Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-07-10T18:06:04Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação_Cecília.pdf: 3721060 bytes, checksum: cd2515bc852d6c7bb0fadaeef5673702 (MD5) / Made available in DSpace on 2017-07-10T18:06:04Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação_Cecília.pdf: 3721060 bytes, checksum: cd2515bc852d6c7bb0fadaeef5673702 (MD5) Previous issue date: 2016-01-22 / CNPQ / Este trabalho tem como objetivo analisar propriedades magnéticas de arranjos ordenados de nanofios de níquel depositados em membranas porosas de alumina. Um estudo sobre a preparação das amostras, relatando as etapas de formação da membrana e posterior eletrodeposição dos fios via corrente alternada, é feito inicialmente. Na sequência, características morfológicas e estruturais são observadas via microscopia eletrônica de varredura e mapas de energia dispersiva, de onde foi possível constatar que os fios possuíam diâmetros entre 30 nm e 40 nm e comprimentos entre 100 nm e 550 nm. As análises das propriedades magnéticas das amostras são baseadas nas curvas de histerese obtidas via magnetometria de amostra vibrante para diferentes direções de campo aplicado e de temperatura. O caráter de anisotropia magnética uniaxial que esses sistemas de nanofios possuem é observado através destas curvas, bem como o efeito que a interação dipolar entre os fios causa nas propriedades magnéticas do sistema. O laço de histerese nos fornece parâmetros magnéticos como coercividade e remanência e uma análise sobre seus comportamentos em função de parâmetros geométricos e morfológicos dos fios, direção de campo aplicado e temperatura são realizadas e comparadas com os resultados reportados na literatura. / This work aims to analyze magnetic properties of nickel nanowires arrays electrodeposited on porous anodic alumina membrane. A study of sample preparation is reported initially and then morphological and structural features are observed via scanning electron microscopy, from which we observe wires with diameters between 30 nm and 40 nm and lengths between 100 nm and 550 nm. The analysis of the magnetic properties are based on the hysteresis curves for different directions of applied field and temperature. The uniaxial magnetic anisotropy is observed as well the effect of the dipolar interaction between the wires. These curves also provides the magnetic parameters such as coercivity and remanence and we analyze their behavior as a function of geometric and morphological parameters, applied field direction and temperature, comparing with the results reported in the literature.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22114号 / 理博第4541号 / 新制||理||1652(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 若宮 淳志 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22272号 / 理博第4586号 / 新制||理||1658(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 大須賀 篤弘, 教授 依光 英樹, 教授 時任 宣博 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

PhD (Physics) / Department of Physics / Understanding how and why superconductivity (SC) occurs in a given material has been very challenging for physicists for more than a hundred years, notwithstanding the major milestones, such as the London theory, the Landau-Ginzburg theory, and the BCS theory. The extreme challenge to predict the occurrence of SC is symbolized by the long string of unanticipated but breathtaking advances, i.e., the unexpected discoveries of cuprates and Fe-pnictides being the dramatic modern examples. Because of their incompatibility, the nucleation of SC near a ferromagnet is di cult and has never been realized except for the case that another superconductor provides proximity-boosted Cooper pairs. This perceived necessity to start with another superconductor is engrained in the exten- sive study of the proximity e ect in superconductor/ferromagnet (S/F) powder sample, where all the structures involve a superconductor with either stable or metastable struc- ture. Compounding the di culty, it is also generally recognized that SC with substantial Tc is favourable in low dimensionality because of strong quantum uctuation. In this thesis, we report a serendipitous nding of SC that emerges under the most implausible circumstances in low eld microwave absorption measurement. This new revelation may lead to unconventional avenues to explore novel SC for applications in superconducting spintronics. By means of a varienty of techniques, including EPR, SEM, FTIR, PPMS/VSM and XRD, nanonickel incorporated YBCO in di erent weighting factors have been studied. With its complex chemical structure and magnetic properties, Ni-YBCO is far from well understood and the magentic behavior of the system under di erent conditions is investi- gated. From the dilute mixture of nanonickel particles, it is found that groups of normal Josephson junctions (JJs) and JJs due to YBCO-nickel-YBCO interparticle weaklinks form as nickel is ferromagnetic. We experimentally show, for the rst time multiple phase reversals in the non-resonant microwave absorption (NRMA) spectra from Ni-YBCO pos- sibly, due to the formation of JJs. We also show that these multiple phase reversals then vii depend on microwave power and temperature. We argue that microwave power induced coherence among some groups of JJs and breaking of some of the weaker JJs can then lead to the disappearance of multiple phase reversals at higher microwave power levels. Further, we also report a role of pair breaking e ects that shall give a linear eld de- pendence of the derivative microwave absorption signal, which is essentially the NRMA signal. This pair-breaking e ect dominates at temperatures closer to Tc as expected thermodynamically. The presence of two peaks in the system, results in high permeability ferromagnet which acts as a magnetic short circuit for magnetic ux density and creates low reluctance path. A transition from normal to anomalous does not occur in this work, because of the possibility of junction in the sample. As predictable at the region around the origin where the weaklinks are supposed to be very strong for a very low doping or low nanonickel addition ( 0.5 % wt), not much e ect was observed. However, when the nanonickel addition is increased to 2 % and 3% we see a signi cant change in the magnetization and the associated hysteresis, indicating ux pinning. / NRF

The main goal of the present work was the synthesis of alkaline-earth nitridomanganates (AExMnyNz) with extended anionic structures and the characterization of their electronic and magnetic properties. Up to now, only compounds with isolated nitridomanganate anions have been reported in the discussed ternary systems. A systematic exploratory synthesis, employing high-temperature treatment of AE nitrides and Mn under controlled N2 pressure, yielded more than ten new nitridomanganates. Their crystal structures contain anionic building blocks of different dimensionalities, ranging from isolated species to three-dimensional frameworks. In general, the formation of Mn-rich compositions was found to be driven by the emergence of Mn-Mn interactions, which creates a link between nitridometalates and transition-metal-rich binary nitrides. The obtained nitridomanganates display a plethora of interesting phenomena, such as large spin-orbit coupling, magnetic frustration, quenching of magnetism due to Mn-Mn interactions, and metal-insulator transition.

