Dissertations / Theses on the topic 'Nickel zinc ferrite'

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
FundaÃÃo de Amparo à Pesquisa do Estado do CearÃ
Nos Ãltimos anos, um grande interesse na associaÃÃo de materiais magnÃticos e biolÃgicos tem sido relatado na literatura. A obtenÃÃo de novos compÃsitos constituÃdos de galactomanana (GM), nanopartÃculas magnÃticas (MNPs) de NiZn e glicerol (GL) foram produzidos em diferentes proporÃÃes com finalidade de potencializar as caracterÃsticas individuais de cada material para futuras aplicaÃÃes. Sendo assim, as propriedades estruturais, magnÃticas e dielÃtricas dos nanobiocompÃsitos foram investigadas por DifraÃÃo de Raios-X (DRX), Espectroscopia de AbsorÃÃo na RegiÃo de Infravermelho (FTIR), AnÃlise TÃrmica (TG), Calorimetria ExploratÃria Diferencial (DSC), Microscopia EletrÃnica de Varredura (MEV), Microscopia EletrÃnica de TransmissÃo (TEM), Medidas MagnÃticas e Medidas DielÃtricas. A estrutura de espinÃlio da ferrita de NiZn foi confirmada por DRX e TEM e a amostra GMGL apesar de ser um material amorfo apresentou em seus nanobiocompÃsitos picos caracteristicos da fase de NiZn. As bandas caracterÃsticas para as amostras foram confirmadas por FTIR. Estas por sua vez seguiram um perfil de degradaÃÃo de acordo com as quantidades de NiZn incorporados, confirmados nos termogramas de DSC. A caracterizaÃÃo por MEV foi importante para avaliaÃÃo da morfologia. Os resultados das medidas dielÃtricas apresentaram baixas perdas dielÃtricas e das medidas magnÃticas mostraram comportamento magnÃtico para todos os nanobiocompÃsitos. Portanto, os resultados da caracterizaÃÃo dos nanobiocompÃsitos foram satisfatÃrios para possÃveis aplicaÃÃes como biomaterias, dispositivos eletrÃnicos ou em Ãreas afins.
In recent years, a great interest in the association of magnetic and biological materials has been reported in the literature. New composite consisting of galactomannan (GM), magnetic nanoparticles (NPs) of NiZn and glycerol (GL) were produced in different proportions with the purpose of enhancing the individual characteristics of each material for future applications. Thus, the structural, magnetic and dielectric properties of nanobiocomposites were investigated by Absorption Spectroscopy in the Region of Infrared (FTIR), X-Ray Diffraction (XRD), Thermal Analysis (TG), Differential Scanning Calorimetry (DSC), Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Magnetic Measurements and Dielectric Measurements. The structure of spinel NiZn ferrite was confirmed by XRD and TEM. Sample GMGL despite being an amorphous material presented in their nanobiocomposites characteristic peaks of phase NiZn. The characteristic bands in the samples were confirmed by FTIR. These in turn followed a degradation profile in accordance with the amounts of NiZn incorporated, which was confirmed in the DSC thermograms. The characterization by SEM was important to assess the morphology. The results of dielectric measurements showed low dielectric loss and magnetic measurements showed magnetic behavior for all nanobiocomposites. Therefore, the results of the characterization of nanobiocomposites were satisfactory for potential applications as biomaterials, electronic devices or related areas.

