by direct imaging below TC for frequencies from 2.77 to 3.84 GHz, and the corresponding spin-wave wavelengths were measured to be between 1.5 and 0.5 μm. Thus, parts of the magnonic dispersion relation were determined despite a relatively high magnetic damping of the material. Numerically solving an analytic multilayer model allowed us to corroborate the experimental dispersion relation and predict the influence of changes in the saturation magnetization or interlayer coupling, which could be exploited in future applications by temperature control or stacking of 2D-heterostructures.
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Affiliation(s)
- Frank Schulz
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Kai Litzius
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
- Universität
Augsburg, D-86159 Augsburg, Germany
| | - Lukas Powalla
- Max
Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Max T. Birch
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
- RIKEN
Center for Emergent Matter Science, JP-351-0198 Wako, Japan
| | - Rodolfo A. Gallardo
- Universidad
Técnica Federico Santa María, Avenida España 1680, 2390123 Valparaiso, Chile
| | - Sayooj Satheesh
- Max
Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Markus Weigand
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
- Helmholtz-Zentrum
Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
| | - Tanja Scholz
- Max
Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Bettina V. Lotsch
- Max
Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Gisela Schütz
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
| | - Marko Burghard
- Max
Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany
| | - Sebastian Wintz
- Max
Planck Institute for Intelligent Systems, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
- Helmholtz-Zentrum
Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany
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Gerlinger K, Pfau B, Hennecke M, Kern LM, Will I, Noll T, Weigand M, Gräfe J, Träger N, Schneider M, Günther CM, Engel D, Schütz G, Eisebitt S. Pump-probe x-ray microscopy of photo-induced magnetization dynamics at MHz repetition rates. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2023; 10:024301. [PMID: 36970496 PMCID: PMC10038236 DOI: 10.1063/4.0000167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 02/16/2023] [Indexed: 06/18/2023]
Abstract
We present time-resolved scanning x-ray microscopy measurements with picosecond photo-excitation via a tailored infrared pump laser at a scanning transmission x-ray microscope. Specifically, we image the laser-induced demagnetization and remagnetization of thin ferrimagnetic GdFe films proceeding on a few nanoseconds timescale. Controlling the heat load on the sample via additional reflector and heatsink layers allows us to conduct destruction-free measurements at a repetition rate of 50 MHz. Near-field enhancement of the photo-excitation and controlled annealing effects lead to laterally heterogeneous magnetization dynamics which we trace with 30 nm spatial resolution. Our work opens new opportunities to study photo-induced dynamics on the nanometer scale, with access to picosecond to nanosecond time scales, which is of technological relevance, especially in the field of magnetism.
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Affiliation(s)
- Kathinka Gerlinger
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Bastian Pfau
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Martin Hennecke
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Lisa-Marie Kern
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Ingo Will
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Tino Noll
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Markus Weigand
- Helmholtz-Zentrum Berlin für Materialien und Energie, 12489 Berlin, Germany
| | - Joachim Gräfe
- Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
| | - Nick Träger
- Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
| | - Michael Schneider
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Christian M. Günther
- Technische Universität Berlin, Zentraleinrichtung Elektronenmikroskopie (ZELMI), 10623 Berlin, Germany
| | - Dieter Engel
- Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Gisela Schütz
- Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
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Feggeler T, Meckenstock R, Spoddig D, Schöppner C, Zingsem B, Schaffers T, Ohldag H, Wende H, Farle M, Ney A, Ollefs K. Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure. Sci Rep 2022; 12:18724. [PMID: 36333578 PMCID: PMC9636384 DOI: 10.1038/s41598-022-23273-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Accepted: 10/27/2022] [Indexed: 11/06/2022] Open
Abstract
We present the element-specific and time resolved visualization of uniform ferromagnetic resonance excitations of a Permalloy (Py) disk–Cobalt (Co) stripe bilayer microstructure. The transverse high frequency component of the resonantly excited magnetization is sampled in the ps regime by a combination of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy (STXM-FMR) recording snapshots of the local magnetization precession of Py and Co with nanometer spatial resolution. The approach allows us to individually image the resonant dynamic response of each element, and we find that angular momentum is transferred from the Py disk to the Co stripe and vice versa at their respective resonances. The integral (cavity) FMR spectrum of our sample shows an unexpected additional third resonance. This resonance is observed in the STXM-FMR experiments as well. Our microscopic findings suggest that it is governed by magnetic exchange between Py and Co, showing for the Co stripe a difference in relative phase of the magnetization due to stray field influence.
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