Aquest treball presenta l’estudi teòric de l’anisotropia magnètica en complexos de metalls de transició, combinant esquemes de càlcul multiconfiguracionals relativistes amb derivacions analítiques basades en la teoria del camp del lligand, el que permet racionalitzar a través de conceptes senzills els resultats quantitatius obtinguts i interpretar les propietats estudiades. Es desenvolupa primer una metodologia per extreure els paràmetres d’anisotropia en complexos mononuclears de metalls de transició. El mètode es basa en assignar els resultats d’un càlcul ab initio d’alt nivell a un Hamiltonià model mitjançant la teoria d’Hamiltonians efectius. Aquesta metodologia s’aplica a complexos de Ni(II), Co(II) i Mn(III) i es comprova que és aplicable de forma general a complexos mononuclears. S’estén després la metodologia a complexos binuclears, pels quals l’Hamiltonià model usualment utilitzat té una base menys rigorosa. L’Hamiltonià efectiu obtingut per un complex binuclear de Ni(II) introdueix una nova parametrització amb termes addicionals de les interaccions anisotròpiques en sistemes polinuclears. Es tracta d’un procediment universal que proporciona valors precisos i a més és capaç de contrastar la consistència interna dels Hamiltonians models existents. Per racionalitzar les correlacions magnetoestructurals dels paràmetres d’anisotropia en complexos de Ni(II) i Mn(III), es descriuen els mecanismes electrònics bàsics en base a consideracions de la teoria del camp del lligand. Aquest procediment proporciona regles senzilles per augmentar l’anisotropia, que poden ser aplicades en el disseny de nous materials. Finalment, s’estudien les interaccions anisotròpiques simètriques i antisimètriques en compostos binuclears de Cu(II), interaccions de gran importància per explicar les propietats d’alguns materials d’interès tecnològic. Les interaccions antisimètriques s’extreuen a partir de càlculs ab initio d’estructura electrònica per primer cop en aquest treball. Es concentra l’atenció d’aquesta part en dos sistemes: el conegut complex binuclear de Cu(II) amb quatre ponts acetat, i l’òxid de coure en el que recentment s’ha evidenciat una fase ferroelèctrica.

Les films minces déposés sur des substrats flexibles ont été intensivement étudiés ces dernières années en raison de leur nombreuses applications en électronique flexible. Depuis peu, l'électronique flexible est étendu aux matériaux magnétiques conduisant ainsi au domaine émergeant de la magnéto-électronique flexible actuellement à l'avant garde des sujets de recherche de la spintronique. Ce travail de thèse est dédié à l'étude des propriétés magnéto-mécaniques de films minces magnétiques (Ni, NiFe, Co2FeAl, CoFeB, FeCuNbSi) sur des substrats flexibles. Les analyses structurales ont montré que les films de Ni et de CFA sont polycristallins non-texturés ; le CFB est amorphe. Par conséquent, les propriétés élastiques et magnéto-élastiques de ces films sont considérées comme étant isotropes. Une technique basée sur une utilisation conjointe d'essai mécanique, la résonance ferromagnétique (FMR) et la corrélation d'images numériques (CIN) a été développée pour étudier les propriétés magnéto-mécaniques de films minces sur substrats flexibles. A l'aide de cette méthode, il est possible de suivre l'évolution de l'anisotropie résiduelle omniprésente dans les films magnétiques sur substrats flexibles. Cette anisotropie est liée aux propriétés mécaniques contrastées lorsqu'on dépose un film mince rigide (grand module d'Young) sur un substrat flexible (petit module d'Young). L'effet du recuit sur les propriétés élastiques et magnéto-élastiques a été soigneusement étudié dans le film CFB validant ainsi l'intérêt porté à ses alliages pour des applications en spintronique. Enfin, la résonance ferromagnétique est employé en balayage en fréquence pour suivre la variation de la direction de l'aimantation en fonction des déformations induites par l'application de tension électrique sur l'actionneur piézoélectrique. Un retournement de 90° de la direction de l'aimantation dans le film Co2FeAl sur substrat flexible de Kapton® est observé. / Thin films deposited on flexible substrates have been widely studied in the last decades due to the numerous applications in flexible electronics. Recently, flexible electronics have been extended to magnetic materials leading to the so-called emerging feld of flexible magnetoelectronics which is actually at the cutting-edge of spintronics research topics.This thesis is devoted to the study magnetomechanical properties of magnetic thin films (Ni, NiFe, Co2FeAl, CoFeB, FeCuNbSi) on flexible substrates. Structural analysis have 130 Abstracts hown that the Ni and CFA films are found to be polycrystalline with no strong preferred orientations ; the CFB film is amorphous. Consequently, the elastic and magnetoelastic properties are isotropic. For the study of the magnetomechanical properties, a set-up based on a jointly use of deformation test (bending or piezoactuation), ferromagnetic resonance (FMR) and digital image correlation (DIC) have been developped. Thanks to this method, it is possible to follow the evolution of the inescapable residual anisotropy encountered in magnetic thin films on flexible substrates under deformation and to determine the effective coefficient of magnetostriction of the films (sometimes unknown).This residual anisotropy is ascribed to contrasted mechanical strength when a sti thin film is deposited on a compliant substrate. The effect of the annealing temperature on the elastic and magnetoelastic have been studied carefully in CFB validating then theinterest on such alloys for spintronics applications. Finally, we have employed FMR inits sweep frequency mode to study the effective evolution of magnetization direction as function of the voltage-induced strains. A 90-degree magnetization rotation in Co2FeAl thin film on Kapton® polyimide substrate is observed.