This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.

In diesem Beitrag wird der Neuaufbau eines Versuchsstandes beschrieben, der zur Untersuchung magnetischer Eigenschaften von ferromagnetischen Werkstoffen dient. Angefangen bei der Notwendigkeit eines solchen Versuchsstandes werden der Aufbau, die Komponenten sowie die Besonderheiten beschrieben und erste Messergebnisse nach der Inbetriebnahme gezeigt. / This paper describes the new construction of a test bench used to investigate magnetic properties of ferromagnetic materials. Starting with the necessity of a test bench of this kind, the setup, the components and the special features are described and the first measurement results are shown after commissioning.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18234号 / 工博第3826号 / 新制||工||1586(附属図書館) / 31092 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 北川 進, 教授 松田 建児, 教授 濵地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20182号 / 理博第4267号 / 新制||理||1613(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 嶺重 慎, 准教授 前田 啓一, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The magnetic properties of NiMnGe1−xAlx, Ni50Mn35(In1−xBx)15, Ni50Mn35In14.5B0.5 (Bulk, As-Solidified and Annealed melt-spun ribbon) and RE-Infuse Carbon Nanotubes, have been studied by x-ray diffraction, differential scanning calorimetry (DSC), and magnetization measurements. Partial substitution of Al for Ge in NiMnGe1−xAlx results in a first-order magnetostructural transition (MST) from a hexagonal ferromagnetic to an orthorhombic antiferromagnetic phase at 186 K (for x = 0.09). A large magnetic entropy change of ∆SM = -17.6 J/kg K for ∆H = 5 T was observed in the vicinity of TM = 186 K for x = 0.09. This value is comparable to those of well-known giant magnetocaloric materials, such as Gd5Si2Ge2, MnFeP0.45As0.55, and Ni50Mn37Sn13. The values of the latent heat (L = 6.6 J/g) and corresponding total entropy changes (∆ST = 35 J/kg K) have been evaluated for the MST using DSC measurements. Large negative values of ∆SM of -5.8 and -4.8 J/kg K for ∆H = 5 T and up to 9T in the vicinity of TC were observed for x = 0.09 and 0.085, respectively. The impact of B substitution in Ni50Mn35In15-xBx Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5-400 K ). Direct adiabatic temperature change (ΔTAD) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔTAD = 2.5 K was observed at the magnetostructural transition for Ni50Mn35In14.5B0.5. The structural phase transition temperatures, phase structure, and parameters of the magnetocaloric effect (MCE) of Ni50Mn35In14.5B0.5 as Bulk, As-Solidified and Annealed melt-spun ribbon has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (oH) up to 5 T, and in the temperature interval 5–400 K). Magnetic and structural transitions in Ni50Mn35In14.5B0.5 as ribbons were found to coincide in Ni50Mn35In14.5B0.5 bulk sample, leading to a large magnetocaloric effects associated with the first-order magnetostructural phase transition. In comparison to the bulk Ni50Mn35In14.5B0.5 alloys, both the martensitic transition temperature (TM) and Curie temperature (TC) shifted to lower temperatures. Magnetic measurements revealed that the ribbons undergo a structure transformation similar to the bulk material at the martensitic transformation. The temperature of the transformation depends strongly on lattice parameters of the ribbons. MST shows a weak broad magnetic transition at TCM∼ 160 K, while the Curie temperature of AST TCA is ∼ 297 K. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni50Mn34.8In14.2B and Ni50Mn35In14X (X = In, Al, and Ge) Heusler alloys. These results suggest the possibility to control the martensitic transition in Ni50Mn35In14.5B0.5 through rapid solidification process. A comparison of magnetic properties and magnetocaloric effects in Ni50Mn35In14.5B0.5 alloys as Bulk, As-Solidified and Annealed ribbons is discussed. Carbon nanotube (CNT)/metal-cluster-based composites are envisioned as new materials that possess unique electronic properties which may be utilized in a variety of future applications. Super paramagnetic behavior was reported for CNTs with Gd ions introduced into the CNT openings by internal loading with an aqueous GdCl3 chemical process. In the current work, the magnetic properties of the CNT/Gd composites were obtained by the joining and annealing of Gd metal and CNTs at 850 °C for 48 h. Energy dispersive X-ray analysis shows the presence of Gd intermingled with the CNT walls with maximum and average Gd concentrations of about 20% and 4% (by weight), respectively. The Gd clusters have a non-uniform distribution and are mostly concentrated at the ends of the CNTs. A ferromagnetic-type transition at TC ∼ 320 K, accompanied by jump like change in magnetization and temperature hysteresis typical for the temperature induced first order phase transitions has been observed by magnetization measurements. It was found that Gd infused into the CNTs by the annealing results in a first order paramagnetic-ferromagnetic transition at TC = 320 K.