Estudo de efeitos de Faraday e Kerr ópticos em estruturas multicamadas com efeito de transmissão óptica extraordinária

Neste trabalho foi investigada e otimizada uma nova heteroestrutura planar de três camadas com efeitos magneto-ópticos de Faraday e de Kerr aprimorados e transmissão óptica extraordinária na região de comprimento de onda de 925 a 1200 nm. Esta estrutura consiste de uma placa metálica não magnética de ouro perfurada periodicamente e colocada sobre duas finas camadas dielétricas, sendo uma composta por um material não magnético e outra composta por um material magnético (Bi-substituted Yttrium Iron Garnet) uniformemente magnetizado perpendicularmente ao seu plano. Analisando e otimizando esta estrutura, obteve-se rotação de Faraday e rotação de Kerr três vezes e nove vezes maior, respectivamente, que os de dispositivos análogos publicados na literatura. Além disso, esta estrutura foi otimizada para obter um aumento de 40% da transmissão óptica extraordinária, preservando o ângulo de rotação de Faraday. A heteroestrutura investigada pode ser utilizada em dispositivos ópticos não recíprocos.

Nanopartículas magnéticas de 'FE''CO'@'AU': preparação, caracterização e funcionalização com complexo de 'RU'(II) luminescente

Pós-graduação em Química - IQ

Faraday rotation in graphene

We study magneto-optical properties of monolayer graphene by means of quantum field theory methods in the framework of the Dirac model. We reveal a good agreement between the Dirac model and a recent experiment on giant Faraday rotation in cyclotron resonance [23]. We also predict other regimes when the effects are well pronounced. The general dependence of the Faraday rotation and absorption on various parameters of samples is revealed both for suspended and epitaxial graphene.

Influence of defects and disorder on anomalous Hall effect and spin Seebeck effect on permalloy and Heusler compounds

In dieser Arbeit wurden dünne Schichten von Heusler-Verbindungen hergestellt und auf ihre Transporteigenschaften hin untersucht.rnDer Anomale Hall-Effekt (AHE) ist dabei von besonderem Interesse. Er ist ein seit langer Zeit bekannter, jedoch noch nicht vollständig verstandener Transport-Effekt. Die meisten Veröffentlichungen theoretischer Arbeiten konzentrieren sich auf den Einfluss eines bestimmten Beitrags zum AHE. Tatsächlich gemessene experimentelle Daten können jedoch oft nicht in Einklang mit idealisierten Annahmen gebracht werden. rnDie vorliegende Arbeit diskutiert die Ergebnisse, welche aus Messungen von Materialien mit niedrigem Restwiderstand erhalten wurden. rnrnAls prototypische Materialien wurden hier hyphenation Heusler-Verbindungen untersucht. Als Material mit einer komplexen Topologie der Fermi-Fläche zeichnet sich dort der Einfluss von Defekten und der Unordnung der Kristallstruktur deutlich ab.rnrnDurch Verwendung von Filmen mit unterschiedlichem Grad der Unordnung können verschiedene Streumechanismen unterschieden werden. Für Co$_{2}$FeSi$_{0.6}$Al$_{0.4}$ and Co$_{2}$FeGa$_{0.5}$Ge$_{0.5}$ zeigt sich ein positiver AHE bei einer Unordnung vom Typ B2 und bei einer induzierten temperaturabh"angigen Streuung, wo hingegen eine Typ DO$_{3}$-Unordnung zusammen mit anderen möglichen intrinsischen Beiträgen einen negativen Effekt hervorruft.rnrnDarüber hinaus wurden die magneto-optische Kerr-Effekte (MOKE) dieser Verbindungen untersucht. Hierfür wurden Beiträge erster Ordnung als Funktion der intrinsischen und extrinsischen Parameter qualitativ analysiert. Auf den Einfluss der kristallinen Ordnung auf Beiträge zweiter Ordnung des MOKE-Signals wird ebenfalls eingegangen.rnrnDes Weiteren wurden dünne Schichten der Heusler-Verbindung Co$_{2}$MnAl auf MgO- und Si-Subs-traten (beide (100)) mit Hochfrequenz-Mag-netron-Sputtern erzeugt. Die zusammensetzung sowie die magnetischen und Transport-Eigenschaften wurden hinsichtlich unterschiedlicher Abscheidebedingungen systematisch untersucht.rnrnInsbesondere zeigt der AHE-Widerstand ein außerordentliches temperaturunabhängiges Verhalten in einem Bereich moderater Magnetfeldstärken von 0 bis 0.6,T. Hierf"ur wurde der nicht-diagonale Transport bei Temperaturen bis zu 300,$^{circ}$C analysiert. Die Daten zeigen die Eignung des Materials für Hall-Sensoren auch oberhalb der Raumtemperatur.rnrnJüngst wurde der Spin Seebeck-Effekt (SSE) entdeckt. Der Effekt aus dem Bereich der Spin-Kaloritronik erzeugt eine Spin-Spannung'' aufgrund eines Temperaturgradienten in magnetischen Materialien. Hier werden vorläufige Messungen des SSE in Ni$_{80}$Fe$_{20}$ und in Heusler-Verbindungen präsentiert.rn