Orientadores: Marcelo Knobel, Daniela Zanchet / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T12:53:07Z (GMT). No. of bitstreams: 1 Silva_ElvisLirada_M.pdf: 8983880 bytes, checksum: 9cf84b0bedd17ff35f94bf813d128441 (MD5) Previous issue date: 2006 / Resumo: Os arranjos de nanofios magnéticos tem atraído um interesse considerável da comunidade científica, motivado principalmente pela sua utilização como sistemas-modelo e na possível aplicação em mídias magnéticas de alta densidade de informação. O comportamento magnético macroscópico desses sistemas é fortemente dependente das anisotropias magnéticas efetivas (determinadas principalmente pelas contribuições das anisotropias de forma, magnetocristalina e magnetoelástica). Neste trabalho realizamos um estudo completo das propriedades magnéticas de nanofios magnéticos de Ni e Co, variando o comprimento dos nanofios e a temperatura das amostras. Os nanofios são obtidos por eletrodeposição em nanoporos de membranas de alumina preparadas por um duplo processo de anodização em substratos de alumínio. A caracterização estrutural dos nanofios foi feita por microscopia eletrônica de varredura de alta resolução e microscopia de força magnética e revela que os arranjos de nanofios estão organizados em uma rede hexagonal onde possuem diametros de aproximadamente 35 nm e a distância entre os nanofios de aproximadamente 105 nm. O comprimento dos nanofios varia de aproximadamente 560 nm até 2250 nm. Observamos uma mudança do eixo fácil de magnetização da direção paralela ao eixo dos nanofios na temperatura ambiente para direção perpendicular ao eixo dos nanofios em baixas temperaturas. Analisamos a dependência da remanência reduzida e da coercividade em relação à temperatura e verificamos que as amostras apresentam uma temperatura de cruzamento entre as remanências reduzidas com campo aplicado paralela e perpendicularmente ao eixo dos nanofios, que varia de acordo com o comprimento dos nanofios. Interpretamos nossos resultados em termos de uma competição entre a anisotropia de forma, que tende orientar a magnetização na direção paralela ao eixo dos nanofios, e uma anisotropia dependente da temperatura, que tenta alinhar a magnetizaçao na direção perpendicular ao eixo dos nanofios. O mecanismo utilizado para tentar explicar de maneira qualitativa os resultados que observamos, ao diminuirmos a temperatura da amostra, origina-se da tensão provocada pela alumina sobre os nanofios, em decorrência dos diferentes coeficientes de expansão térmica desses materiais, que induz uma anisotropia magnetoelástica perpendicular ao eixo dos nanofios / Abstract: Arrays of magnetic nanowires have attracted considerable interest, mainly motivated by their use as model systems and by possible applications in high-density magnetic information storage. The macroscopic magnetic behavior of such systems is strongly dependent on the effective magnetic anisotropy (mainly determined by shape and crystalline contributions). In this work, we carry out a systematic study of the magnetic properties on highly-ordered magnetic arrays of Co and Ni nanowires as functions of length of the nanowires and temperature. Nanowires were obtained by electrodeposition into nanopores of alumina membranes prepared by a two-step anodization process from pure aluminium. Structural studies were performed by high resolution scanning electron microscopy and magnetic force microscopy. The images revealed uniform arrays of nanowires with diameter of 35 nm, and with hexagonal symmetry arrangement with lattice constant (or inter-nanowire distance) of 105 nm. The nanowires length varies between 560 nm and 2250 nm. We observed a change in the magnetic easy axis from parallel to the axis wires at room temperature to transverse to the wire axis at low temperatures. We analysed the temperature dependence of the reduced remanence and coercive field we verified that the samples present a crossover temperature of reduced remanence with magnetic field applied both perpendicular and parallel to the nanowires axis that varies with nanowires length. We interpreted our results in terms of a competition between the shape anisotropy of the wires, which tends to align the magnetization along the wires axis and the temperature dependent magnetic anisotropy, which tends to orient the magnetization transverse to the wires axis. The mechanism which can qualitatively explain the observed results as a function of temperature is an induced anisotropy of magnetoelastic origin transversal to the nanowires axis, caused by strains and stresses, due to the different thermal expansion coefficient of nanowires and the alumina matrix, respectively / Mestrado / Materiais Magneticos e Propriedades Magneticas / Mestre em Física

