Thesis (Ph.D.)--University of Western Australia, 2004.

PURPOSE: To assess the variability of incidental magnetization transfer effect (MT) by the number of slices and the magnetic field strength. METHODS: Various magnetic resonance images (MRI) were obtained with a phantom containing a series of solutions of gadolinium (Gd) and sucrose in distilled water, agarose gel and two vials with olive oil and distilled water. A diffusion weighted image (DWI) sequence was acquired to determine diffusion coefficient for each component of the phantom. Several inversion recovery (IR) sequences having different TI values were run for single-slice and used to calculate T1 relaxation time with maximum precision and minimizing magnetization transfer effect. The T1 relaxation value resulting from processing IR sequences was used as reference value. The mixed-TSE sequences were used to calculate T1, T2 and PD values and to assess MT effect for single-slice as for multi-slice acquisition. All the DICOM MR images were processed using various algorithms programmed in Mathcad (version 2001i, PTC Needham, MA) by Dr. Hernan Jara. According with the potential of each sequences the programs generated the qMRI maps and values of T1, T2, PD were obtained for all the components of the phantom. Values resulted from Mathcad calculation were used for analysis. All the acquisitions, calculations and measurements were performed for 1.5T and 3T field strength.

In this thesis the result x-ray diffraction, magnetic susceptibility, magnetization, and Mössbauer spectroscopy measurements of EuPdGe3, Al13Fe4, and FeNiSn are reported. The compound EuPdGe3 crystallizes in the BaNiSn3-type tetragonal structure (space group I4mm) with the lattice constants a = 4.4457(1) Å and c = 10.1703(2) Å. The results are consistent with EuPdGe3 being an antiferromagnet with the Néel temperature TN = 12.16(1) K and with the Eu spins S = 7/2 in the ab plane. The temperature dependence of the magnetic susceptibility above TN follows the modified Curie-Weiss law with the effective magnetic moment of 7.82(1) 𝜇𝐵 per Eu atom and the paramagnetic Curie temperature of −5.3(1) K indicative of dominant antiferromagnetic interactions. The M(H) isotherms for temperatures approaching TN from above are indicative of dynamical short-range antiferromagnetic ordering in the sample. The temperature dependence of the hyperfine magnetic field follows a S = 7/2 Brillouin function. The principal component of the electric field gradient tensor is shown to increase with decreasing temperature and is well described by a 𝑇32⁄ power-law relation. The Debye temperature of EuPdGe3 determined from the Mössbauer data is 199(2) K. The compound Al13Fe4 crystallizes in the monoclinic space group C2/m, in which Fe atoms are located at five inequivalent crystallographic sites, with the lattice parameters a = 15.503(2) Å, b = 8.063(2) Å, c = 12.464(2) Å, and β = 107.71(2)°. It is demonstrated that zero-field Mössbauer spectra can be decomposed into three quadrupole doublets. With the aid of the calculated electric field gradient (EFG) parameters we show that the first doublet results from one Fe site, the second doublet is due to two other Fe sites, and the third doublet originates from the last two Fe sites. We find that the shape of the Mössbauer spectrum of Al13Fe4 measured in an external magnetic field of 90 kOe can be accounted for with five component subspectra generated using the calculated II EFG parameters at five inequivalent Fe sites. The quadrupole splittings corresponding to three component doublets are shown to increase with decreasing temperature and are well described by a 𝑇32⁄ power-law relation. The Debye temperature of Al13Fe4 is found to be 383(3) K. We find a pseudogap in the density of states (DOS), with a width of ∼ 0.2 eV, that is centered 0.1 eV above the Fermi energy. The finite DOS at the Fermi energy confirms good metallicity of Al13Fe4. The 1/T-like dependence of the magnetic susceptibility shows that Al13Fe4 is a paramagnet. The compound FeNiSn crystallizes in the ZrBeSi-type crystal structure (space group P63/mmc) with the lattice constants a = 4.1329(1) Å and c = 5.1912(2) Å. It is a ferromagnet with the Curie temperature TC = 1024(10) K. Evidence is provided for a possible phase separation in the studied compound, into a majority magnetic phase and a minority, nanoscale, disordered phase with the corresponding iron magnetic moments at 4.6 K of 2.39(1) and 1.17(1) 𝜇𝐵. It is demonstrated that FeNiSn decomposes at a temperature significantly below TC when it is annealed in vacuum for about 30 hours. The Debye temperature of FeNiSn is found to be 445(6) K.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24482号 / 医博第4924号 / 新制||医||1063(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 岩田 想, 教授 萩原 正敏, 教授 椛島 健治 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Flux trapping and cycling energy losses were studied by vibrating sample magnetometry in fine multifilamentary Nb-Ti superconductive strands for which proximity effect coupling between the filaments is significant. Measurements were made to determine the influence of helical twist about the strand axis as well as sample length for strands experiencing varying levels of proximity effect coupling. The proximity effect strength was varied by investigating strands with a range of filament diameters, as well as by the addition of magnetic impurities to the interfilamentary medium (the matrix) to suppress the proximity effect. Critical currents and fields for the matrix were extracted from the measurements. The reduction of cycling loss1 and magnetization2 previously found was confirmed. Additionally, these measurements were extended to strands where little twist was applied, and the magnetization and cyclic loss were found to saturate. Bean-like models for anisotropic media introduced by Carr1 and later Harada2 were further developed to calculate magnetization and penetration fields in these strands over a large range of twist pitch values. A calculation of magnetic hysteresis loops was also made for short strand samples. These models provide a good qualitative understanding of the observed behavior and lead to useful predictions for applications. / Department of Energy

No description available.

The magnetization damping properties of square permalloy elements were characterized. These 20 nm-thick permalloy squares were deposited by the electron beam evaporation. Time resolved magneto-optic Kerr effect microscopy (TR-MOKE) was used to measure the magnetization evolution in the sample. By curve fitting in Matlab, I obtained the value of damping constant that is consistent with the reference paper. A Landau confi guration in the square permalloy sample leads to the different trends of the damping constant with external bias field. The damping constant in the bottom domain is found to decrease with increasing bias field while the damping constant in the top domain has been saturated into the minimum value. The decreasing tendency of magnetization precession frequencies is consistent with the Kittel equation modi fied with an anisotropic energy term. Additionally, FePt thin films and patterned CoFeB disks were investigated but neither yielded conclusive dynamic data. / Graduate / 0611 / 0607 / 0752 / leizhang.summer@gmail.com

No description available.

Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2008. / Title from PDF t.p. (viewed on July 23, 2009) Includes bibliographical references (p. 50-52). Also issued in print.

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