Nickel zinc ferrites (NZF) have been considered as one of the basic components in high frequency electromagnetic applications especially in the field of telecommunications. In the present study, the aim was to produce high quality nickel zinc ferrite ceramics at low soaking temperatures. For this purpose, conventional ceramic manufacturing method based on mixed oxide precursors was followed using calcium fluoride, CaF2, as sintering additive. During the sintering studies, it was noticed that both the microstructure and the electromagnetic properties of the NZF ceramics were modified to a great extent by CaF2. Therefore, material characterization studies involving microstructural, dielectric and magnetic properties were conducted with respect to CaF2 content of ceramics and soak duration. The results showed that due to the presence of CaF2 in ceramics, significant improvements were achieved not only in kinetics of sintering but also in the parameters
DC electrical resistivity, dielectric constant and dielectric loss factor. For example, 1.0 wt% CaF2 added NZF ceramic produced in this study had a DC electrical resistivity of 1011 &
#61527
-cm which was 100,000 times bigger than the one attained in pure NZF ceramic. On the other hand, the dielectric constant exhibited a flat behavior up to 40 MHz with a value around 16. In addition, no resonance peak was observed in dielectric loss factor spectra, and the typical values of dielectric loss factor lied below 0.01. Besides the achievements mentioned, the magnetic properties such as relative magnetic loss factor and hysteresis parameters were also improved.

This investigation was initiated by IBM to determine the types of cracks formed in hot-isostatic-pressed (HIP) Ni-Zn ferrite under impact and static loading conditions. A 1/8-inch tungsten carbide (WC) ball was used to apply the load in both cases. The impact loading condition was accomplished by dropping the WC ball from various heights between 40 and 200 cm. The static loading condition was accomplished by applying loads of 10 kg, 15 kg, and 30 kg on a Rockwell Hardness Tester. The response of HIP Ni-Zn ferrite to impact and static loading was elastic/plastic yielding permanent indentations. "Dimple" impressions, Hertzian-ring cracks, and radial cracks were formed upon applying increasing loads to the HIP Ni-Zn ferrite. As the grain size of the material was increased, both the Hertzian-ring and radial cracks were formed at lower loads compared to the as-received samples. The "dimple" impressions were not observed to follow this trend.

The ferrites are a wide class of ferrimagnetic materials with great technological importance and are studied extensively for many decades. Their remarkable magnetic characteristics make it an element often used in induction transformers by his high magnetic permeability, high values of saturation magnetization and low coercivity, resulting in smaller losses in their hysteresis loops. In this work were characterized pure nickel ferrite (NiFe2O4), a soft magnetic material where the magnetic properties depend on the nature of the ions, their charges and their distribution among the tetrahedral and octahedral sites. Heat treatment and sintering time were emphasized. In order to improve one of the most important parameters for such an application, the saturation magnetization, new samples were doped with zinc at various concentrations (Ni1-xZnxFe2O4). Two new series were prepared starting from the higher value of the previous series (Ni0,6Zn0,4Fe2O4) with two new doping, indium and gadolinium. Finally, the values of saturation magnetization and initial permeability could be compared with samples of commercial cores, showing the potential of the compound to be used as the core of magnetic induction.
As ferritas formam uma ampla classe de materiais ferrimagnéticos com grande importância tecnológica e têm sido estudadas exaustivamente ao longo de décadas. Suas notáveis características magnéticas as tornam um elemento frequentemente utilizado em transformadores de indução por sua alta permeabilidade magnética, altos valores de magnetização de saturação e baixa coercividade, resultando em perdas menores observadas em seus ciclos de histerese. Neste trabalho foram caracterizadas ferritas de níquel pura (NiFe2O4), um material magnético mole onde as propriedades magnéticas dependem da natureza dos íons, suas cargas e sua distribuição entre os sítios tetraédricos e octaédricos. Nessa fase o tratamento térmico e o tempo de sinterização tiveram ênfase. A fim de melhorar um dos parâmetros mais importantes para tal aplicação, a magnetização de saturação, foram feitas novas amostras dopadas com zinco em várias concentrações (Ni1-xZnxFe2O4). Duas novas séries foram preparadas partindo-se do maior valor da série anterior (Ni0,6Zn0,4Fe2O4) com dois novos dopantes, o índio e o gadolínio. Finalmente, os valores de magnetização de saturação e permeabilidade inicial puderam ser comparados com amostras de núcleos comerciais, evidenciando a potencialidade do composto em ser utilizado como núcleo de indução magnética.

