<p>In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed.</p><p>The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L1₀ FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-<i>T</i>_C 3<i>d</i> transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4<i>f</i> spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level.</p>

In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed. The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L10 FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-TC 3d transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4f spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level.

Made available in DSpace on 2014-12-17T15:15:04Z (GMT). No. of bitstreams: 1 AnaKGA_DISSERT.pdf: 1807771 bytes, checksum: 5500fb357c9de3200037867308a2a9b6 (MD5) Previous issue date: 2014-07-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Iron nitrite films, with hundred of nanometers thick, were deposited using the Cathodic cage plasma nitriding method, with a N2/H2 plasma, over a common glass substract. The structure, surface morphology and magnetic properties were investigated using X-ray diffractometry (XRD), atomic force microscopy (AFM) and vibrating sample magnetometer (VSM). XRD shows the formation of &#947; FeN phase and a combination of &#950;Fe2N + &#603;Fe3N phases. The film s saturation magnetization and coercivity depends on morphology, composition, grain size and treatment temperature. Temperature raising from 250 ?C to 350 ?C were followed by an increase in saturation magnetization and film s surface coercivity on the parallel direction in relative proportion. This fact can be attributed to the grain sizes and to the different phases formed, since iron rich fases, like the &#603;Fe3N phase, emerges more frequently on more elevated treatment s temperature. Using this new and reasonably low cost method, it was possible to deposit films with both good adhesion and good magnetic properties, with wide application in magnetic devices / Filmes de nitreto de ferro, com centenas de nanometros de espessura foram depositados pelo m?todo de deposi??o/nitreta??o por Gaiola Cat?dica utilizando um plasma de N2/H2 sobre um substrato de vidro comum. A estrutura, morfologia da superf?cie e propriedades magn?ticas foram investigadas com o uso de Difratometria de Raio-X (DRX), Microscopia de For?a At?mica (MFA) e Magnet?metro de Amostra Vibrante (MAV). A DRX exibe a forma??o da fase &#947; FeN e mistura de fases &#950;Fe2N + &#603;Fe3N. A magnetiza??o de satura??o e coercividade dos filmes de nitreto de ferro dependem da morfologia, composi??o, tamanho de gr?o e temperatura de tratamento. Com o aumento da temperatura de 250 para 350 ?C, a magnetiza??o de satura??o e a coercividade na dire??o paralela ? superf?cie dos filmes tamb?m aumentam em propor??o relativa. Isto pode ser atribu?do aos tamanhos de gr?os e ?s diferentes fases formadas, j? que fases ricas em ferro como &#603;Fe3N surgem com frequ?ncia maior em temperaturas de tratamento mais elevadas. Neste estudo foi poss?vel a deposi??o de filmes de boa ades?o e boas propriedades magn?ticas com grande aplica??o em dispositivos magn?ticos por um m?todo novo e de baixo custo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work, we study the magnetic properties of CoFe2O4 nanoparticles dispersed in silica (SiO2) matrix. Samples were produced by the sol-gel method and synthesized at different temperatures. The average distance between the particles and thus the nature of inter-particle interactions were controlled for using different concentrations of iron and cobalt salts and the starting material tetraethylorthosilicate (TEOS). The samples were characterized by thermogravimetry (TG), X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetization as a function of magnetic field and temperature. Thermogravimetric analysis showed that the weight loss increases with increasing concentration of salts in the starting solution. The results of X-ray diffraction combined with the transmission electron microscope images confirmed the presence of CoFe2O4 nanoparticles dispersed into the SiO2 matrix. Magnetization measurements showed a typical behavior generally showed by a magnetic nanoparticles system, that is, the observation of a peak in the curve FC-ZFC with a thermal hysteresis in the low temperature region. In particular, we observed a dependence of the coercive field with temperature of CoFe2O4 nanoparticles that did not follow the predictions of the model Bean-Livingston. We believe that this fact is linked more to the effect of size distribution than the possible effects of interaction between the nanoparticles. In this regard, a model considering a particle size distribution in the coercivity of nanoparticles was used. The model was able to fit the experimental data to wide temperature range. / Neste trabalho, nós estudamos as propriedades magnéticas de nanopartículas de CoFe2O4 dispersas em uma matriz de sílica (SiO2). As amostras foram produzidas através do método sol-gel para diferentes temperaturas de síntese. A distância média entre as partículas e, deste modo, a natureza das interações inter-partículas foram controladas utilizando diferentes concentrações dos sais de ferro e cobalto e do reagente de partida tetraetilortossilicato (TEOS). As amostras foram caracterizadas através de medidas de termogravimetria (TG), fluorescência de raios X (FRX), difração de raios X (DRX), microscopia eletrônica de transmissão (MET) e magnetização em função do campo magnético e da temperatura. As análises termogravimétricas mostraram que a perda de massa aumenta com o aumento da concentração dos sais de partida na solução. Os resultados de difração de raios X combinados com as imagens de microscopia eletrônica de transmissão confirmaram a presença das nanopartículas de CoFe2O4 dispersas dentro da matriz de SiO2. As medidas de magnetização mostraram um comportamento típico de um sistema de nanopartículas magnéticas, ou seja, o aparecimento de um pico na curva de ZFC-FC com uma histerese térmica na região de baixas temperaturas. Em particular, nós observamos uma dependência do campo coercivo com a temperatura das nanopartículas de CoFe2O4 que não seguiu as previsões do modelo de Bean Livingston. Nós acreditamos que esse fato está ligado muito mais ao efeito da distribuição de tamanhos do que aos possíveis efeitos de interação entre as nanopartículas. Neste sentido, um modelo que considera a distribuição de tamanhos de partículas na coercividade das nanopartículas foi utilizado. O modelo foi capaz de ajustar os dados experimentais para amplo intervalo de temperatura.

