Magnetic materials when reduced to the nanoscale promote the emergence of new properties and the specific functionalization of these magnetic nanostructures are key tools in the development of improved devices for information technology (memory and data processing) and detection. In this thesis were electro-deposited magnetic nanotubes in anodic aluminum membranes. The properties of magnetic nanotube networks of Ni, Co, FeCo and FeNi with different geometric parameters were investigated. The porous aluminum oxide membranes were prepared using the hard anodizing process, in a self-ordering regime with pore distances Dint=300nm. This process offers substantial advantages over conventional anodizing processes in terms of processing time, allowing for faster oxide growth, with better arrangement and high aspect ratio of nanopores. The nanotubes were electrodeposited through the potentiostat mode, using porous membranes as the basis for their structure. Samples with external diameter of 140nm, 180nm and 220nm were obtained. In addition, the nanotubes have an additional degree of freedom given by the thickness of the tube walls. In this way, nanotubes with constant external diameter and different wall thicknesses of the tube were also synthesized. The structure and morphologies of the synthesized samples were characterized by scanning electron microscopy, x-ray dispersion spectroscopy and x-ray diffraction. The magnetic characterization was performed through the vibrating sample magnetometer. Through the nanotubes with different diameters it was possible to observe that the global anisotropy of the matrix is the result of the competition between the magnetostatic interactions, magnetocrystalline anisotropy and form anisotropy. With the increase of the diameter of NTs and the decrease of the distance between them it was observed that the magnetostatic interactions prevail. Nanotubes with different wall thicknesses were produced, maintaining constant the external diameter and the distance between the structures. Through the characterization of these structures it was observed that for nearby nanotubes, with distances smaller than their diameter, it is the wall thickness that determines the magnetic interaction between the nanotubes of the network. The magnetization inversion processes for NTs with different wall thicknesses were investigated through the analysis of the coercive field as a function of the applied field. It can be seen that the same structure can present two types of magnetization inversion, the transverse mode or vortex, and that this inversion can be determined by adjusting the NT wall thickness. The comparative study between the nanotubes with different compositions and geometric parameters showed that the magnetic properties are strongly correlated with the geometric parameters. / Materiais magnéticos quando reduzidos à escala nanométrica promovem o surgimento de novas propriedades e a funcionalização específica dessas nanoestruturas magnéticas são ferramentas chave no desenvolvimento de dispositivos aprimorados para tecnologia da informação (memória e processamento de dados) e detecção. Nesta tese foram sintetizados nanotubos magnéticos eletrodespositados em membranas de alumínio anódico. Foram investigadas as propriedades de redes de nanotubos magnéticos de Ni, Co, FeCo e FeNi, com diferentes parâmetros geométricos. As membranas de óxido de alumínio poroso foram preparadas utilizando o processo de anodização dura, em um regime de auto-ordenação com distâncias entre poros Dint=300nm. Este processo oferece vantagens substanciais em relação aos processos convencionais de anodização em termos do tempo de processamento, permitindo um crescimento mais rápido de óxido, com um melhor ordenamento e alta razão de aspecto dos nanoporos. Os nanotubos foram eletrodepositados através do modo potenciostato, utilizando as membranas porosas como base para sua estrutura. Foram obtidas amostras com diâmetro externo de 140nm, 180nm e 220nm. Além disso, os nanotubos apresentam um grau de liberdade adicional dado pela espessura das paredes do tubo. Dessa forma, também foram sintetizados nanotubos com diâmetro externo constante e com diferentes espessuras de parede do tubo. As estrutura e morfologias das amostras sintetizadas foram caracterizadas por microscopia eletrônica de varredura, espectroscopia de dispersão de raio-x e difratometria de raio-x. A caracterização magnética foi realizada através do magnetômetro de amostra vibrante. Através dos nanotubos com diferentes diâmetros foi possível observar que a anisotropia global da matriz é o resultado da competição entre as interações magnetostáticas, anisotropia magnetocristalina e anisotropia de forma. Com o aumento do diâmetro dos NTs e a diminuição da distância entre eles foi observado que as interações magnetostáticas prevalecem. Nanotubos com diferentes espessuras de parede foram produzidos, mantendo constante o diâmetro externo e a distância estre as estruturas. Através da caracterização dessas estruturas foi observado que para nanotubos próximos, com distâncias menores que seu diâmetro, é a espessura da parede que determina a interação magnética entre os nanotubos da rede. Os processos de inversão de magnetização para NTs com diferentes espessuras de parede foi investigado através da análise do campo coercivo em função do campo aplicado. Mostrando que a mesma estrutura pode apresentar dois tipos de inversão de magnetização, o modo transversal ou vórtice, e que esta inversão pode ser determinada através do ajusta da espessura de parede do NT. O estudo comparativo entre os nanotubos com diferentes composições e parâmetros geométricos mostrou que as propriedades magnéticas são fortemente correlacionadas com os parâmetros geométricos.