Submitted by Erika Demachki (erikademachki@gmail.com) on 2015-01-16T17:15:31Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Tese - Márcio Solino Pessoa - 2013.pdf: 3016321 bytes, checksum: 0475321bc8fda0cf44f37f4a946b3725 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2015-01-16T17:30:10Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Tese - Márcio Solino Pessoa - 2013.pdf: 3016321 bytes, checksum: 0475321bc8fda0cf44f37f4a946b3725 (MD5) / Made available in DSpace on 2015-01-16T17:30:10Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Tese - Márcio Solino Pessoa - 2013.pdf: 3016321 bytes, checksum: 0475321bc8fda0cf44f37f4a946b3725 (MD5) Previous issue date: 2013-06-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work reports the study of magnetic anisotropy of Fe/Mn bilayers, and Fe/Mn/Fe and Fe/Mn/Co trilayers, grown by molecular beam epitaxy onto monocrystalline MgO(001) substrates. Samples were produced with the Fe layer grown at a temperature of 175 ° C, with a thickness of 5 or 10 nm, the Co layer grown at 50 ° C, with a thickness of 2 or 5 nm, and the Mn layer grown at temperatures of 50 ° C, 150 ° C or 175 ° C, with thicknesses in the range from 0.80 to 2.20 nm. The angular variations of the in-plane absorption field, at Q-band (33.9 Ghz) microwave frequency, reveal the presence of a large four-fold magnetic anisotropy in all studied films. In samples with thicker Mn layers, two uniform resonance modes of bcc-Fe and bcc-Co layers are excited by the microwave field. The angular variations of the in-plane absorption field reveal for both layers the presence of fourth order cubic magnetic anisotropy. Films with the Mn layer thickness exceeding 1.16 nm exhibits, however, only a single absorption mode due to the overlapping of Fe-bcc and Co-bcc uniform resonance modes. Experiments at X-band (9.4 GHz) microwave frequency reveal the excitation of non-aligned and non-resonant modes, suggesting, for samples with the Mn layer grown at low temperature, a non-collinear coupling between the magnetic layers in the presence of low-intensity magnetic fields. Four-fold magnetic anisotropy constants in the range from 3.0 x 105 to 4.8 x 105 erg/cm3 for the Fe layer, and from 2.0 x 105 to 6.4 x 105 erg/cm3, for the Co layer, are given by the experiments. The magnetic parameters deduced from the in-plane measurements at Q-band microwave frequency are used to fit the in-plane and out-of-plane angular variations of resonance fields at X-band frequency. / Este trabalho relata o estudo da anisotropia magnética em bicamadas Fe/Mn, e tricamadas Fe/Mn/Fe e Fe/Mn/Co, crescidas por epitaxia de feixe molecular sobre substratos monocristalinos de MgO (001). As amostras foram produzidas com a camada de Fe crescida à temperatura de 175°C, com espessura de 5 ou 10 nm, a camada de Co crescida à temperatura de 50°C, com espessura de 2 ou 5 nm, e a camada de Mn crescida a temperaturas de 50°C, 150°C ou 175°C, com espessuras na faixa de 0.80 a 2.20 nm. As variações angulares do campo de ressonância no plano dos filmes, em banda-Q (33.9 GHz) de frequência de micro-ondas, revelam a presença de anisotropia magnética cúbica de quarta ordem em todas as amostras estudadas. Para as tricamadas Fe/Mn/Co com menores espessuras da camada de Mn, os modos uniformes de ressonância de Fe e de Co, são excitados pelo campo oscilante de micro-ondas. As variações angulares de campo de ressonância no plano dos filmes revelam a presença de anisotropia magnética de quarta ordem nas duas camadas. Filmes com camada de Mn com espessura superior a 1.16 nm apresentam, entretanto, apenas um modo uniforme de ressonância, atribuído à sobreposição dos