La miniaturisation des antennes s'accompagne d'une dégradation leurs performances (bande passante, gain, efficacité), surtout avec l'utilisation de substrats matériaux diélectriques. Pour relever le défi « intégration / performances », la conception de nouveaux matériaux tels que les ferrites magnétoélectriques constitue une alternative des plus prometteuses. Ce travail met en avant les principaux paramètres à l'élaboration de ferrite spinelle par coprécipitation. Un traitement thermique modéré a permis l'obtention de céramiques semi poreuses pour la montée en fréquence. En parallèle, l'anisotropie magnétocristalline, liée à la composition (rapport Nickel / Zinc, Cobalt, Fer 2+…) ; ainsi que l'anisotropie magnétoélastique lors de l'application d'une contrainte, étendent encore le domaine des faibles pertes des ferrites de Nickel-Zinc de 400 MHz à plus de 1 GHz. Ces matériaux ont ainsi pu équiper des antennes sur les fréquences du DVH-H (470 – 830 MHz) et répondent aux normes du DVB-H. De façon à profiter pleinement de la miniaturisation, nous avons proposé une antenne imprimée. Une bonne corrélation est trouvée entre les résultats de simulation et de mesure, ainsi que des relations adaptées aux antennes patch. Enfin dans le domaine émergent des communications On / Off bodies, nous avons développé des antennes flexibles sur un substrat de type PDMS. Pour assurer une bonne efficacité de l'antenne, celle-ci est encapsulée, ce qui évite une métallisation hasardeuse (fissures, manque d'adhérence)
Antenna miniaturization, especially with dielectric substrates, is accompanied by a radiation loss (bandwidth, gain, efficiency). To meet the challenge "integration / performance", the design of new materials such as magnetodielectrics ferrites is a promising alternative. To satisfy these requirements, this work highlights the main parameters of ferrite spinel development by coprecipitation. A moderate thermal treatment leads to semi porous ceramics. In parallel, the magnetocrystalline anisotropy, related to the composition (ratio Nickel / Zinc, Cobalt, Iron 2+ ...), and the magnetoelastic anisotropy with application of stress, extend the field of low-loss from 400 MHz to over 1 GHz, in the Nickel-Zinc ferrite. These materials were able to equip antennas on DVH-H frequencies (470-830 MHz). In order to take full advantage of miniaturization, we proposed a printed antenna. A good correlation between simulation results and measurement is obtained, together with relations adapted to patch antennas. Finally, in the emerging field of communications On / Off bodies, we have developed flexible antennas on PDMS substrate. To ensure good antenna efficiency, it is encapsulated, thereby avoiding a hazardous metallization (cracks, loss of adhesion)