Dans ce travail, nous nous intéressons à l’étude des propriétés structurales et magnétiques de films déposés sur des substrats de silicium et de verre, qui sont : Fe85Pd15, Fe80Pd20, Fe64Pd36 et Fe56Pd44, ainsi qu’aux corrélations qui peuvent être déduites de ces propriétés. Ces films minces sont élaborés par la technique d’évaporation thermique par effet Joule. Par ailleurs, ces films ont été analysés par plusieurs techniques, à savoir: la diffraction des rayons X (DRX), la microscopie électronique à balayage (MBE), la microscopie à force atomique (AFM), la spectrométrie Mössbauer, la magnétométrie SQUID, la magnétométrie à gradient de champ alternatif (AGFM) et la microscopie à force magnétique (MFM). L’analyse de DRX a révélé que les échantillons Fe80Pd20, Fe64Pd36 sont bi-phasiques et constitués d’une phase (Fe,Pd)-α cubique centrée (cc) et d’une phase FePd cubique à faces centrées (cfc). Par ailleurs, les échantillons Fe85Pd15 et Fe56Pd44 se sont avérés monophasiques et formés de la phase (Fe, Pd)-α, et de la phase FePd respectivement. Concernant les alliages, Fe85Pd15, Fe80Pd20et Fe64Pd36, nous avons trouvé, que la phase (Fe, Pd)-α se saturait à 20 % de Pd; et la phase ‘FePd’ apparaissait à ce même pourcentage. Ensuite, l’alliage Fe56Pd44 déposé sur le silicium a subit un recuit isotherme, à 550°C à différents temps de maintien, dans le but d’induire une transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. La variation, en fonction du temps, de la fraction transformée de la phase ordonnée, révélée par la DRX et le SQUID, s’est avérée obéir à la loi d’Avrami. Concernant les propriétés magnétiques, nous avons trouvé que l’alliage Fe64Pd36, était également le siège de la transformation de la phase FePd désordonnée en la phase L10FePd ordonnée. Cette transformation est marquée par l’existence d’un couplage d’échange entre la phase douce (Fe, Pd)-α et la phase dure L10FePd. Ce phénomène a été mis en évidence par plusieurs techniques révélant, par exemple, la forme du cycle d’hystérésis caractérisée par un champ coercitif élevé et une aimantation à saturation élevée. / In this work, we are interested in the study of the structural and magnetic properties of thin films deposited on silicon and glass substrates which are: Fe85Pd15, Fe80Pd20, Fe64Pd36 and Fe56Pd44, as well as in the correlations which can be deduced from these properties. These thin films are prepared using the thermal evaporation technique by Joule effect. Moreover, these films have been analyzed by several techniques, namely: X-rays diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Mössbauer spectrometry, SQUID magnetometer, alternating field gradient magnetometer (AFGM) and magnetic force microscopy (MFM). The XRD analysis revealed that the Fe80Pd20 and Fe64Pd36 samples are biphasic, and present a body centered cubic (bcc) α-(Fe, Pd) and a face centered cubic (fcc) FePd structure respectively. Furthermore, the samples Fe85Pd15 and Fe56Pd44 were observed to be monophasic and formed of a body centered cubic α-(Fe, Pd) phase and a face centered cubic FePd phase respectively. Concerning the Fe85Pd15, Fe80Pd20 and Fe64Pd36 alloys, we found that the α-(Fe, Pd) phase saturated at 20% of Pd and that the FePd phase appeared at this same concentration. Then, the Fe56Pd44 alloy deposited on silicon substrates was subjected to isothermal annealing, at 550 ° C for different holding times, in order to induce a transformation of the disordered FePd phase into the ordered L10FePd phase. The variation, as a function of time, of the transformed fraction of the ordered phase, revealed by XRD and SQUID, was found to obey to Avrami's law. Concerning the magnetic properties, we have found that the Fe64Pd36 alloy was also observed to present a transformation of the disordered FePd phase into the ordered L10FePd phase. This transformation is marked by the existence of an exchange coupling between the soft α-(Fe, Pd) phase and the hard L10FePd phase. This phenomenon has been confirmed by several techniques revealing, for instance, the shape of the hysteresis cycle characterized by a high coercive field and a high saturation magnetization.

