Surface Acoustic Wave mediated magneto elastic investigation of magnetic thin film systems
Final Report Abstract
The aim of this project was to explore the magnetoacoustic interaction with high frequency surface acoustic waves (SAWs) giving rise to spin wave (SW) stimulation and influencing the magnetic reversal behavior. The studied devices consist of a piezoelectric substrate and interdigital transducers which are used for efficient excitation and detection of SAWs. A magnetic thin film is located in the propagation path of the SAWs. During the project, it turned out that the coupling between SAWs and SWs is nonreciprocal, which implies that the SAW transmission in magnitude and phase changes under an inversion of the SAW propagation direction. Thus, the focus of our project was to understand SAW-SW coupling phenomena and its nonreciprocity in various piezoelectric-ferromagnetic thin film heterostructures. On the one hand, we demonstrated that the pure magnetoacoustic excitation of SWs by SAWs is already nonreciprocal. The reason for this is the possible mismatch of the helicities of the magnetoacoustic driving field and magnetization dynamics. This effect is particularly pronounced in CoFeB(d) thin films due to magneto-rotational coupling and was also investigated for different SAW modes in thin Ni(10 nm) films. On the other hand, we demonstrated large nonreciprocal SAW transmission in ferromagnetic thinfilm systems which show a nonreciprocal SW dispersion. In particular, the SW dispersion of CoFeB(d: 1.4, …, 5 nm)/Pt(3 nm) bilayers is nonreciprocal due to the interfacial Dzyaloshinskii-Moriya interaction while the nonreciprocity of the dispersion in NiFe(20 nm)/Au(5 nm)/CoFeB(5 nm) is caused by interlayer magnetic-dipolar coupling. The combination of nonreciprocal magnetoacoustic excitation and nonreciprocal SW dispersion results in strongly nonreciprocal transmission characteristics for the fabricated piezoelectric-ferromagnetic hybrid structures. The pronounced nonreciprocal transmission of magnetoacoustic waves opens an avenue to build new types of miniaturized and energy-efficient microwave components, such as acoustic isolators or circulators. Furthermore, a phenomenological model was developed for the interpretation of the magnetoacoustic transmission measurements, which allows for the characterization of SWs and magnetic parameters of magnetic thin films. For instance, the thickness-averaged effective Dzyaloshinskii-Moriya constant can be determined. In addition, we have demonstrated magnetoacoustic excitation and characterization of SWs with micrometer-scale spatial resolution using specially designed “tapered” interdigital transducers. Finally, the symmetry of the magnetoelastic driving fields of Rayleigh and shear horizontal SAW modes allows to excite spin waves for any relative orientation of magnetization and SAW propagation direction and, moreover, can be utilized to characterize surface strain components of unknown acoustic wave modes.
Publications
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Surface acoustic wave mediated magneto elastic investigation of magnetic thin films, DPG Spring Meeting 2019 (31 März – 5 April 2019, Regensburg, Deutschland) – MA 15.40
M. Küß, M. Heigl, A. Hörner, M. Albrecht & A. Wixforth
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Nonreciprocal Dzyaloshinskii–Moriya Magnetoacoustic Waves. Physical Review Letters, 125(21).
Küß, M.; Heigl, M.; Flacke, L.; Hörner, A.; Weiler, M.; Albrecht, M. & Wixforth, A.
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Surface acoustic wave driven spin wave resonance spectroscopy, Mauterndorf 2020: 21st International Winter School on New Developments in Solid State Physics (23 – 28 Februar 2020, Mauterndorf, Österreich).
M. Küß, A. Hörner, M. Heigl, M. Albrecht & A. Wixforth
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Nonreciprocal magnetoacoustic surface waves in dipolar coupled ferromagnetic bilayers, The European Con- ference Physics of Magnetism 2021 (28 Juni – 2 Juli 2021, Poznań, Polen) – O-3-02.
Küß, M.; Heigl, M.; Flacke, L.; Hörner, A.; Weiler, M.; Wixforth, A. & Albrecht, M.
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Nonreciprocal Magnetoacoustic Waves in Dipolar-Coupled Ferromagnetic Bilayers. Physical Review Applied, 15(3).
Küß, M.; Heigl, M.; Flacke, L.; Hörner, A.; Weiler, M.; Wixforth, A. & Albrecht, M.
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Symmetry of the Magnetoelastic Interaction of Rayleigh and Shear Horizontal Magnetoacoustic Waves in Nickel Thin Films on LiTaO3. Physical Review Applied, 15(3).
Küß, M.; Heigl, M.; Flacke, L.; Hefele, A.; Hörner, A.; Weiler, M.; Albrecht, M. & Wixforth, A.
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Chiral Magnetoacoustics. Frontiers in Physics, 10.
Küß, Matthias; Albrecht, Manfred & Weiler, Mathias
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Forward volume magnetoacoustic spin wave excitation with micron-scale spatial resolution. APL Materials, 10(8).
Küß, M.; Porrati, F.; Hörner, A.; Weiler, M.; Albrecht, M.; Huth, M. & Wixforth, A.
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Nonreciprocal magnetoacoustic surface waves in a dipolar coupled ferromagnetic bilayer, 2022 Joint MMM-Intermag Conference (INTERMAG) (10 – 14 Januar 2022, New Orleans, USA) – HOJ-13
M. Küß
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Symmetry of the magnetoelastic interaction of Rayleigh and shear horizontal-magnetoacoustic waves, DPG Meeting 2022 (4 – 9 September 2022, Regensburg, Deutschland)
Küß, M.; Heigl, M.; Flacke, L.; Hefele, A.; Hörner, A.; Weiler, M.; Albrecht, M. & Wixforth, A.