Das Thema dieser Arbeit ist die Synthese von Ferromagnet-Halbleiter-Nanodraht-Strukturen in einer Kern-Hülle-Geometrie. Diese wird mittels Molekularstrahlepitaxie unter der Verwendung von GaAs und Fe3Si ausgeführt. Im Zentrum der Arbeit steht die Frage, ob sich mit derartigen Strukturen Magnetisierungen senkrecht zum Substrat realisieren lassen. Eine solche Konfiguration der Magnetisierung innerhalb bestimmter Strukturen ist wünschenswert, denn sie bildet die Grundlage einiger zukunftsweisender spintronischer Bauteilkonzepte. Aufgrund der Formanisotropie dünner Schichten ist diese Konfiguration der Magnetisierung in planaren Strukturen nur mit erheblichem Aufwand zu bewerkstelligen. Bildet sich hingegen in den Nanodraht-Hüllen eine Stabmagnetisierung aus, so führt dies direkt zur gewünschten senkrechten Magnetisierung. Im ersten Teil dieser Arbeit wird der Epitaxie-Prozess vorgestellt. Abhängig von den Wachstumsparametern können Hüllen mit glatten Seitenflachen, einer hohen Kristallordnung, ebenen Grenzflachen zum GaAs-Kern und epitaktischer Ausrichtung realisiert werden. Der zweite Teil behandelt die magnetischen Eigenschaften der Nanodrahte. Ensemble-Charakterisierungen sind hierbei in diesem Fall nicht geeignet. Einzeldraht-Messungen hingegen zeigen, dass sich in den Nanodraht-Hüllen wie erhofft eine Stabmagnetisierung ausbildet. Der dritte und letzte Teil dieser Dissertation umfasst die Einführung mehrerer zukunftsweisender Bauteilkonzepte, basierend auf den speziellen magnetischen Eigenschaften der hier vorgestellten Nanodrahte. Dazu gehören dreidimensionale Speicherarchitekturen mit bislang unerreichten Speicherkapazitäten und zirkular polarisiertes Licht emittierende Leuchtdioden für einen enorm schnellen Spininformations-Transfer zur Intrachip-Kommunikation. / The subject of the present work is the synthesis of ferromagnet-semiconductor coreshell nanowires. To realize such structures molecular beam epitaxy has been employed. For the investigation the well-suited materials systems GaAs and Fe3Si are used. Within the framework of this thesis the open question whether a magnetization in the nanowires that is perpendicular to the nanowire’s substrate can be realized is of special interest. Such a configuration of the magnetization is desirable, because some spintronic device concepts rely on magnetizations perpendicular to the substrate. In general, with the exception of very limited and highly specific materials, the shape anisotropy of thin magnetic layers causes the magnetic moments to orient along an in-plane direction and therefore, perpendicular configurations of the magnetization do not occur at equilibrium conditions. In contrast, magnetic nanowires with moments pointing along the wire axis directly provide the desired out-of plane magnetization. In the first part, the epitaxial procedure to realize the core-shell nanowires is described. Nanowires with smooth side walls, smooth interface to the GaAs core, a fairly high structural ordering and an epitaxial orientation relationship are produced. In the second part, the magnetic properties of the core-shell nanowires are analyzed. It is shown that characterizations of an ensemble of wires cannot resolve magnetic properties of the shells. Investigations on single nanowires however revealed that the magnetization in the shells is indeed as desired oriented along the wires. Several innovative device concepts based on the specific magnetic properties of these core-shell nanowires are finally introduced in the third part of this work. Within these concepts three-dimensional magnetic recording devices with unsurpassed data storage capacities and circular polarized light emitting diodes for tremendously fast spin information transfer for intrachip communication can be realized.