O presente trabalho avaliou o efeito de tratamentos térmicos ou diferentes graus de deformação plástica na transformação da austenita do microconstituinte AM de uma chapa de aço alta resistência baixa liga (ARBL) classe API 5L X80 usada para gasodutos. A chapa tem espessura de 19 mm e passaria pelo processo de conformação UOE, mas a deformação foi realizada por laminação a frio, a temperatura ambiente, com reduções de 5 a 20%. O propósito foi compreender melhor o microconstituinte AM, explorar a transformação martensítica induzida por deformação (SIMT) e a decomposição austenítica por tratamento térmico, com ênfase em seu comportamento magnético. A transformação da austenita foi acompanhada através de medidas de polarização magnética, comparada com a densidade de massa e difração de raios X. A deformação plástica e os tratamentos térmicos alteraram a polarização magnética de saturação e a densidade de massa da amostra de aço de forma compatível com a eliminação da austenita retida metaestável. O método de densidade hidrostática foi considerado sensível para mensurar transformações de fase. Os dados obtidos revelam expansão volumétrica de aproximadamente 0,13%, correspondendo a 3,2% a quantidade de austenita retida original do material, enquanto os valores obtidos por polarização magnética de saturação são 2,8% pelo histeresígrafo e 2,1% por MAV. A difração de raios X nas amostras sob deformação ou tratamentos térmicos resultaram em queda nos primeiros picos da austenita quando comparadas com a amostra como recebida. / This study evaluated the effect of different degrees of plastic deformation or heat treatment on the transformation of austenite into martensite of an HSLA steel plate API 5L X80 for pipelines. A 19 mm thickness plate would be submitted to UOE forming process, but the cold work instead occurred by cold rolling at room temperature, with reductions of 5 up to 20%. The purpose was to better understand the MA constituent, explore the strain-induced martensitic transformation (SIMT) and austenitic decomposition by heat treatment with emphasis on its magnetic behavior. The transformation was accompanied by saturation magnetization measurements, compared with the mass density and X-ray diffraction. The plastic deformation or the heat treatment altered the saturation magnetization and the mass density in a manner consistent with the elimination of metastable retained austenite. The density method is sensible to measure phase transformations induced by strain. The data obtained shows a volumetric expansion of about 0.13%, corresponding to an amount of retained austenite of the original material of 3.2%, while the values obtained by magnetization saturation are 2.8% by hysteresigraph and 2.1% by VSM. By X-ray diffraction there is a clear drop in first peaks of austenite of the samples under deformation or heat treatment compared with the sample as-received.

