Sistema de baixa dimensionalidade tÃm atraÃdo uma grande atenÃÃo ultimamente devido a sistemas como grafeno e nanotubos de carbono. Tais sistemas tÃm grandes possibilidades de aplicaÃÃes tecnolÃgicas, em particular na criaÃÃo de dispositivos eletrÃnicos, devido Ãs suas propriedades eletrÃnicas especÃficas. Nesse sentido, o estudos de outros sistemas em baixa dimensÃo se torna urgente. Mais especificamente, o estudo de propriedades magnÃticas de materiais de materiais em baixa dimensionalidade tambÃm trÃs grandes novidades no comportamento de sistemas ferromagnÃticos. O comportamento de ondas de spin em tais sistemas pode ser para o estudo da spintrÃnica e o desenvolvimento de novos aparelhos e memÃrias magnÃticas. Dessa forma temos como objetivo nesse trabalho estudar o comportamento de ondas de spin em sistemas bidimensionais ferromagnÃticos. Por sistemas bidimensionais consideramos aqui redes bidimensionais decoradas. As decoraÃÃes sÃo introduzidas para gerar redes com mais de um Ãtomo na base da cÃlula unitÃria da rede para estudarmos a riqueza do espectro das ondas de spin devido a essas modificaÃÃes. A princÃpio tratamos com uma superposiÃÃo de redes quadradas onde o deslocamento dessas redes depende dos parÃmetros de controle α e β. TambÃm usamos a superposiÃÃo de um rede quadrada sobre um hexagonal / Low-dimensional systems have attracted much attention lately due to systems such as graphene and carbon nanotubes. Such systems have great potential for technological applications. In particular the creation of electronic devices due to their specific electronic properties. In this sense , the study of other systems in low dimension becomes urgent. More specifically , the study of magnetic properties of materials at low dimensionality also brings great new features in the behavior of ferromagnetic systems . The behavior of spin waves in such systems may be important to the study of spintronic and the development of new devices and magnetic memories . Thus in this work we aim to study the behavior of ferromagnetic spin waves in two-dimensional systems . For two-dimensional systems we consider here two-dimensional networks decorated . The decorations are introduced to generate networks with more than one basic atom in the unit cell of the system to study the richness of the spectrum of spin waves due to these changes . At first deal with a superimposition of square networks where the displacement of these networks depends on the control parameters alpha and beta . We also use the superposition of a square on a hexagonal network.

Spinové vlny mají potenciál být použity jako nová platforma pro přenos a zpracování dat, protože mohou dosáhnout vlnových délek v rozsahu nanometrů a frekvencí v rozsahu terahertzů. K tomu, aby bylo možné navrhnout zařízení a logické obvody založené na spinových vlnách, je zapotřebí získat informace o prostorovém rozložení intenzity spinové vlny a pokud je to možné, také o jejich fázi. To lze měřit pomocí fázově rozlišeného fokuso-vaného Brillouinova rozptylu světla (µ -BLS). Předložená práce se zabývá rozšířením stávající optické sestavy o možnost měření fáze, kde doposud bylo možné měřit pouze intenzitu. Toto rozšíření sestavy je důkladně popsáno a charakterizováno. Schopnosti optické sestavy jsou demonstrovány ve studii šíření spinových vln skrz Néelovu doménovou stěnu. Získané 2D mapy intenzity spinových vln ukazují, že propagace přes doménovou stěnu je ovlivněna topologicky vynucenou kruhovou Blochovou čarou ve středu doménové stěny a že režim propagace závisí na frekvenci spinových vln. V prvním režimu propagace se vytvoří dva svazky spinových vlny šířící se kolem kruhové Blochovy čáry, zatímco ve druhém režimu se spinové vlny šíří pouze středem. Fázově rozlišené µ-BLS měření odhaluje fázový po- sun spinových vln pro oba režimy. Mikromagnetické modelování spinových vln ukazuje rozrušení jejich fázových vlnoploch, které je třeba brát v úvahu při interpretaci měření a navrhování potenciálních zařízení. Mikromagnetické simulace ukazují, že vnější magnetické pole může být použito k pohybu kruhové Blochovy čáry ve stěně domény, a tedy k manipulaci spinových vln.

