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You searched for subject:(Verwey). Showing records 1 – 3 of 3 total matches.

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1. Bjork, Andreas. Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget.

Degree: Geophysics, 2018, Uppsala University

Laboratory magnetic measurements are used to develop a methodology to characterize the Kiruna-type Rare Earth Elements (REE) bearing apatite iron-oxide deposits at Blötberget in central Sweden. This high-grade ore deposit is known to have sharp boundaries between lens shaped main ore bodies of magnetite-rich ore, and a complex hematite-rich ore associated with pegmatites and skarn formation. The thesis covers laboratory magnetic measurements of 37 samples originating from eight drill cores and reference samples from previously mined area. It focuses on on-covering how the samples relate in terms of magnetic susceptibility, further its dependency on temperature, frequency, field and the orientation. The results are correlated with petrographic analysis previously performed on accompanying thin sections. The measurements show that magnetite with strong susceptibility contribution overshadow the hematite contribution in the samples. Transition changes in susceptibility are noticeable when crossing the Verwey temperature; -153°C, Curie temperature; 580°C and Néel temperature; 680°C. The Morin temperature appears at -60°C, or is missing. Linear relationships are identified between the magnitude difference in susceptibilities across transitions at high temperature and wt% magnetite and hematite have been identified. The Blötberget skarn and hematite-rich ore samples have a higher degree of susceptibility anisotropy than the other ore-types. Blötberget samples are dominated by multidomain characteristics in remanence, saturation and coercivity. High temperature measurements have shown that the magnetite is close to pure. The low temperature measurements suggest hematite is impure or bears a petrological footprint. The study also shows that rich iron ore samples sometimes can be at risk of being overlooked with standard methods of measuring susceptibility

Laboratorietekniska metoder kan användas som ett komplement till malmgeologi och geofysisk prospektering. I denna metodstudie karaktäriseras apatitjärnmalm från Blötberget, nära Grängesberg. En fyndighet bestående av linsformade malmkroppar rika på magnetit och ofta avskilda men komplexa hematitrika stråk. Studien är gjord 37 prover från totalt 8 borrkärnor, och lokaler som tillhörde produktion från gruvverksamhet under 1900-talet. Mätmetoderna fokuserar på att kartlägga malmens magnetiska egenskaper, och hur temperatur, frekvens, fältstyrka samt riktning påverkar dessa. Resultaten jämfördes med tidigare petrografisk studie av tillhörande tunnslip Resultaten visar att magnetit står för merparten av susceptibiliteten i proverna, men att även hematit kan urskiljas och kvantifieras. Temperaturberoende har påvisats vid övergångar för Verwey-temperatur; -153°C, Curie-temperatur; 580 °C, och Néeltemperatur; 680 °C. Den förväntade Morin-temperaturen vid -14°C, påträffades vid -60 °C eller saknas helt för flera av de hematitrika proverna. Magnetiskt anisotropa prover återfinns bland prover som identifierats som skarn eller hematitrika. Magnetisk…

Subjects/Keywords: Verwey; Morin; Curie; Néel; magnetite; hematite; alteration; iron-ore; quality control; kappabridge; hysteresis; susceptibility; anisotropy; Verwey; Morin; Curie; Néel; magnetit; hematit; oxidation; järnmalm; kvalitetskontroll; kappabridge; hysteresis; susceptibilitet; anisotropi; Geophysics; Geofysik

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APA (6th Edition):

Bjork, A. (2018). Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget. (Thesis). Uppsala University. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-347975

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Bjork, Andreas. “Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget.” 2018. Thesis, Uppsala University. Accessed March 05, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-347975.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Bjork, Andreas. “Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget.” 2018. Web. 05 Mar 2021.

Vancouver:

Bjork A. Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget. [Internet] [Thesis]. Uppsala University; 2018. [cited 2021 Mar 05]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-347975.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Bjork A. Characterizing magnetic susceptibility and remanent magnetization of magnetite and hematite rich drill-core samples at Blötberget. [Thesis]. Uppsala University; 2018. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-347975

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University of New South Wales