The hole-doped perovskite manganese oxide such as Ln1-xAxMnO3 (Ln = La, Nd, Pr, and A = Ca, Sr, Ba, Pb) is one of the most studied topics in the recent years due to the observation of colossal magnetoresistance (CMR). Basically, LaMnO3 has an almost insulating behavior and on antiferromagnetic arrangement. By substituting a divalent cation (A2+) in place of La3+, LaMnO3 can be driven into metallic and ferromagnetic state. Mixed valence of Mn 3+ / Mn4+ is needed for both metallic behavior and ferromagnetism in these materials. The CMR characteristic occurs in the ferromagnetic state. A systematic investigation of the structural, magnetic and electrical properties in the perovskite colossal magnetoresistance materials La0.7-xLnxPb0.3Mn1-yMeyO3 (Ln=Pr, Nd and Y, Me=Fe and Co) has presented in this thesis. By subatituting Nd, Pr, Y for the La and Co, Fe for the Mn, the substitution effects on the crystallographic deformation, magnetotransport behavior and electrical properties in these compounds have been studied. According to the results of this research, crystallographic distortion is induced by the substitution of smaller ions, Pr or Nd, onto the La-site. Powder $x$-ray diffraction patterns show a crystallographic transition from rhombohedral symmetry (R-3c) to orthorhombic (Pbnm) crystal structure as the doping content is increased. The increase of deformation from R-3c to Pbnm decreases the bond angle of Mn3+¡ÐO2-¡ÐMn4+ , increases the cant of Mn spin, weakens the double-exchange interaction and results in decrease of ferromagnetism, low ferromagnetic transition temperature Tc, eg electron bandwidth and conductivity. However, the great quantity of decrease in resistivity by an external field leads to the increase in the magnetoresistance ratio. We also find that the increase of saturation magnetization results from the contribution of magnetic ion of Pr or Nd. In addition. in contrast to substitution La by magnetic ion of Pr and Nd, the saturation magnetization is decreased as Y content is increased. The zero-field-cool (ZFC) and field-cool (FC) magnetic measurements indicate that the range of spin ordering for Y one is shorter than Pr one or Nd one with the same doping content. It is because of the small ionic radius of Y, which results in larger distortion, increases the bond angle of Mn3+¡ÐO2-¡ÐMn4+, and corresponds low ferromagnetic transition temperature. The distortion induced by Mn-site substitution is not obvious due to the similar radius of Mn, Co and Fe. Powder x-ray diffraction patterns show a single phase of rhombohedral symmetry (R-3c) for Co doped ststem and a slight crystallographic transition from rhombohedral (R-3c) to orthorhombic (Pbnm) symmetry for Fe doped system. Values of temperature dependence of magnetization indicate that the ferromagnetic double-exchange interaction is gradually substituted by the superexchange interaction. The ZFC-FC curves also indicate that long-range spin ordering is progressively substituted by the short-range spin ordering. The substitution of Mn by Co and Fe supresses the double-exchange interaction, decreases the ferromagnetism and the ferromagnetic transition temperature. Due to the synthesis of the substitution of Nd, Pr, Y for La and Co, Fe for Mn, the mechanism of substitution effects are proved different. The substitution of Nd, Pr and Y for La distorts the crystal, decreases the Mn3+¡ÐO2-¡ÐMn4+ bond angle, and results in the transition of properties, while the substitution of Co and Fe for Mn decrease the percentage of ferromagnetic Mn3+¡ÐO2-¡ÐMn4+. The purpose of this thesis is to clear up the role functions of all elements in these compounds and properties of these compounds. Based on the knowledge of these compounds, it would be helpful to control the physical mechanism and improve the characteristics on preparing their thin film devices.

O presente trabalho avaliou o efeito de tratamentos térmicos ou diferentes graus de deformação plástica na transformação da austenita do microconstituinte AM de uma chapa de aço alta resistência baixa liga (ARBL) classe API 5L X80 usada para gasodutos. A chapa tem espessura de 19 mm e passaria pelo processo de conformação UOE, mas a deformação foi realizada por laminação a frio, a temperatura ambiente, com reduções de 5 a 20%. O propósito foi compreender melhor o microconstituinte AM, explorar a transformação martensítica induzida por deformação (SIMT) e a decomposição austenítica por tratamento térmico, com ênfase em seu comportamento magnético. A transformação da austenita foi acompanhada através de medidas de polarização magnética, comparada com a densidade de massa e difração de raios X. A deformação plástica e os tratamentos térmicos alteraram a polarização magnética de saturação e a densidade de massa da amostra de aço de forma compatível com a eliminação da austenita retida metaestável. O método de densidade hidrostática foi considerado sensível para mensurar transformações de fase. Os dados obtidos revelam expansão volumétrica de aproximadamente 0,13%, correspondendo a 3,2% a quantidade de austenita retida original do material, enquanto os valores obtidos por polarização magnética de saturação são 2,8% pelo histeresígrafo e 2,1% por MAV. A difração de raios X nas amostras sob deformação ou tratamentos térmicos resultaram em queda nos primeiros picos da austenita quando comparadas com a amostra como recebida. / This study evaluated the effect of different degrees of plastic deformation or heat treatment on the transformation of austenite into martensite of an HSLA steel plate API 5L X80 for pipelines. A 19 mm thickness plate would be submitted to UOE forming process, but the cold work instead occurred by cold rolling at room temperature, with reductions of 5 up to 20%. The purpose was to better understand the MA constituent, explore the strain-induced martensitic transformation (SIMT) and austenitic decomposition by heat treatment with emphasis on its magnetic behavior. The transformation was accompanied by saturation magnetization measurements, compared with the mass density and X-ray diffraction. The plastic deformation or the heat treatment altered the saturation magnetization and the mass density in a manner consistent with the elimination of metastable retained austenite. The density method is sensible to measure phase transformations induced by strain. The data obtained shows a volumetric expansion of about 0.13%, corresponding to an amount of retained austenite of the original material of 3.2%, while the values obtained by magnetization saturation are 2.8% by hysteresigraph and 2.1% by VSM. By X-ray diffraction there is a clear drop in first peaks of austenite of the samples under deformation or heat treatment compared with the sample as-received.