As CMOS technology scaling is fast approaching its fundamental limits, several new nano-electronic devices have been proposed as possible alternatives to MOSFETs. Research on emerging devices mainly focusses on improving the intrinsic characteristics of these single devices keeping the overall integration approach fairly conventional. However, due to high logic complexity and wiring requirements, the overall system-level power, performance and area do not scale proportional to that of individual devices. Thereby, we propose a fundamental shift in mindset, to make the devices themselves more functional than simple switches. Our goal in this thesis is to develop a new nanoscale fabric paradigm that enables realization of arbitrary logic functions (with high fan-in/fan-out) more efficiently. We leverage on non-equilibrium spin wave physical phenomenon and wave interference to realize these elementary functions called Spin Wave Functions (SPWFs). In the proposed fabric, computation is based on the principle of wave superposition. Information is encoded both in the phase and amplitude of spin waves; thereby providing an opportunity for compressed data representation. Moreover, spin wave propagation does not involve any physical movement of charge particles. This provides a fundamental advantage over conventional charge based electronics and opens new horizons for novel nano-scale architectures. We show several variants of the SPWFs based on topology, signal weights, control inputs and wave frequencies. SPWF based designs of arithmetic circuits like adders and parallel counters are presented. Our efforts towards developing new architectures using SPWFs places strong emphasis on integrated fabric-circuit exploration methodology. With different topologies and circuit styles we have explored how capabilities at individual fabric components level can affect design and vice versa. Our estimates on benefits vs. 45nm CMOS implementation show that, for a 1-bit adder, up to 40x reduction in area and 228x reduction in power is possible. For the 2-bit adder, results show that up to 33x area reduction and 222x reduction in power may be possible. Building large scale SPWF-based systems, requires mechanisms for synchronization and data streaming. In this thesis, we present data streaming approaches based on Asynchronous SPWFs (A-SPWFs). As an example, a 32-bit Carry Completion Sensing Adder (CCSA) is shown based on the A-SPWF approach with preliminary power, performance and area evaluations.

We investigated the antiferromagnetic phase transition in the frustrated and multiferroic hexagonal manganites h-YMnO3 (YMO) and h-(Y0.98Eu0.02)MnO3 (YEMO). Elastic neutron scattering was used to study, in detail, the phase transition in YMO and YEMO under zero pressure and in YMO under a hydrostatic pressure of 1.5 GPa. Under conditions of zero pressure, we found critical temperatures of TN = 71.3(1) K and 72.11(5) K and the critical exponent 0.22(2) and b = 0.206(3), for YMO and YEMO, respectively. This is in agreement with earlier work by Roessli et al. Under an applied hydrostatic pressure of 1.5 GPa, the ordering temperature increased to TN = 75.2(5) K, in agreement with earlier reports, while b was unchanged. Inelastic neutron scattering was used to determine the size of the anisotropy spin wave gap close to the phase transition. From spin wave theory, the gap is expected to close with a critical exponent, b0, identical to the order parameter b. Our results indicate that the gap in YEMO indeed closes at TN = 72.4(3) K with b0 = 0.24(2), while the in-pressure gap in YMO closes at 75.2(5) K with an exponent of b0 = 0.19(3). In addition, the low temperature anisotropy gap was found to have a slightly higher absolute value under pressure. The consistent values obtained for b in the two systems support the likelihood of a new universality class for triangular, frustrated antiferromagnets.

