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Spin wave propagation in structures with locally modified magnetic anisotropy
Roučka, Václav ; Flajšman, Lukáš (oponent) ; Urbánek, Michal (vedoucí práce)
Devices based on spin waves have the potential to be used in low-power data processing. Naturally, a successful application would require many of those devices to be interconnected on a chip. Such a chip would have to include steering of spin waves through turned waveguides. The issue of steering dipole-exchange spin waves through waveguides has not been sufficiently solved so far, as the tested designs lead to a loss of intensity and phase coherence. In the presented thesis, we have studied two systems, which could be exploited for spin-wave steering. First, we dealt with metastable iron-nickel thin films. The paramagnetic metastable fcc layer epitaxially grown on a Cu substrate can be transformed into a stable ferromagnetic bcc phase by a focused ion beam. This technique gives us spatial control over the transformation process, and the scanning strategy even allows us to determine the direction of magnetic anisotropy. Magnetic properties of structures prepared by this technique, together with spin-wave refraction between domains with different anisotropy directions, were characterized by Brillouin light scattering microscopy. Moreover, we have studied spin-wave propagation in a system with corrugation induced magnetic anisotropy. The corrugated magnetic film is created by focused electron beam-induced deposition of nonmagnetic ridges on a substrate and subsequent deposition of the magnetic material. Turned corrugated waveguides of different designs were prepared and we have measured spin-wave propagation through them by Brillouin light scattering microscopy. Micromagnetic simulations were also employed to provide further insight and to help us identify good experimental designs.
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Phase-resolved Brillouin light scattering: development and applications
Wojewoda, Ondřej ; Dubroka, Adam (oponent) ; Urbánek, Michal (vedoucí práce)
Spin waves have the potential to be used as a new platform for data transfer and processing as they can reach wavelengths in the nanometer range and frequencies in the terahertz range. To be able to design the spin-wave devices and logic circuits we need to be able to gather the information about spatial distribution of the spin-wave intensity and if possible, also their phase. This can be measured with the use of phase-resolved micro-Brillouin-light-scattering (µ-BLS) setup. The presented work deals with extending the existing intensity resolved setup with the possibility to also acquire the spin-wave phase. The upgraded Brillouin light scattering setup is thoroughly described and its performance is characterized. The capabilities of the developed setup are demonstrated in the study of propagation of spin waves through a Néel domain wall. The acquired 2D spin-wave intensity maps reveal that spin-wave transmission through a domain wall is influenced by a topologically enforced circular Bloch line in the domain wall center and that the propagation regime depends on the spin-wave frequency. In the first regime, two spin-wave beams propagating around the circular Bloch line are formed, whereas in the second regime, spin waves propagate in a single central beam through the circular Bloch line. Phase-resolved µ-BLS measurements reveal a phase shift upon transmission through the domain wall for both regimes. Micromagnetic modelling of the transmitted spin waves unveils a distortion of their phase fronts which needs to be taken into account when interpreting the measurements and designing potential devices. Moreover, we show, by means of micromagnetic simulations, that an external magnetic field can be used to move the circular Bloch line within the domain wall to manipulate spin-wave propagation.
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Spin wave turns
Dočkalová, Lucie ; Gablech, Imrich (oponent) ; Urbánek, Michal (vedoucí práce)
In today's world of modern technology, there is considerable pressure to develop increasingly powerful electronic devices. These devices operate on the basis of integrated circuits, where the smallest components currently reach a size in the order of nanometers. Their further technological development connected with the trend of miniaturization encounters the limits resulting from the quantum character of electrons. Magnonics, as a new field of modern physics, offers a solution to this obstacle. Unlike electronic devices, magnonic devices process data using magnons, quasi-particles of spin waves. Although some magnonic devices have already been introduced, connecting them on a small chip is very complicated. Highly anisotropic dispersion relationships of spin waves prevent the efficient transmission of magnons through so-called waveguides. In this work, we deal with a way to overcome this anisotropy and thus allow the propagation of spin waves in any direction with the same efficiency. For this purpose, we use corrugated waveguides in the shape of bends, which we produce using a combination of electron lithography and deposition induced by a focused electron beam. The ripple of the prepared waveguides is characterized using an atomic force microscope. Subsequently, we examine the magnetic state of the structures using Kerr microscopy. Finally, we focus on the propagation of spin waves through the curves produced, which we measure using Brillouin light scattering spectroscopy.