Im Rahmen dieser Arbeit wurde der Einfluss von Defekten auf die Eigenschaften von Ferrit-Dünnfilmen untersucht. Die Dünnfilme wurden mit Hilfe von gepulster Laserabscheidung bei verschiedenen Züchtungsparametern hergestellt. Durch Variation der Substrattemperatur und des Sauerstoffpartialdrucks wurden Dünnfilme verschiedener kristalliner Qualität gezüchtet. Diese wurden hinsichtlich ihrer chemischen Komposition mit Hilfe von energie-dispersiver Röntgenspektroskopie und Röntgenphotoelektronenspektroskopie untersucht. Durch Korrelation der Ergebnisse mit Messungen zum zirkularen magnetischen Röntgendichroismus, konnte eine partielle Inversion der Spinellstruktur nachgewiesen werden. Der Grad der Inversion ist höher für geringe Abscheidetemperaturen. Für diese defektreichen Dünnfilme zeigen Röntgenbeugungsuntersuchungen eine geringere kristalline Ordnung der Dünnfilme. Die strukturellen Defekte haben einen maßgeblichen Einfluss auf die elektrischen und magnetischen Eigenschaften der Ferrit-Dünnfilme. So zeigen die Ferrit-Dünnfilme für geringe Züchtungstemperaturen eine erhöhte elektrische Leitfähigkeit, während Dünnfilme, die bei hohen Substrattemperaturen gezüchtet wurden, isolierend sind. Die Temperaturabhängigkeit der elektrischen Leitfähigkeit kann auf thermisch aktivierte Hopping-Leitung oder die Leitung zwischen Clustern, die in einer Matrix eingebettet sind, zurückgeführt werden. Die magnetischen Eigenschaften von Zinkferrit-Dünnfilmen werden maßgeblich durch Defekte in der Spinellstruktur bestimmt, da es nominell in der normalen Spinellstruktur kristallisiert und daher antiferromagnetisch ist. Die partielle Inversion der Eisen- und Zinkionen führt zu Ferrimagnetismus in den Zinkferrit-Dünnfilmen, der mit Hilfe von SQUID-Messungen in dieser Arbeit eingehend untersucht wurde. Durch Korrelation der Ergebnisse der verschiedenen Untersuchungsmethoden konnten Rückschlüsse auf die dominierenden Defekte in den Ferrit-Dünnfilmen geschlossen werden. So sind zum einen Defekte auf atomarer Skala, wie Antisite-Defekte und divalenten Fe-Ionen für die erhöhte elektrische Leitfähigkeit und die größere Magnetisierung der defektreichen Dünnfilme verantwortlich. Zum anderen können ausgedehnte Defekte, im Speziellen Cluster, die in einer amorphen Matrix eingebettet sind, nicht ausgeschlossen werden.

Afin d'ameliorer les proprietes absorbantes des ferrites spinelles ni-zn, des plaquettes de composition chimique ni#0#,#4#5zn#0#,#5#5fe#2o#4 ont ete synthetisees selon deux methodes: la premiere est une reaction en sels fondus a partir de fe#2o#3 micace en poudre et permet d'obtenir des plaquettes de 10 a 30 microns, la seconde est une reaction d'echange a partir de kfe#1#1o#1#7 monocristallin et permet d'obtenir des plaquettes de 50 microns a plusieurs millimetres. Grace a une technique de mesure en ligne coaxiale, on a mesure la permeabilite complexe des plaquettes de ferrite spinelle en fonction de la frequence sur des ceramiques et des echantillons monocristallins

Waste water containing high concentrations of dissolved metals were delivered to the environmental company SAKAB. After standard treatment procedure, involving regulation of pH and addition of flocculation agents, the water still contained nickel concentrations of 26 mg/l. Since SAKAB’s regulatory concentration limit value for nickel in outgoing water is 0.5 mg/l, further treatment was necessary. According to the supplier of the water, a complexing agent similar to EDTA had been added to the water. The aim of this study was to decrease concentrations of nickel, zinc and copper. One part of this study was the precipitation experiments as hydroxide, sulphide and adsorption to hydrous ferric oxide. The other part was adsorption to natural, organic materials such as peat, wood chips and one commercial bark compost. Adsorption to hydrous ferric oxide was the most efficient of the precipitation experiments. When 2000 mg FeCl3 was added to 100 ml waste water and pH of the solution was adjusted to pH 8, a decrease up to 74 % of total nickel concentrations was achieved. Most efficient of the adsorption experiments were the one with commercial bark compost which decreased nickel concentrations in solution up to 94 % after 20 hours of agitation.