Studio mediante magnetometro moke di film sottili di manganite per applicazioni in spintronica.

In questo lavoro di tesi è stata studiata l'anisotropia magnetica di film sottili epitassiali di La0.7Sr0.3MnO3 (LSMO), cresciuti con la tecnica Channel Spark Ablation su substrati monocristallini di SrTiO3 (001). L'interesse nei confronti di questi materiali nasce dal fatto che, grazie alla loro proprietà di half-metallicity, sono usati come iniettori di spin in dispositivi per applicazioni in spintronica, l'elettronica che considera elemento attivo per l'informazione non solo la carica elettrica ma anche lo spin dei portatori. Un tipico esempio di dispositivo spintronico è la valvola di spin (un dispositivo costituito da due film ferromagnetici metallici separati da uno strato conduttore o isolante) il cui stato resistivo dipende dall'orientazione relativa dei vettori magnetizzazione (parallela o antiparallela) degli strati ferromagnetici. E’ quindi di fondamentale importanza conoscere i meccanismi di magnetizzazione dei film che fungono da iniettori di spin. Questa indagine è stata effettuata misurando cicli di isteresi magnetica grazie ad un magnetometro MOKE (magneto-optical Kerr effect). Le misure di campo coercitivo e della magnetizzazione di rimanenza al variare dell'orientazione del campo rispetto al campione, permettono di identificare l'anisotropia, cioè gli assi di facile e difficile magnetizzazione. I risultati delle misure indicano una diversa anisotropia in funzione dello spessore del film: anisotropia biassiale (cioè con due assi facili di magnetizzazione) per film spessi 40 nm e uniassiale (un asse facile) per film spessi 20 nm. L'anisotropia biassiale viene associata allo strain che il substrato cristallino induce nel piano del film, mentre l'origine dell'uniassialità trova la giustificazione più probabile nella morfologia del substrato, in particolare nella presenza di terrazzamenti che potrebbero indurre una step-induced anisotropy. Il contributo di questi fattori di anisotropia alla magnetizzazione è stato studiato anche in temperatura.

Deflexiones transversales de radiación luminosa en estructuras prismáticas de cristal líquido

A novel structure , based on a wedge shaped configuration, is presented . This structure , previously used in one of his forms,for refraction index measurements is analysed in this paper. The results obtained give the possibility of his use in electro snd magneto-optical modulation and deflection.

Quantum dynamics with stochastic gauge simulations

The general idea of a stochastic gauge representation is introduced and compared with more traditional phase-space expansions, like the Wigner expansion. Stochastic gauges can be used to obtain an infinite class of positive-definite stochastic time-evolution equations, equivalent to master equations, for many systems including quantum time evolution. The method is illustrated with a variety of simple examples ranging from astrophysical molecular hydrogen production, through to the topical problem of Bose-Einstein condensation in an optical trap and the resulting quantum dynamics.

Epitaxial growth and magnetic properties of half-metallic Fe3O4 on GaAs(100)

The growth and magnetic properties of epitaxial magnetite Fe3O4 on GaAs(100) have been studied by reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, magneto-optical Kerr effect, and x-ray magnetic circular dichroism. The epitaxial Fe3O4 films were synthesized by in situ post growth annealing of ultrathin epitaxial Fe films at 500K in an oxygen partial pressure of 5×10−5mbar. The XMCD measurements show characteristic contributions from different sites of the ferrimagnetic magnetite unit cell, namely, Fetd3+, Feoh2+, and Feoh3+. The epitaxial relationship was found to be Fe3O4(100)⟨011⟩∕∕GaAs(100)⟨010⟩ with the unit cell of Fe3O4 rotated by 45° to match that of GaAs(100) substrate. The films show a uniaxial magnetic anisotropy in a thickness range of about 2.0–6.0nm with the easy axes along the [011] direction of the GaAs(100) substrate.