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Studium propagace spinových vln v prostředí s netriviální distribucí magnetizace
Klíma, Jan ; Staňo, Michal (oponent) ; Wojewoda, Ondřej (vedoucí práce)
Magnonika je obor fyziky zabývající se spinovými vlnami a jejich kvazičásticemi – magnony. Spinové vlny jsou jedním z kandidátů pro budoucí výpočetní technologie. Obvody a součástky využívající vlastnosti spinových vln mají potenciál doplnit či nahradit ty současné, založené na CMOS technologiích, které již dosáhly svého fyzikálního limitu. Pro zpracování informací pomocí spinových vln je zapotřebí umět spinové vlny efektivně navádět v magnonických obvodech, zejména v různě zahnutých vlnovodech propojujících jednotlivé prvky obvodů. Kvůli anizotropnímu chování spinových vln není tato problematika zcela triviální a dosud nebyla dostatečně prozkoumána. V této práci jsme využili zvlnění magnetické vrstvy vlnovodu, které indukuje uniaxiální magnetickou anizotropii, s jejíž pomocí můžeme efektivně ovládat směr magnetizace ve vlnovodu s prostorovým rozlišením v řádu desetin mikrometru. Tímto způsobem můžeme šířit spinové vlny v požadovaných módech v různých směrech bez nutnosti vnějšího pole. K návrhu zatáčky jsme vytvořili model, který analyzuje energetické příspěvky magnetizace a najde tak velikost a směr výsledného efektivního magnetického pole. Pomocí tohoto modelu a důkladné analýzy disperzní relace jsme navrhli zahnutý vlnovod, který je schopný stočit spinové vlny, což jsme prokázali mikroskopií Brillouinova rozptylu světla.
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Spin wave turns
Dočkalová, Lucie ; Gablech, Imrich (oponent) ; Urbánek, Michal (vedoucí práce)
In today's world of modern technology, there is considerable pressure to develop increasingly powerful electronic devices. These devices operate on the basis of integrated circuits, where the smallest components currently reach a size in the order of nanometers. Their further technological development connected with the trend of miniaturization encounters the limits resulting from the quantum character of electrons. Magnonics, as a new field of modern physics, offers a solution to this obstacle. Unlike electronic devices, magnonic devices process data using magnons, quasi-particles of spin waves. Although some magnonic devices have already been introduced, connecting them on a small chip is very complicated. Highly anisotropic dispersion relationships of spin waves prevent the efficient transmission of magnons through so-called waveguides. In this work, we deal with a way to overcome this anisotropy and thus allow the propagation of spin waves in any direction with the same efficiency. For this purpose, we use corrugated waveguides in the shape of bends, which we produce using a combination of electron lithography and deposition induced by a focused electron beam. The ripple of the prepared waveguides is characterized using an atomic force microscope. Subsequently, we examine the magnetic state of the structures using Kerr microscopy. Finally, we focus on the propagation of spin waves through the curves produced, which we measure using Brillouin light scattering spectroscopy.
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Spin wave propagation in structures with locally modified magnetic anisotropy
Roučka, Václav ; Flajšman, Lukáš (oponent) ; Urbánek, Michal (vedoucí práce)
Devices based on spin waves have the potential to be used in low-power data processing. Naturally, a successful application would require many of those devices to be interconnected on a chip. Such a chip would have to include steering of spin waves through turned waveguides. The issue of steering dipole-exchange spin waves through waveguides has not been sufficiently solved so far, as the tested designs lead to a loss of intensity and phase coherence. In the presented thesis, we have studied two systems, which could be exploited for spin-wave steering. First, we dealt with metastable iron-nickel thin films. The paramagnetic metastable fcc layer epitaxially grown on a Cu substrate can be transformed into a stable ferromagnetic bcc phase by a focused ion beam. This technique gives us spatial control over the transformation process, and the scanning strategy even allows us to determine the direction of magnetic anisotropy. Magnetic properties of structures prepared by this technique, together with spin-wave refraction between domains with different anisotropy directions, were characterized by Brillouin light scattering microscopy. Moreover, we have studied spin-wave propagation in a system with corrugation induced magnetic anisotropy. The corrugated magnetic film is created by focused electron beam-induced deposition of nonmagnetic ridges on a substrate and subsequent deposition of the magnetic material. Turned corrugated waveguides of different designs were prepared and we have measured spin-wave propagation through them by Brillouin light scattering microscopy. Micromagnetic simulations were also employed to provide further insight and to help us identify good experimental designs.
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Phase-resolved Brillouin light scattering: development and applications
Wojewoda, Ondřej ; Dubroka, Adam (oponent) ; Urbánek, Michal (vedoucí práce)
Spin waves have the potential to be used as a new platform for data transfer and processing as they can reach wavelengths in the nanometer range and frequencies in the terahertz range. To be able to design the spin-wave devices and logic circuits we need to be able to gather the information about spatial distribution of the spin-wave intensity and if possible, also their phase. This can be measured with the use of phase-resolved micro-Brillouin-light-scattering (µ-BLS) setup. The presented work deals with extending the existing intensity resolved setup with the possibility to also acquire the spin-wave phase. The upgraded Brillouin light scattering setup is thoroughly described and its performance is characterized. The capabilities of the developed setup are demonstrated in the study of propagation of spin waves through a Néel domain wall. The acquired 2D spin-wave intensity maps reveal that spin-wave transmission through a domain wall is influenced by a topologically enforced circular Bloch line in the domain wall center and that the propagation regime depends on the spin-wave frequency. In the first regime, two spin-wave beams propagating around the circular Bloch line are formed, whereas in the second regime, spin waves propagate in a single central beam through the circular Bloch line. Phase-resolved µ-BLS measurements reveal a phase shift upon transmission through the domain wall for both regimes. Micromagnetic modelling of the transmitted spin waves unveils a distortion of their phase fronts which needs to be taken into account when interpreting the measurements and designing potential devices. Moreover, we show, by means of micromagnetic simulations, that an external magnetic field can be used to move the circular Bloch line within the domain wall to manipulate spin-wave propagation.
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