Dans cette thèse, nous proposons d’explorer la relation entre transport électronique et dynamique d’aimantation afin de mieux comprendre certaines propriétés des films minces de métaux ferromagnétiques. Afin d’extraire l’influencede la diffusion des électrons par les surfaces sur les résistivités dépendantes du spin, des séries d’épaisseur de films de permalloy (Ni80Fe20) ont été déposées et étudiées. En plus de mesures électriques et magnétiques conventionnelles,nous avons réalisé une étude détaillée de la propagation des ondes de spin dans ces films. La technique du décalage Doppler d’ondes de spin induit par un courant électrique a été utilisée pour extraire le degré de polarisation en spin du courant électrique. Nous avons observé que ce degré de polarisation décroît lorsque l’épaisseur du film décroît, ce qui suggère que les surfaces contribuent aux résistivités dépendantes du spin et qu’elles ont tendance à dépolariser le courant électrique. / In this thesis, the interplay between electron transport and magnetization dynamics is explored in order to access to fundamental properties of ferromag- netic metal thin films. With the aim of extracting the influence of the electron surface scattering on the spin-dependent resistivities, thickness series of permal-loy (Ni80Fe20) films were grown and studied. In addition to standard electrical and magnetic measurements, a detailed study of the propagation of spin waves along these films was performed. Resorting to the current-induced spin-wave Doppler shift technique, the degree of spin-polarization of the electrical current was extracted. This degree of spin-polarization was found to decrease when the film thickness decreases, which suggests that the film surfaces contribute to the spin dependent resistivities and tend to depolarize the electrical current.

Magnetické materiály a z nich vyrobené nanostruktury jsou v průběhu posledních let studovány pro jejich aplikace v např. záznamových médiích a logických obvodech. Tato práce navazuje na náš předchozí výzkum tohoto oboru s hlavním zaměřením na statické a dynamické vlastnosti nanostrukturovaných magnetických materiálů, jako například NiFe, CoFeB a YIG. Práce začíná teoretickým úvodem s popisem mikromagnetických systémů, dynamiky magnetických vortexů, feromagnetické rezonance (FMR) a spinových vln včetně jejich disperzních vlastností. Následuje popis použitých experimentálních metod a první experimentální část zabývající se nukleačním procesem magnetického vortexu, jinými slovy procesem transformace ze saturovaného stavu do spinové konfigurace magnetického vortexu v průběhu snižování magnetického pole. Jsou použity mikroskopické metody zobrazující magnetickou strukturu materiálu, jmenovitě Lorentzova transmisní elektronová mikroskopie a rentgenová transmisní mikroskopie. Výsledky jsou poté korelovány s měřením elektrické odezvy pomocí jevu anizotropní magnetorezistence. Výhodou elektrických měření je, že plně elektrická detekce dovoluje použití tohoto systému v uzavřených systémech integrovaných obvodů. Výsledky oblasti nukleací magnetických vortexů ukazují, že při tomto procesu prochází magnetizace v nano- a mikrometrových magnetických discích několika fázemi s růsnými typy spinových konfigurací nazvaných nukleační stavy. Dále je představeno měření magnetických materiálů pomocí vektorového síťového analyzátoru (VNA), což je aplikováno na měření resonance magnetických vortexů (určení gyrotropické frekvence a měření vysokofrekvenčních módů), feromagnetické rezonance tenkých vrstev (získání základních magnetických materiálových parametrů) a spektroskopii spinových vln. Právě spektroskopie spinových vlna je rozvinuta za účelem měření disperzních relací tenkých magnetických vrstev, což je základní charakteristika, jejíž znalost je důležitá v návrhu aplikací. Nakonec je představeno anténní zařízení, díky kterému lze oddělit magnetické buzení od vzorku samotného bez nutnosti absolvovat proces elektronové litorafie, což je zapotřebí v klasickém přístupu antény na vzorku a kontaktování vysokofrekvenční sondou. Toto zařízení se skládá ze skleněného kantilívru, na kterém je vyrobena budící anténa, konektoru a spojovacího prvku v podobě plošného spoje. Celé zařízení je díky umístění na x-y-z stolek s náklonem pozicovatelné a lze tedy měřit v jakémkoliv místě vzorku. Umístění antény na sklo umožňuje navigaci pomocí mikroskopu a optické měření, např. metodou Brillouinova světelného rozptylu (BLS) nebo Kerrova jevu.