In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer films have been investigated with the main objective of finding a way to determine their saturation magnetization. Both polar magneto-optical Kerr effect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine µ0MS, circumventing the problem of the unknown effective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high fluences. Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and fitting software. With both increasing ion fluence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10×Py samples, an immediate decrease of µ0MS already sets in at small ion fluences. However, for the 1×Py and 5×Py samples, the saturation magnetization remains constant up to a certain ion fluence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical fluence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10–15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaffected by the ion fluence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter α increases with both increasing number of Py/Ta interfaces and higher ion fluences, with the former having a stronger influence. The inhomogeneous linewidth broadening ΔB0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion fluences. / In dieser Dissertation ist der Einfluss von Ionenbestrahlung auf die magnetostatischen und dynamischen Eigenschaften von weichmagnetischen Py/Ta-Einzel- und Multilagen (Py = Permalloy: Ni80Fe20) untersucht worden, wobei das Hauptziel gewesen ist, eine Methode zur Bestimmung der Sättigungsmagnetisierung zu finden. Sowohl polare magneto-optische Kerr-Effektmessungen (MOKE) als auch ferromagnetische Resonanzmessungen mittels eines Vektornetzwerkanalysators (VNA-FMR) haben sich als geeignet erwiesen, um µ0MS zu bestimmen, wobei das Problem des unbekannten effektiven magnetischen Volumens umgangen wird, welches bei der Verwendung von Techniken wie SQUID oder VSM auftreten würde. Unter der Voraussetzung, dass die Proben keinen senkrechten magnetischen Anisotropiebeitrag besitzen, kann die Sättigungsmagnetisierung selbst im Fall starker Grenzflächendurchmischung infolge einer großen Anzahl an Py/Ta-Grenzflächen und/oder Ionenbestrahlung mit hohen Fluenzen bestimmt werden. Ein weiterer wesentlicher Bestandteil dieser Arbeit ist die Konstruktion eines VNA-FMR-Spektrometers gewesen, welches vollautomatisiert ist, polare und azimutale Winkelabhängigkeiten messen kann und einen Magneten besitzt, der Proben, die Eisen beinhalten, sättigen kann. Von Grund auf beginnend umfasste dies zahlreiche Schritte wie z. B. die Entwicklung eines geeigneten koplanaren Wellenleiterdesigns sowie das Schreiben von Steuerungs-, Auswertungs- und Fitprogrammen. Mit steigender Fluenz und Zahl an Py/Ta-Grenzflächen ist eine Abnahme der Sättigungsmagnetisierung beobachtet worden. Im Fall der 10×Py-Proben findet diese bereits bei kleinen Fluenzen statt. Im Gegensatz dazu bleibt µ0MS der 1×Py- und 5×Py-Proben bis zu einer bestimmten Fluenz konstant, bevor sie sich dann umso schneller verringert. Die Bestrahlung mit Ne-Ionen verursacht eine Durchmischung und Verbreiterung der Grenzflächen. Infolgedessen erfahren die Py/Ta-Proben bei einer kritischen Fluenz, die von der Zahl der Grenzflächen abhängig ist, einen Phasenübergang von polykristallin zu amorph. Die Sättigungsmagnetisierung verschwindet ab einer Ta-Konzentration von etwa 10–15 Atom-% in den Py-Schichten. Die Proben besitzen eine kleine uniaxiale Anisotropie, die praktisch unbeeinflusst von der Fluenz ist, sich jedoch mit steigender Zahl an Py/Ta-Grenzflächen leicht verringert. Neben den statischen sind auch die dynamischen magnetischen Eigenschaften der Proben untersucht worden. Der Gilbert-Dämpfungsparameter α erhöht sich sowohl mit steigender Zahl an Py/Ta-Grenzflächen als auch mit höheren Fluenzen, wobei Erstere einen größeren Einfluss hat. Die inhomogene Linienverbreiterung ΔB0 nimmt ebenfalls mit steigender Zahl an Py/Ta-Grenzflächen zu, verringert sich jedoch bei größeren Fluenzen leicht.