modos uniformes de ressonância das camadas de Fe-bcc e de Co-bcc, como resultado de efeitos de interface que reduzem a diferença entre as magnetizações efetivas das duas camadas. Experimentos em banda-X (9.4 GHz) de frequência de micro-ondas revelam a presença de modos não alinhados e não ressonantes, sugerindo, para amostras com camada de Mn crescida em baixa temperatura, um acoplamento não colinear entre as camadas magnéticas na presença de campo magnético de baixa intensidade. Constantes de anisotropia cúbica de 3.0 x 105 a 4.8 x 105 erg/cm3 para a camada de Fe, e de 2.0 x 105 a 6.4 x 105 erg/cm3, para a camada de Co, são deduzidos dos experimentos. Os parâmetros magnéticos deduzidos das variações angulares do campo de ressonância no plano das amostras, em banda-Q de frequência de micro-ondas, são usados para simular em banda-X as variações angulares do campo de ressonância no plano e fora do plano dos filmes.

Orientador: Kleber Roberto Pirota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T03:13:48Z (GMT). No. of bitstreams: 1 Carvalho_PetersonGrandinide_M.pdf: 8255135 bytes, checksum: 51addf2df8b7383dc2ab652f85205ea2 (MD5) Previous issue date: 2013 / Resumo: Redes de nanofios (NF) magnéticos têm atraído muita atenção devido suas possíveis aplicações tecnológicas. Do ponto de vista tecnológico tais redes poderiam ser utilizadas em diversas aplicações tais como dispositivos spintrônicos, sistemas de armazenamento de memória magnética, elementos sensores de campo magnético e em diversas aplicações biológicas. Por outro lado, do ponto de vista da ciência de base é fundamental compreender o efeito da baixa dimensionalidade nas propriedades magnéticas dos materiais. Muitas das propriedades magnéticas dos NF decorrem simplesmente de sua geometria. Neles, há uma forte anisotropia magnética de forma que tende a manter os momentos magnéticos alinhados ao eixo principal dos NF. No cobalto com estrutura hexagonal compacta (hcp), os momentos magnéticos tendem a se alinhar em uma direção cristalina preferencial (eixo c), ou seja, há uma anisotropia magnetocristalina. Tal anisotropia é da mesma ordem de grandeza da anisotropia de forma de NF ideias (cujo comprimento é muito maior que o diâmetro). Nanofios de cobalto hcp são interessantes basicamente porque suas propriedades magnéticas dependerão fortemente da estrutura cristalina (tamanho do grão e orientação do cristal em relação ao eixo principal dos nanofios). Como as duas contribuições de anisotropia são da mesma ordem de grandeza, pode-se controlar a anisotropia efetiva ao longo do NF através do controle da direção cristalina. Neste trabalho foram produzidas redes de NF de Co via eletrodeposição em moldes de membrana nanoporosa de alumínio anodizado (MNPAA). Alterou-se a estrutura cristalina dos NF através do pH de eletrodeposição (1,9; 3,9 e 5,5). Os NF possuem diâmetro de 35 nm, comprimento de ~10 ?m e a distância entre eles na rede é de 110 nm . A estrutura cristalina foi estudada através de técnicas de microscopia eletrônica (de varredura e de transmissão) e por difração de raios-X. As propriedades magnéticas foram inferidas através de técnicas de magnetometria. Foram obtidas curvas de histerese em função da temperatura e do ângulo entre o campo magnético aplicado e o eixo principal dos NF. Também foram obtidas curvas de magnetização inicial com o campo aplicado paralelo e perpendicular aos NF, e após diferentes ciclos de desmagnetização. Também foram feitos alguns breves estudos sobre o efeito do tratamento térmico nas propriedades magnéticas dos NF; sobre a dieletroforese, que é uma técnica de separação dos NF removidos da MNPAA e dispersos em solução, e sobre as alterações morfológicas e grau de oxidação dos nanofios quando retirados da MNPAA. Observou-se que para pH¿s baixos o eixo c é perpendicular ao eixo principal e os grãos são pequenos. O aumento do pH tende a tornar o eixo c paralelo ao eixo principal dos nanofios, o que aumenta a anisotropia magnética efetiva da rede. O tamanho dos grãos também aumenta com o pH, tornando o meio cristalino local mais expressivo no processo de inversão da magnetização. Também se observou que, dependendo da direção do eixo c, a diminuição da