碩士
東海大學
化學工程與材料工程學系
103
In this study, we reported on the surface micro-structure, component analysis, electrical impedance, and surface roughness of cobalt doped nickel-zinc ferrites (Ni0.5Zn0.5-xCoxFe2O4, x = 0.1, 0.2, 0.3, 0.4, 0.5). Ferrites were prepared by solid state and sol-gel methods and mixed with acrylic resin for spin coating and with epoxy resin for hot pressing. The surface micro-structure does not change obviously with doping amount of cobalt. The cobalt atomic % increases with doping amount of cobalt, but the zinc atomic % decreases with doping amount of cobalt. The real part of electrical impedance of sample prepared by hot pressing is higher than that of sample prepared by spin coating. The real part shift of electrical impedance of Ni0.5Zn0.4Co0.1Fe2O4 prepared by solid state method mixed with epoxy resin for hot pressing is more close to that of reference. The real part shift of electrical impedance increases with the doping amount of cobalt. The imaginary part of electrical impedance of sample prepared by hot pressing is higher than that of sample prepared by spin coating. The imaginary part shift of electrical impedance of Ni0.5Co0.5Fe2O4 prepared by solid state method mixed with epoxy resin for hot pressing is more close to that of reference. The imaginary part shift of electrical impedance decreases with the doping amount of cobalt. The surface roughness does not change obviously with doping amount of cobalt. The surface roughness of ferrite prepared by sol-gel method mixed with epoxy for hot pressing increases with the doping amount of cobalt.

碩士
元智大學
化學工程學系
92
Carbon dioxide is the main greenhouse gas and plays a role in the greenhouse effect. Therefore, the decomposition of CO2 over Ni- or Zn-ferrite nanoparticles and the oxidation states or fine structures of Fe species in nanophase Ni- or Zn-ferrite catalysts by XRD, FE-SEM, TEM, XANES and EXAFS spectroscopies were investigated. The reactions of CO2 decomposition were conducted with nanopahse Zn- or Ni-ferrites at T = 573 K (P = 1 atm) and the gaseous products were determined by on-line GC/TCD. The nanophase Ni- or Zn-ferrites with optimally 2-hr hydrogenation were highly effective in decomposing CO2 to C and O2 with little or no CO formation in a few seconds or minutes. This complete decomposition of CO2 may be possible through the use of nanophase Ni- or Zn-ferrites because their surface-to-volume ratio was very high. When CO2 contacts with oxygen deficient ferrites, decomposition of CO2 may occur by the incorporation of O anions in the vacancies and deposition of carbon on the surface. The carbon on the surface may be converted to methane (methanation) upon treatment with H2 (hydrogenation) while regenerating used ferrite to oxygen deficient ferrite. The preedge XANES spectra of Fe, Zn or Ni in nanophase Ni- or Zn-ferrites may exhibit an absorbance feature for the 1s to 3d transition, which is forbidden by the selection rule in the case of perfect octahedral symmetry. The valency of hydrogenated ferrites was between 2 and 3. The EXAFS data showed that the nanophase Ni- or Zn-ferrites had two central Fe atoms coordinated by primarily Fe-O with bond distances of 1.87 Å. The bond lengths of Ni-O (Zn-O) in unhydrogenated and hydrogenated ferrites were 1.99 Å (1.87 Å) and 2.00 Å (1.88 Å), respectively. Recovery of valuable methane by decomposition of CO2 over Ni- or Zn-ferrite nanoparticles with recycling heat energy of offgas produced from power generation plant or steel industry is also an appealing resource recovery alternative in the future.