Photochemical dynamics of laser-irradiated semiconductor nanostructures

Thesis (Ph.D.)--University of Washington, 2016-08

Optics-Based Quantum Information and Sensing Platforms Utilizing the Nitrogen-Vacancy Center in Diamond

Thesis (Ph.D.)--University of Washington, 2016-08

OC-OT-LIBS: A novel approach to the chemical characterization of single particles

Spectral identification of individual micro- and nano-sized particles by the sequential intervention of optical catapulting, optical trapping and laser-induced breakdown spectroscopy is presented [1]. The three techniques are used for different purposes. Optical catapulting (OC) serves to put the particulate material under inspection in aerosol form [2-4]. Optical trapping (OT) permits the isolation and manipulation of individual particles from the aerosol, which are subsequently analyzed by laser-induced breakdown spectroscopy (LIBS). Once catapulted, the dynamics of particle trapping depends on the laser beam characteristics (power and intensity gradient) and on the particle properties (size, mass and shape). Particles are stably trapped in air at atmospheric pressure and can be conveniently manipulated for a precise positioning for LIBS analysis. The spectra acquired from the individually trapped particles permit a straightforward identification of the inspected material. The current work focuses on the development of a procedure for simultaneously acquiring dual information about the particle under study via LIBS and time-resolved plasma images by taking advantage of the aforementioned features of the OC-OT-LIBS instrument to align the multiple lines in a simple yet highly accurate way. The plasma imaging does not only further reinforce the spectral data, but also allows a better comprehension of the chemical and physical processes involved during laser-particle interaction. Also, a thorough determination of the optimal excitation conditions generating the most information out of each laser event was run along the determination of parameters such as the width of the optical trap, its stability as a function of the laser power and the laser wavelength. The extreme sensibility of the presented OC-OT-LIBS technology allows a detection power of attograms for single/individual particle analysis.

Diffusion of localized optical excitations and trap emission in ruby

Using the critical percolation conductance method the energy-dependent diffusion coefficient associated with thermally assisted transfer of the R1 line excitation between single Cr3+ ions with strain-induced randomness has been calculated in the 4A2 to E(2E) transition energies. For localized states sufficiently far away from the mobility edge the energy transfer is dominated by dipolar interactions, while very close to the mobility edge it is determined by short-range exchange interactions. Using the above energy-dependent diffusion coefficient a macroscopic diffusion equation is solved for the rate of light emission by Cr3+ ion-pair traps to which single-ion excitations are transferred. The dipolar mechanism leads to good agreement with recent measurements of the pair emission rate by Koo et al. (Phys. Rev. Lett., vol.35, p.1669 (1975)) right up to the mobility edge.

Magneto-transport and optical properties of diluted magnetic semiconductor Ga1-xMnxSb

We have studied magneto-transport and optical properties of Ga1-xMnxSb crystals (x = 0.01, 0.02, 0.03 and 0.04) grown by horizontal Bridgman method. Negative magnetoresistance and anomalous Hall effect have been observed below 10K. Temperature dependence of magnetization measurement shows a magnetic ordering below 10K which could arise from Ga1-xMnxSb alloy formation. Also, saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic MnSb clusters. Reduction in band gap is observed with increasing Mn concentration in the crystals. Temperature dependence of band gap follows Bose-Einstein's model.

Dual-trap optical tweezers with real-time force clamp control

Single molecule force clamp experiments are widely used to investigate how enzymes, molecular motors, and other molecular mechanisms work. We developed a dual-trap optical tweezers instrument with real-time (200 kHz update rate) force clamp control that can exert 0–100 pN forces on trapped beads. A model for force clamp experiments in the dumbbell-geometry is presented. We observe good agreement between predicted and observed power spectra of bead position and force fluctuations. The model can be used to predict and optimize the dynamics of real-time force clamp optical tweezers instruments. The results from a proof-of-principle experiment in which lambda exonuclease converts a double-stranded DNA tether, held at constant tension, into its single-stranded form, show that the developed instrument is suitable for experiments in single molecule biology.