temperatura pode inverter a direção fácil de anisotropia efetiva dos nanofios, devido ao aumento da anisotropia magnetocristalina / Abstract: Magnetic nanowire (NW) arrays have been attracting great attention due to their possible technological applications. Such arrays are promising candidates for different applications, such as spintronic devices, magnetic memory storage systems, magnetic field sensors and in several biological systems. On the other hand, from a basic science point of view, it is fundamental to understand the low dimensionality effect on materials magnetic properties. Many of the NW magnetic properties simply occur due to its elongated geometry. It creates a strong magnetic anisotropy which tends to maintain the magnetic moments aligned to the NW¿s main axis. In bulk cobalt with a hexagonal compact structure (hcp), the magnetic moments tend to align in a preferential crystalline direction, i.e. there is a magnetocrystalline anisotropy. Such anisotropy is of the same order of magnitude than NW¿s shape anisotropy (when the length is much bigger than the diameter). Hcp cobalt nanowires are mainly interesting because their magnetic properties strongly depend on their crystalline structure (grain size and crystal orientation with respect to the NW main axis). Since the two anisotropy contributions are of the same order of magnitude, we can control the effective anisotropy along the NW by controlling the crystalline structure orientation. In this study were produced Co NW arrays through eletrodeposition in aluminum nanoporous templates. The NW crystalline structure was altered by the pH during the eletrodeposition process. The NW present a diameter of 35 nm, length of ~10 ?m and an interwire distance of 110 nm. The crystalline structure was investigated through electronic microscopy techniques (scanning and transmission) and X-ray diffraction. The magnetic properties were inferred through magnetometry techniques. Hysteresis curves were obtained as a function of temperature and of the angle between the applied magnetic field and the NW¿s main axis. Initial magnetization curves with the applied field parallel and perpendicular to the NW, and after different demagnetization cycles, were also obtained. Finally, some brief studies have also been made about the effect of heat treatment on the NW magnetic properties; about dielectrophoresis, which is a separation technique for the NW removed from the alumina template and dispersed in solution; and about the morphological changes and the NW oxidation degree when removed from the alumina template / Mestrado / Física / Mestre em Física

Orientador: Marcelo Knobel / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T08:20:32Z (GMT). No. of bitstreams: 1 Duque_JoseGerivaldodosSantos_D.pdf: 2802085 bytes, checksum: 3e11d0645c4b8e47c4e251b671065013 (MD5) Previous issue date: 2005 / Resumo: Não informado / Abstract: Not informed. / Doutorado / Física da Matéria Condensada / Doutor em Ciências

The possibility to change magnetic anisotropy of amorphous TbCo films from out-of-plane to in-plane has been investigated. The effects of TbCo film's thickness and composition on the magnetic anisotropy were investigated together with the effects of growing the TbCo films on a SmCo seed layer. This was studied by sputtering TbCo films of composition Tb_xCo_(100-x) x=16,18,20,22 and 24, with thickness ranging between 2-20 nm, with and without the presence of a 20 nmSm_15Co_85 seed layer. All films were grown in a 130 mT magnetic in-plain field to imprint an in-plane anisotropy. The structure and composition of the films were examined with Rutherford backscattering spectrometry, X-ray reflectivity, and Grazing incidence X-ray diffraction. The magnetic properties of the films were studied with magneto-optic Kerr effect measurement, vibrating sample magnetometer, Kerr microscopy and magnetic force microscopy. The magneto-optic Kerr effect measurement showed that it was possible to change TbCo film's preferred magnetization direction from out-of-plane to in-plane by reducing the film thickness. The SmCo layer made it easier for theTbCo films to change preferred magnetization direction from out-of-plane to in-plane.