碩士
元智大學
化學工程與材料科學學系
95
Recent advance in technology has led to serious wasterwater pollution in Taiwan. As a result, many nitrate/nitrite wastewater treatment technologis has been evolved eventually. Therefore, the main objective of this research was to synthesize the nickel (Ni) or zinc (Zn) ferrites (Ni- or Zn-Fe2O4) and to reduce the concentration of nitrate/nitrite contaminants in wastewaters. The current research can be divided into four sections including synthesis of ferrites, application of ferrites on nitrate/nitrite contaminants removal, regeneration, and recycle or reuse of ferrite nanoparticles. Moreover, the kinetic parameters got by pseudo-first-order model equation were also found. Experimentally, nickel or zinc ferrite nanoparticles were synthesized under hydrothermal conditions (pH = 8.5, T = 453 K, and mixing rate of 1250 rpm) by precipitating from metal nitrates with aqueous ammonia. Synthesized nanopowders were characterized by X-ray powder diffractometer (XRPD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), BET surface area and porosimeter, electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared spectrometer (FTIR), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), ultraviolet-visible spectrophotometer (UV/Vis), and particle size meter. These results showed that the pore sizes of Ni, Zn-Fe2O4 were about 50-100 nm with spinal structure. Ni, Zn-Fe2O4 having strong characteristic peaks at 2θ = 35.66 and 35.24 were investigated by XRPD patterns, respectively. The specific surface area of Ni, Zn-Fe2O4 measured by ASAP isotherms were 100.4 and 170.7 m2/g, respectively. From ESCA spectra, the results showed that the Fe(2p) of Ni, Zn-Fe2O4 were at 711.05 and 711.25 eV respectively, Ni(2p) of NiFe2O4 were at 855.3 eV, Zn(2p) of ZnFe2O4 were at Zn(4) = 1021.95 eV, and Zn(6) = 1023.08 eV, respectively. By using FTIR spectra, the results showed that the characteristic peaks of Ni, Zn-Fe2O4 were about at 571 and 593 cm-1, respectively, the O-H characteristic peaks of Ni, Zn-Fe2O4 were at 1382 and 1380 cm-1, respectively. The XANES/EXAFS spectra showed that the valencies of the Ni, Zn-Fe2O4 were Ni(II) and Zn(II), respectively. The first shell of Fe-O bonding for Ni, Zn-Fe2O4 with bond distances were 1.95 and 1.94 Å and coordination numbers of 4.03 and 3.81, respectively before hydrogen reduction. Similarly, the first shell of Fe-O bonding for Ni, Zn-Fe2O4 with bond distances were 1.98 and 2.03 Å and coordination numbers of 4.03 and 3.81 respectively after hydrogen reduction at 573 K and 1 atm. The decomposition of nitrate or nitrite contaminants analyzed by UV/Vis was investigated by oxygen-deficient Ni, Zn-Fe2O4 formed by hydrogen reduction at 573 K and 1 atm. As indicated by the results from XRPD, TEM and FE-SEM, the fine structure of Ni, Zn-Fe2O4 did not change after the reaction. In terms of nitrate and nitrite wastewater treatment, the decomposition rates of Zn-ferrites were more efficient than the ones of Ni-ferrites at optimum operating condition at pH = 5 in room temperature. Reaction process described by pseudo-first-order model equation and the k value was increased while the wastewater concentration decreased. The optimized operating conditions were also applied on wasterwater treatment plants, it was found that Zn-ferrites were more efficient than the ones of Ni-ferrite nanoparticles. As shown by XRPD, TEM and FE-SEM analyses, the structure of Ni, Zn-Fe2O4 is very stable and can be recycled. The recyclibility rates of Ni, Zn-Fe2O4 were 98.25 and 98.36% repectively. Thus, the outcome of this study would be able to be applied on existing wasterwater treatment so as to improve the efficiencies of the processes.

abstract: The overall objective of this project is to optimize the development of magnetic ferrite thin films targeted for enabling low-loss broadband communication devices, miniaturized low-microwave inductors and electromagnetic noise suppressors. The focus of this objective is to design and build a reactor and improve the spin-spray process. Each film is then characterized and optimized to have a high permeability and high frequency in the range of 500 MHz - 3 GHz. Films produced by the µ-droplet deposition regime yields a higher Snoek's product than the continuous liquid layer regime. The highest Snoek's product occurs when it is deposited at an oxidant pH of 8.28. The Ni-Zn-Co ferrite magnetic domains were imaged using the Lorentz TEM in which multi-grain domains are experimentally observed for the first time.
Dissertation/Thesis
Ph.D. Materials Science and Engineering 2013