In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer films have been investigated with the main objective of finding a way to determine their saturation magnetization. Both polar magneto-optical Kerr effect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine µ0MS, circumventing the problem of the unknown effective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high fluences. Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and fitting software. With both increasing ion fluence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10×Py samples, an immediate decrease of µ0MS already sets in at small ion fluences. However, for the 1×Py and 5×Py samples, the saturation magnetization remains constant up to a certain ion fluence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical fluence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10–15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaffected by the ion fluence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter α increases with both increasing number of Py/Ta interfaces and higher ion fluences, with the former having a stronger influence. The inhomogeneous linewidth broadening ΔB0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion fluences. / In dieser Dissertation ist der Einfluss von Ionenbestrahlung auf die magnetostatischen und dynamischen Eigenschaften von weichmagnetischen Py/Ta-Einzel- und Multilagen (Py = Permalloy: Ni80Fe20) untersucht worden, wobei das Hauptziel gewesen ist, eine Methode zur Bestimmung der Sättigungsmagnetisierung zu finden. Sowohl polare magneto-optische Kerr-Effektmessungen (MOKE) als auch ferromagnetische Resonanzmessungen mittels eines Vektornetzwerkanalysators (VNA-FMR) haben sich als geeignet erwiesen, um µ0MS zu bestimmen, wobei das Problem des unbekannten effektiven magnetischen Volumens umgangen wird, welches bei der Verwendung von Techniken wie SQUID oder VSM auftreten würde. Unter der Voraussetzung, dass die Proben keinen senkrechten magnetischen Anisotropiebeitrag besitzen, kann die Sättigungsmagnetisierung selbst im Fall starker Grenzflächendurchmischung infolge einer großen Anzahl an Py/Ta-Grenzflächen und/oder Ionenbestrahlung mit hohen Fluenzen bestimmt werden. Ein weiterer wesentlicher Bestandteil dieser Arbeit ist die Konstruktion eines VNA-FMR-Spektrometers gewesen, welches vollautomatisiert ist, polare und azimutale Winkelabhängigkeiten messen kann und einen Magneten besitzt, der Proben, die Eisen beinhalten, sättigen kann. Von Grund auf beginnend umfasste dies zahlreiche Schritte wie z. B. die Entwicklung eines geeigneten koplanaren Wellenleiterdesigns sowie das Schreiben von Steuerungs-, Auswertungs- und Fitprogrammen. Mit steigender Fluenz und Zahl an Py/Ta-Grenzflächen ist eine Abnahme der Sättigungsmagnetisierung beobachtet worden. Im Fall der 10×Py-Proben findet diese bereits bei kleinen Fluenzen statt. Im Gegensatz dazu bleibt µ0MS der 1×Py- und 5×Py-Proben bis zu einer bestimmten Fluenz konstant, bevor sie sich dann umso schneller verringert. Die Bestrahlung mit Ne-Ionen verursacht eine Durchmischung und Verbreiterung der Grenzflächen. Infolgedessen erfahren die Py/Ta-Proben bei einer kritischen Fluenz, die von der Zahl der Grenzflächen abhängig ist, einen Phasenübergang von polykristallin zu amorph. Die Sättigungsmagnetisierung verschwindet ab einer Ta-Konzentration von etwa 10–15 Atom-% in den Py-Schichten. Die Proben besitzen eine kleine uniaxiale Anisotropie, die praktisch unbeeinflusst von der Fluenz ist, sich jedoch mit steigender Zahl an Py/Ta-Grenzflächen leicht verringert. Neben den statischen sind auch die dynamischen magnetischen Eigenschaften der Proben untersucht worden. Der Gilbert-Dämpfungsparameter α erhöht sich sowohl mit steigender Zahl an Py/Ta-Grenzflächen als auch mit höheren Fluenzen, wobei Erstere einen größeren Einfluss hat. Die inhomogene Linienverbreiterung ΔB0 nimmt ebenfalls mit steigender Zahl an Py/Ta-Grenzflächen zu, verringert sich jedoch bei größeren Fluenzen leicht.