<p>The ferrimagnetic electrical insulator yttrium iron garnet (YIG) has been proved a promising magnonic platform that allows for a variety of application within microwave fre- quency range. This dissertation focuses on the development of novel spin wave resonators and filters for next-generation radio frequency technology.</p> <p>Chapter 1 begins with an introduction to modern radio frequency communication tech- nology and motivation of our research on novel radio frequency devices.</p> <p>Chapter 2 discusses about the properties of yttrium iron garnet (YIG) thin film platform and theory of magnetostatic waves (MSW) within the magnetic thin film system. Three different types of magnetostatic wave modes, known as magnetostatic forward volume wave (MSFVW), magnetostatic backward volume waves (MSBVW) and magnetostatic surface wave (MSSW), are illustrated in this section. They have very distinct dispersion relations and require different transduction technology, which leads to disparate designs for devices utilizing different modes. The damping mechanism and linewidth of the magnetostatic modes will also be discussed in this chapter.</p> <p>Chapter 3 will showcase a new YIG-on-Si platform created using novel YIG bonding technology and the first ever on-chip MSFVW hairpin resonator on the YIG-on-Si platform. In the first part, we would like to show finite element analysis of YIG-on-Si MSFVW hairpin resonator and prove the capability of the hairpin transducer incorporated with YIG thin film to yield lower self-inductance and stronger excitation field. These unique properties are beneficial for generating high coupling between magnon and microwave domains. In the following sections, the bonding technology essential for creation of YIG-on-Si platform and key fabrication technology of hairpin devices are explained in detailed. With well defined fabrication process established, we will demonstrate that the hairpin magnetostatic wave resonator obtained through the process is magnetically tunable with a high coupling efficiency over 50%. An out-of-plane Z-directional tunable magnetic field results in forward volume spin-wave resonance with frequency in the 5G band. This technology enables us to build on-chip devices of desirable high coupling and magnetic tuning on the new YIG-on-Insulator platform and provides possibility of magnetic tuning and band-pass filter at radio-frequency range.</p> <p>Chapter 4 demonstrates a planar monolithic yttrium iron garnet (YIG) Chebyshev bandstop filter on traditional gadolinium gallium garnet (GGG) substrate with tunable frequency, low insertion loss and high rejection. This filter is created in YIG micro-machining technol- ogy that allows direct placement of metal transducers on YIG for strong spin-wave coupling. With an out-of-plane 3900 Oe bias field, the bandstop filter exhibits 55 dB maximum stop- band rejection at a center frequency of 6 GHz, with 2 dB passband insertion loss and 37.8 dBm passband <strong>IIP3</strong>. By applying different bias fields, the stopband center frequency is tuned from 4 GHz to 8 GHz while maintaining more than 30 dB rejection. Incorporated with proper design of tunable compact electromagnet, this new filter design can provide attenuation of spurs appearing across the 5G and X-band spectrum.</p> <p>In chapter 5, we will explore the properties of YIG thin-film materials in depth. Both YIG-on-Si and YIG-on-GGG platform under different conditions will be examined. Results of X-ray diffraction (XRD), ferromagnetic resonance (FMR), scanning tunneling microscope (STM) on the YIG thin films will be presented. Those results will cast light onto the study of limiting factors of our YIG-on-Si and YIG-on-GGG devices.</p>