Im Rahmen dieser Arbeit wurde der Einfluss von Defekten auf die Eigenschaften von Ferrit-Dünnfilmen untersucht. Die Dünnfilme wurden mit Hilfe von gepulster Laserabscheidung bei verschiedenen Züchtungsparametern hergestellt. Durch Variation der Substrattemperatur und des Sauerstoffpartialdrucks wurden Dünnfilme verschiedener kristalliner Qualität gezüchtet. Diese wurden hinsichtlich ihrer chemischen Komposition mit Hilfe von energie-dispersiver Röntgenspektroskopie und Röntgenphotoelektronenspektroskopie untersucht. Durch Korrelation der Ergebnisse mit Messungen zum zirkularen magnetischen Röntgendichroismus, konnte eine partielle Inversion der Spinellstruktur nachgewiesen werden. Der Grad der Inversion ist höher für geringe Abscheidetemperaturen. Für diese defektreichen Dünnfilme zeigen Röntgenbeugungsuntersuchungen eine geringere kristalline Ordnung der Dünnfilme. Die strukturellen Defekte haben einen maßgeblichen Einfluss auf die elektrischen und magnetischen Eigenschaften der Ferrit-Dünnfilme. So zeigen die Ferrit-Dünnfilme für geringe Züchtungstemperaturen eine erhöhte elektrische Leitfähigkeit, während Dünnfilme, die bei hohen Substrattemperaturen gezüchtet wurden, isolierend sind. Die Temperaturabhängigkeit der elektrischen Leitfähigkeit kann auf thermisch aktivierte Hopping-Leitung oder die Leitung zwischen Clustern, die in einer Matrix eingebettet sind, zurückgeführt werden. Die magnetischen Eigenschaften von Zinkferrit-Dünnfilmen werden maßgeblich durch Defekte in der Spinellstruktur bestimmt, da es nominell in der normalen Spinellstruktur kristallisiert und daher antiferromagnetisch ist. Die partielle Inversion der Eisen- und Zinkionen führt zu Ferrimagnetismus in den Zinkferrit-Dünnfilmen, der mit Hilfe von SQUID-Messungen in dieser Arbeit eingehend untersucht wurde. Durch Korrelation der Ergebnisse der verschiedenen Untersuchungsmethoden konnten Rückschlüsse auf die dominierenden Defekte in den Ferrit-Dünnfilmen geschlossen werden. So sind zum einen Defekte auf atomarer Skala, wie Antisite-Defekte und divalenten Fe-Ionen für die erhöhte elektrische Leitfähigkeit und die größere Magnetisierung der defektreichen Dünnfilme verantwortlich. Zum anderen können ausgedehnte Defekte, im Speziellen Cluster, die in einer amorphen Matrix eingebettet sind, nicht ausgeschlossen werden.

碩士
東海大學
化學工程與材料工程學系
102
In this study, we reported on the surface micro-structure, surface roughness, electrical impedance, and forward transmission of manganese doped nickel-zinc-copper ferrites (Ni0.2Zn0.6Cu0.2Fe2O3 + x MnCO3). Ferrites were prepared by solid state and sol-gel methods and mixed with acrylic resin for spin and direct coatings onto plastic sheets. The surface roughness increases with the doping ratio of manganese, and also increases with the number of coating layers. Forward transmission of ferrite prepared by direct coating is lower than that of ferrite prepared by spin coating. The influence of the manganese doping ratio on forward transmission is not obvious. Electrical impedance of ferrite prepared by direct coating is higher than that of ferrite prepared by spin coating. The electrical impedance shift resulted by the manganese doping ratio of 0.3 is most closed to that resulted by the reference sample. The electrical impedance shift resulted by the manganese doping ratio of 0.7 is most different to that resulted by the reference sample. Ferrites prepared by solid state and sol-gel methods have no difference on forward transmission and electrical impedance. However, the result of changing sample size, sample thickness, and the amount of ferrite shows that the influence of thickness is most obvious on forward transmission, but they are not obvious on electrical impedance.

When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.