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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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Static and dynamic properties of nanostructured magnetic materials
Vaňatka, Marek ; Wintz, Sebastian (oponent) ; Dijken, Sebastiaan van (oponent) ; Urbánek, Michal (vedoucí práce)
During the last years, magnetic materials and nanostructures have been intensively studied for their applications in recording media and logic circuits. This work follows our ongoing research in this field and mainly focuses on the static and dynamic properties of nanostructured materials, e.g., NiFe, CoFeB, and YIG. The thesis starts with a theoretical introduction showing the basic description of micromagnetic systems, ferromagnetic resonance (FMR), and spin-waves, including the mathematical description of spin-wave dispersion relations. This is followed by the description of experimental methods. Then we present the first experimental part concerning the nucleation process of magnetic vortices, i.e., the transition from the saturated state into the vortex spin configuration while decreasing the magnetic field. Magnetic imaging methods are used, namely Lorentz transmission electron microscopy and magnetic transmission X-ray microscopy. The results are correlated with electrical detection using the anisotropic magnetoresistance effect. The advantage of electrical measurements is their potential integrability into the microprocessor circuitry. In the results, we report that this process in nanometer- and micrometer-sized magnetic disks undergoes several phases with distinct spin configurations called the nucleation states. Moreover, we introduce the analysis of magnetic materials using a vector network analyzer (VNA), which is applied to the measurement of magnetic vortex resonance (evaluation of the gyrotropic frequency and the high-frequency modes as well), the ferromagnetic resonance of thin layers (extraction of basic magnetic material parameters), and propagating spin-wave spectroscopy (PSWS). Spin-wave spectroscopy is further developed to measure the dispersion relations of thin magnetic layers, which can serve as an essential characteristic used in the design of devices. Finally, we show a concept of an antenna device, separating the magnetic excitation from the sample itself, providing no need for electron lithography processes of the antenna fabrication onto the sample. This device has the form of a glass cantilever, on which the excitation antenna is fabricated, a connector, and a coupler. It is then placed on a tilt equipped x-y-z stage, and therefore it provides positionability to any place on the measured sample. The use of glass as the cantilever material enables navigation using a microscope and enables the use of optical detection methods, e.g., Brillouin light scattering (BLS) or Kerr effect.
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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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Disperzní relace magnonických krystalů s netriviální prostorovou distribucí magnetické anizotropie
Wojewoda, Ondřej ; Hamrle,, Jaroslav (oponent) ; Flajšman, Lukáš (vedoucí práce)
Magnonika je poměrně novým vědním oborem zabývajícím se spinovými vlnami, což jsou kolektivní excitace magnetizace. Základními stavebními prvky magnonických obvodů, které umožňují kontrolu nad disperzí spinových vln jsou magnonické krystaly. Jejich periodická struktura zapříčiní vznik komplexní pásové struktury s pásem zakázaných frekvencí. Periodické struktury lze klasicky dosáhnout modulací tloušťky materiálu nebo skokovou změnou saturační magnetizace. Předložená práce se zabývá teoretickým popisem disperzních relací magnonických krystalů, kde je periodicity systému dosahováno modulací směru uniaxiální magnetické anizotropie a kontinuální změnou saturační magnetizace. Pro lepší vhled do chování spinových vln v prostředí se změnou magnetických vlastností je uvedena teorie popisující lom a odraz spinových vln na rozhraní, která byla dále ověřena numerickými simulacemi.
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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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Magneto-optical study of the dynamic properties of magnetic nanostructures and nanostructured metamaterials
Flajšman, Lukáš ; Chumak, Andrii (oponent) ; Revelosona, Dafiné (oponent) ; Spousta, Jiří (vedoucí práce)
The magnonics is the novel research topic in magnetism concerned with the physics of spin waves. The magnonics has the potential to introduce novel devices for wave-based computing with low power consumption. During the fabrication process of the magnonic devices using common materials and fabrication techniques, we are left only with a minimum means of how to alter the inherent properties of the magnetic materials. This highly limits the usability or versatility of the structures. This work introduces a novel material to the magnonics. The unique and highly deterministic properties of the structures prepared by focused ion beam direct writing into the metastable iron layer are presented and partially exploited in a set of prototypical structures prepared in the system. The important parameters of the system are extracted from the measurement of the spin-wave dispersion by the means of the phase-resolved Brillouin light scattering method. The findings are supported by the micromagnetic simulations and by using the analytical models. Three sets of novel magnonic devices that exploit the unique properties of the system are presented and tested.
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Parametrické pumpování jako zdroj krátkovlnných spinových vln
Pavelka, Dominik ; Zadorozhnii, Oleksii (oponent) ; Holobrádek, Jakub (vedoucí práce)
Spinové vlny mají potenciál sehrát klíčovou roli v oblasti moderních informačních technologií, jelikož mohou přenášet informaci s minimálními energetickými ztrátami. Pro účely implementace součástek založených na spinových vlnách do logických obvodů je nezbytné tyto součástky miniauturizovat. K tomuto účelu je zapotřebí krátkovlnných spinových vln a efektivních metod, jak je vybudit. Tato bakalářská práce se věnuje metodě buzení spinových vln parametrickým pumpováním. Pojednává o teorii potřebné pro pochopení této problematiky, a především zachycuje průběh plánování a provedení experimentu. Pro experiment byl navržen a vyroben vzorek s nanoanténami vhodnými pro parametrické pumpování krátkovlnných spinových vln. Výsledky měření na tomto vzorku potvrzují přítomnost parametricky pumpovaných spinových vln a zobrazují jejich závislost na frekvenci a amplitudě budicího pole. Práce přispívá k rozšíření našeho porozumění parametrickému pumpování spinových vln a bude na ni navazovat další výzkum využívající výsledků dosažených v této práci.
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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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Magnetism in curved geometries
Turčan, Igor ; Makarov, Denys (oponent) ; Grundler, Dirk (oponent) ; Urbánek, Michal (vedoucí práce)
In the field of magnonics, which is a novel research topic utilizing the physics of spin waves, there is an increasing interest in developing functional spin-wave devices with unique properties. These devices allow us to control the spin-wave flow and are needed for future spin-wave-based information processing. However, their technical realization is highly challenging with conventional approaches. They rely on planar magnonic structures, where the magnetic properties are exclusively given by the intrinsic parameters of used materials. Thus, properties like uniaxial magnetic anisotropy cannot be directly controlled. The presented thesis exploits a novel approach of inducing the effective magnetic interaction by the curvature of the system. The corrugation-induced uniaxial magnetic anisotropy is studied in structures with modulated surfaces prepared by focused electron beam-induced deposition and electron beam lithography. The potential of the local control over the magnetization direction using the 3D nanofabrication approach is universal and can be used with any commonly used magnetic material. Furthermore, the spin-wave propagation in the Damon-Eshbach geometry without an external magnetic field is demonstrated in corrugated magnetic waveguides by means of Brillouin light scattering microscopy. The broadening of the ferromagnetic resonance peak and extraction of the damping parameter is presented for the planar and corrugated structures. Finally, the comparison of the spin-wave propagation length measurement in corrugated waveguides with the total damping measurements, and with analytical calculations is shown. The decrease of the propagation length for the waveguides with larger modulation amplitude is associated to the increase of the damping parameter.
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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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