Spintronics is the study of electron spins and their utilization in electronic devices. Within this field, spin-based oscillators have shown promise for mi- crowave signal generation as they can operate at high frequencies, are small in scale and are compatible with modern fabrication techniques. Among these oscillators are the spin Hall nano-oscillators (SHNOs). They are nanoscale thin-film structures driven by pure spin-current injection from a primary con- ductor into a ferromagnetic material. This process can be used to generate microwave signals through oscillations in the material’s magnetization. By constraining the current flow in the device to individual constrictions, an ar- ray arrangement of multiple oscillators can be realized. These oscillators can then be coupled together via their internal interactions to achieve mutual syn- chronization and improve their characteristics.In this work, a versatile micromagnetic modelling procedure for simulating constriction-based SHNOs and their synchronization dynamics in different ar- ray arrangements is presented. A case study of various 2x2 array geometries is conducted along with an exploration of higher-order networks of 4x4, 6x6 and 8x8 oscillators. A perturbative optimization algorithm is developed to improve excitation conditions and drive geometries into a synchronized regime. Lastly, a comparison to nonlinear auto-oscillator theory is presented to illustrate the dependence of generated signals on constriction sizes and the spacing between oscillators. Mutual synchronization between multiple oscillators is achieved and favourable geometry and excitation conditions are defined. The conducted simulations show good agreement with experimental results and illustrate the potential for future studies of SHNO characteristics through micromagnetic modelling. / Spinntronik är ett forskningsområde, som handlar om hur elektronens s.k. spinn kan användas i elektroniska komponenter. Inom detta område har spinnbaserade oscillatorer visat sig ha lovande egenskaper för generering av mikrovågssignaler, eftersom de har höga arbetsfrekvenser, liten storlek och är kompatibla med moderna tillverkningstekniker. En typ av dessa oscillatorer kallas spinn-Hall nano-oscillatorer (SHNO). De är nanometerstora tunnfilms- strukturer, vilka drivs av en ren spinnström, som injiceras från en (metallisk) ledare till en ett ferromagnetiskt material. Denna mekanism kan användas för att skapa mikrovågssignaler genom oscillationer i materialets magnetisering. Genom att begränsa strömflödet i komponenten till enskilda gap kan man skapa en matris med ett stort antal oscillatorer. Dessa oscillatorer kan sedan kopplas till varandra genom interna utbytesmekanismer och på så sätt uppnår man en ömsesidig koppling och förbättrade egenskaper.I detta arbete presenteras ett mångsidigt mikromagnetiskt modelleringsflö- de, för att simulera SHNO:er, baserade på nano-gap, och deras synkronisering i olika matriskonfigurationer. En fallstudie som inkluderar olika 2x2 matris- geometrier har genomförts tillsammans med explorativ utforskning av högre ordnings nätverk, såsom 4x4, 6x6 och 8x8 oscillatorer. En störnings-baserad optimerings-algoritm har utvecklats för att förbättra exciterings-parametrarna och för att tvinga geometrierna in i en synkroniserad regim. Som en avslutning presenteras en jämförelse med icke-linjär auto-oscillatorteori för att visa den genererade signalens beroende på gapens storlek och avståndet mellan dem. Ömsesidig synkronisering mellan flera oscillatorer kunde uppnås och en för- delaktig geometri samt lämpliga värden på exciterings-parametrarna kunde definieras. Simuleringarna i studien hade bra överensstämmelse med experi- mentella resultat och visar på potentialen för vidare studier av SHNO egen- skaper med hjälp av mikromagnetisk modellering.

<p>This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. Our calculations are done within the framework of the self-consistent spin-wave theory (SSWT), which is modified in order to include the dipolar interaction. Both quantum and classical versions of the Heisenberg model are considered.</p><p>The second part of the thesis investigates the chemical bonding in solids from the first principles calculations. A new chemical bonding indicator called balanced crystal orbital overlap population (BCOOP) is developed. BCOOP is less basis set dependent than the earlier indicators and it can be used with full-potential density-functional theory (DFT) codes. We apply BCOOP formalism to the chemical bonding in the high-T_c superconductor MgB2 and the theoretically predicted MAX phase Nb3SiC2. We also study how the chemical bonding results in a repulsive hydrogen–hydrogen interaction in metal hydrides. The role of this interaction in the structural phase transition in Ti3SnHx is investigated.</p>

This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. Our calculations are done within the framework of the self-consistent spin-wave theory (SSWT), which is modified in order to include the dipolar interaction. Both quantum and classical versions of the Heisenberg model are considered. The second part of the thesis investigates the chemical bonding in solids from the first principles calculations. A new chemical bonding indicator called balanced crystal orbital overlap population (BCOOP) is developed. BCOOP is less basis set dependent than the earlier indicators and it can be used with full-potential density-functional theory (DFT) codes. We apply BCOOP formalism to the chemical bonding in the high-T_c superconductor MgB2 and the theoretically predicted MAX phase Nb3SiC2. We also study how the chemical bonding results in a repulsive hydrogen–hydrogen interaction in metal hydrides. The role of this interaction in the structural phase transition in Ti3SnHx is investigated.