Numerous techniques are used to study the magnetic history and properties of rocks, which provides important data on the Earth’s interior. In this study we conducted a series of experiments on two different sample sets, comprising pure magnetite (Set1) and a mixture of magnetite-hemoilmenite-bearing quartzite (Set2), in order to gather information about their magnetic susceptibility and remanent magnetization. A miniature diamond anvil cell (mDAC) constructed from hardened non-magnetic alloy (40HNU) was used for high pressure experiments. With the help of high sensitivity susceptibility bridge (MFK1-FA Kappabridge, AGICO), we measured the susceptibility of three samples and of the mDAC. Consequently, we loaded one of the samples in the mDAC and acquired susceptibility measurements during the compression and decompression of the system. For remanence measurements we used a 2G Enterprises SQUID magnetometer. We measured the natural remanent magnetization (NRM) and performed alternating field (AF) demagnetization on ten samples and on the mDAC. Additionally, isothermal and anhysteretic remanent magnetization (IRM and ARM) acquisition were performed on nine and one samples, respectively and demagnetization on three and one samples, respectively. Results showed that Set1 samples consist of both SD and MD magnetite grains. Regarding Set2 samples, the main magnetic carriers are SD and MD magnetite or titanium bearing magnetite grains, while there are indications that hematite and ferrimagnetic titanohematite might be present as well. The presence of eddy currents, due to the conducting materials of the mDAC, resulted in masking the signal of the sample making it difficult to draw any safe conclusions regarding how the susceptibility of the sample changes with pressure. All in all, there was a satisfactory response of the instruments working with very small amounts of material and an adequate signal stability of both the samples and the mDAC. Our study provided us with an insight into high pressure experiments and showed possible directions for future studies. / Många metoder används för att studera magnetiska egenskaper i berg, vilket ger viktig information om Jordens inre. I denna studie genomförde vi en rad experiment på två olika uppsättningar prov, innefattande ren magnetit (Set1) och en blandning av magnetit-hemoilmenit-bärande kvartsit (Set2), för att samla information om deras magnetisk susceptibilitet och magnetiska remanens. En miniatyr diamantstädcell (mDAC) konstruerad av en härdad icke-magnetisk legering (40HNU) användes för högtrycksexperiment. Susceptibilitetet av tre prover och av mDAC mättes en MFK1-FA Kappabridge, AGICO. Följaktligen monterade vi ett av proverna i mDAC och vi genomförde susceptibilitetsmätningar under kompression och dekompression. Vi använde en 2G Enterprises SQUID magnetometer för remanensmätningar. Den naturlig remanentmagnetiseringen (NRM) mättes och vi utförde alternerande fält (AF) demagnetisering på tio prover och på mDAC. Dessutom genomfördes isotermisk och anhysteretisk remanentmagnetisering (IRM och ARM) på nio respektive ett prover, och demagnetisering på tre respektive ett prover. Resultaten visade att Set1-prover består av både enkeldomän (SD) och multidomän (MD) magnetit. SD och MD magnetit- och titanomagnetitkorn är de viktigaste magnetiska mineral av Set2-prover, medan finns det indikationer på att hematit och ferrimagnetisk titanohematit också bidrar till signal. Virvelströmmar, som skapats av mDACs ledande material, maskerade provets magnetiska susceptibilitet och det var svårt att kommentera på hur provets susceptibilitet förändras med tryck. Sammantaget var instrumentens prestanda tillfredsställande, även vid små mängder material. Prov och mDACs signalstabilitet var också adekvat. Vår studie gav oss en inblick i högtrycksexperiment och magnetiska egenskaper och den visade möjliga riktningar för framtida studier.

The COSC-1 borehole located in the Lower Seve nappe of the Central Scandinavian Caledonides is intended to study the tectonic evolution of the Paleozoic orogen. The drilling project reached a depth of 2495.8m and obtained samples from different lithologal units of mica schist, amphibolite, gneiss, and mylonitic gneisses.     To test if the samples are suitable for paleomagnetism, laboratory measurements of natural remanent magnetism are performed on sub-samples of the COSC-1 drill core in the paleomagnetic laboratory with alternating field demagnetization, IRM acquisition as well as the temperature dependence of susceptibility measurements. Important properties of the samples such as coercivity, Curie temperature, inclination, and declination are determined with the measurements.     Most of the samples carry a remanent magnetization that can be readily demagnetized with alternating field demagnetization up to 100 mT. Some of the samples may be suitable for paleomagnetism, with the major ferromagnetic mineral compositions of magnetite, hematite, and FeTi oxides. However, low coercivities and median destructive fields suggest that the magnetite-bearing samples will be prone to remagnetization, making them more challenging to use in terms of retrieving a primary magnetization originating from the Caledonian orogeny. The thermomagnetic results of some samples reflect the metamorphic conditions experienced by the rocks and the mineral assemblage changed irreversibly during step-wise heating experiments. These results can possibly be used as an indicator for the metamorphic temperature experienced by the different lithologal units. Although further measurements are needed to get a clearer understanding of the suitability of the COSC-1 sample for paleomagnetic reconstructions (including thermal demagnetization experiments), this thesis indicates that the COSC-1 rocks contain interesting paleo- and rock magnetic features that are worth further study.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20564号 / 医博第4249号 / 新制||医||1022(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 増永 慎一郎, 教授 妹尾 浩, 教授 鈴木 実 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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В работе изучается динамическая восприимчивость феррожидкости, которая моделируется системой взаимодействующих подвижных магнитных частиц. Предполагается, что система находится в постоянном и переменном магнитном полях, направленных параллельно друг другу. / In this work, we study the dynamic susceptibility of a ferrofluid, which is modeled by an system of interacting moving magnetic particles. It is assumed that the system is in a constant and an alternating magnetic field, directed parallel to each other.

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Ever since the discovery of the giant magnetocaloric effect (GMCE) in the Gd5(Si,Ge)4 phases, magnetic cooling has gained significant interest because of its potential environmental benefits and increased efficiency compared to vapour-based refrigeration. This current work is focused on one of the most promising GMCE systems, the (Mn,Fe)2(Si,P) materials. An alternative synthetic route has been explored for the Mn2-xFexSi0.5P0.5 and MnFeSiyP1-y series which is capable of producing phase-pure samples. The new preparation technique eliminates common impurities that arise from established methods thus providing a more accurate description of the structural and physical properties. The low cost, non-toxicity, abundance of starting materials and easy tuning of the magnetic properties make these materials desirable for potential applications. Phase-pure magnetocaloric Mn2-xFexSi0.5P0.5 materials (x = 0.6, 0.7, 0.8, 0.9) were synthesized through arc-melting followed by high temperature sintering. Structural features of samples with x = 0.6, 0.9 were studied through temperature dependent synchrotron powder x-ray diffraction. Magnetic measurements established the Curie temperature, thermal hysteresis, and magnetic entropy change of this system. According to the diffraction and magnetization data, all of the samples were shown to have a first-order magnetostructural transition which becomes less pronounced for Mn-richer samples. The MnFeSixP1-x phases (x = 0.30, 0.35, 0.40, 0.48, 0.52, 0.54, 0.56) have also been synthesized by the same method. For the first time, single crystals of x = 0.30, 0.40 were successfully grown. Variable temperature x-ray diffraction experiments for x = 0.30 were completed which show the structural changes across the phase transition. This structural data was complemented with magnetization data providing Curie temperatures and thermal hysteresis. / Thesis / Master of Science (MSc)