A collection of studies are reported that focus on the examination of exchange interactions in complexes containing paramagnetic ions with a large magnetic anisotropy. A number of complementary techniques are used to analyse the complicated systems that arise, including high-field high-frequency electron paramagnetic resonance, inelastic neutron scattering, SQUID magnetometry, and ab initio calculations. The nuclearity of the complexes ranges from dimetallic, to trimetallic, to octametallic. A family of five water- and carboxylate-bridged nickel(II) dimetallics are the focus of a magneto-structural correlation study that succeeds in measuring the magnitude of the exchange interaction despite dominating effects from large zero-field splitting effects. Similar work is reported for four cobalt(II) analogues of these compounds, with the relationship between exchange interactions and geometry also being probed by pressure INS. Charge density studies that combine high resolution X-ray and neutron diffraction studies are reported on cobalt and nickel analogues from the same family of dimetallics, revealing strong evidence for non-direct exchange. A family of four trimetallic triangle complexes containing two nickel(II) ions and one chromium(III) ion bridged by a central fluoride and a total of six carboxylates are reported, and the exchange interactions are elucidated from a global model that accounts for the low-field magnetic, heat capacity, and EPR data. Two new octametallic vanadium(III) wheels—where each pair of adjacent metals are bridged by a fluoride and two carboxylates—are reported along with preliminary results from magnetic measurements and solid state proton NMR spectra, which reveal significant field-dependent effects arising from level crossings at high fields.

Les effets de transfert de spin sont devenus un sujet de recherche majeur ces quinze dernières années. Cependant, un manque de vérifications expérimentales pour beaucoup de modèles décrivant les effets de transfert de spin peut être constaté. Ceci est surtout lié à un manque de systèmes magnétiques modèles permettant un contrôle précis des paramètres pertinents utilisés dans les modèles théoriques. Dans ce travail deux systèmes magnétiques à aimantation perpendiculaire ont été analysés : les alliages amorphes de Co1-xTbx élaborés par pulvérisation cathodique et les super-réseaux [Co/Ni](111) élaborés par épitaxie par jets moléculaires. L'anisotropie et l'aimantation, qui sont des paramètres pertinents dans beaucoup de modèles sur le transfert de spin, sont variables dans une large gamme. L'origine de cette anisotropie est discutée. La structure des domaines magnétiques est analysée et les résultats des mesures de transport sont interprétés. Pour les super-réseaux [Co/Ni](111) une forte polarisation en spin au niveau de Fermi est démontrée grâce à des expériences de photo émission résolue en spin et un coefficient d'amortissement intrinsèque [alpha] très faible est trouvé. Il est conclu que les alliages amorphes de Co1-xTbx et les super-réseaux [Co/Ni](111) sont des systèmes modèles pour le transfert de spin. / Spin transfer torque effects have become a research subject of high interest during the last 15 years. However, in order to probe the fundamental physics of spin transfer torque model systems are needed. For a model system it must be as simple as possible to tune the significant parameters (magnetic and structural). In this work we analyze the suitability of two materials for this need. The studied materials are amorphous Co1-xTbx alloys elaborated by sputtering and MBE grown [Co/Ni](111) superlattices. Both systems show perpendicular magnetic anisotropy (PMA), which provides a uniaxial anisotropy to the system. This anisotropy and the magnetization, which are significant parameters for many models on spin transfer torque, can be tuned in a large range of values. The origin of this PMA is discussed. The domain structure is analyzed and transport measurements are interpreted. In addition we show a strong spin polarization of the electrons close to the Fermi level by doing photoemission experiments. A small intrinsic Gilbert damping parameter [alpha] is found by FMR spectroscopy. We conclude that both materials are good candidates to be used as model systems for spin transfer torque

The temperature and field dependence of the magnetization of epitaxial, undoped anatase TiO2 thin films on SrTiO3 substrates was investigated. Low-energy ion irradiation was used to modify the surface of the films within a few nanometers, yet with high enough energy to produce oxygen and titanium vacancies. The as-prepared thin film shows ferromagnetism which increases after irradiation with low-energy ions. An optimal and clear magnetic anisotropy was observed after the first irradiation, opposite to the expected form anisotropy. Taking into account the experimental parameters, titanium vacancies as di-Frenkel pairs appear to be responsible for the enhanced ferromagnetism and the strong anisotropy observed in our films. The magnetic impurities concentrations was measured by particle-induced X-ray emission with ppm resolution. They are ruled out as a source of the observed ferromagnetism before and after irradiation.