2. Chang, Fenfen. Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.

Degree: Physics, 2017, University of New South Wales

Multiferroics exhibit tremendous potential in technological applications, of which the interplaybetween the ferro-/antiferromagnetic, ferroelectricity, and ferroelasticity can be manipulatedby external parameters such as electric or magnetic fields and even can be created byproper control of internal parameters, such as oxygen-content, cation doping, and internalpressure. Invaluable insight into the multiferroicity can be provided by investigating the roleof such parameters in the crystallographic and magnetic structures of transition metal oxides.In this thesis, a comprehensive studies of contribution of oxygen-deficiencies and cation dopingto the various phases are presented, which utilize the neutron and synchrotron powderdiffraction.The multivalent nature of cobalt ions in SrCoO3􀀀d causes an oxygen-content dependentphase diagram. It is vital to determine the precise crystallographic and magnetic structure ofoxygen-vacancy ordered SrCoO3􀀀d , which provides prerequisite to reveal the mechanism ofits multiferroicity in the corresponding thin film samples. Using the neutron and synchrotronpowder diffraction techniques, the correct space group and precise magnetic structures aredetermined for the different oxygen-vacancy ordered phases: the brownmillerite SrCoO2:5,the tetragonal SrCoO2:875, and the cubic SrCoO3.Ferroelectricity can be induced by the canted spin configuration, which exists widely inthe frustrated spin systems. With such an expectation, Zn-substituted CuFe2O4 was studiedand a comprehensive phase diagram was built for Cu1􀀀xZnxFe2O4. Spin canting couldlead to a spin spiral phase which could possibly induce a multiferroic state as observed inCuFeO2. The purpose of this project was to further investigate the spin canting in ZndopedCuFe2O4 and elucidate the possibility of multiferroicity in this system. Furthermore,pure ZnFe2O4 is already an interesting highly frustrated spin system. Magnetite is the oldestknown magnet. As the first known multiferroics, the ferroelectricity in Fe3O4 is drivenby the Verwey transition. However, the microscopic origin of the Verwey transition in Fe3O4is still in debate. In order to obtain a deeper insight into the mechanism of the charge ordering,Cu-doped Fe3O4 was investigated using the high-resolution neutron and synchrotrondiffraction. The main emphasis was the stability of the Verwey transition with charge carrierdoping. Advisors/Committee Members: Ulrich, Clemens, Physics, Faculty of Science, UNSW, Sushkov, Oleg, Physics, Faculty of Science, UNSW.

Subjects/Keywords: Oxygen vacancy ordering; Neutron diffraction; Synchrotron powder diffraction; Verwey transition; Charge ordering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Chang, F. (2017). Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true

Chicago Manual of Style (16th Edition):

Chang, Fenfen. “Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.” 2017. Doctoral Dissertation, University of New South Wales. Accessed March 05, 2021. http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true.

MLA Handbook (7th Edition):

Chang, Fenfen. “Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels.” 2017. Web. 05 Mar 2021.

Vancouver:

Chang F. Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. [Internet] [Doctoral dissertation]. University of New South Wales; 2017. [cited 2021 Mar 05]. Available from: http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true.

Council of Science Editors:

Chang F. Search for novel multifunctional materials: a comprehensive neutron and synchrotron diffraction study on cobaltates and spinels. [Doctoral Dissertation]. University of New South Wales; 2017. Available from: http://handle.unsw.edu.au/1959.4/57563 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:43656/SOURCE02?view=true


University of Minnesota

3. Lindquist, Anna K. Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects.

Degree: PhD, Geophysics, 2013, University of Minnesota

Magnetite (Fe3O4) is the most important mineral to the rock magnetic and paleomagnetic communities and is ubiquitous in igneous, sedimentary, and metamorphic rocks. Larger multidomain (MD) magnetite grains are more common than single domain grains, so understanding how they record paleomagnetic fields would be a boon to paleomagnetists. MD magnetite grains are divided into multiple domains, regions with uniform magnetization, separated by domain walls. Domain walls sweep through magnetite grains easily, so slight changes in ambient magnetic fields can alter the magnetization of MD magnetite. Because of this, MD magnetite is not considered reliable for paleomagnetic studies, and the mechanisms by which MD grains may record past magnetic fields are not well understood. Dislocations, linear crystallographic defects, may increase magnetic coercivity by pinning domain walls in place. This study, for the first time, experimentally investigates this pinning behavior by using a transmission electron microscope (TEM) to simultaneously image magnetic domain walls, dislocations, and low-temperature twin structures. Magnetite grains were deformed in the dislocation glide regime, which is active in natural magnetite grains. Dislocations were not uniformly distributed throughout the sample, but regions with more and longer dislocations pinned domain walls more strongly. First-order reversal curve diagrams demonstrate the presence of regions with pinning strengths of over 125 mT. The strength of domain wall pinning at dislocations was found experimentally and theoretically to be proportional to dislocation length, with longer dislocations pinning more strongly. Average pinning fields were around 0.2 mT. Magnetite grains with more uniformly distributed dislocations would likely have coercivities that were high enough to enable MD magnetite to record geomagnetic fields over geologic timescales. Further, low-temperature TEM and magnetic studies demonstrated that dislocations can affect twin growth in magnetite below the Verwey transition. Deformed magnetite samples had more soft-shouldered Verwey transitions and were able to retain more remanence after low-temperature demagnetization (LTD). Therefore, MD magnetite grains may be able to retain relevant magnetizations, even after LTD. Dislocation length, density, and distribution are then all important considerations when investigating the ways in which MD magnetite may retain a stable record of paleomagnetic field characteristics, even after LTD.

Subjects/Keywords: Geophysics; Dislocation; Domain wall; Magnetite; Multidomain; Transmission electron microscopy; Verwey

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lindquist, A. K. (2013). Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects. (Doctoral Dissertation). University of Minnesota. Retrieved from http://purl.umn.edu/159854

Chicago Manual of Style (16th Edition):

Lindquist, Anna K. “Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects.” 2013. Doctoral Dissertation, University of Minnesota. Accessed March 05, 2021. http://purl.umn.edu/159854.

MLA Handbook (7th Edition):

Lindquist, Anna K. “Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects.” 2013. Web. 05 Mar 2021.

Vancouver:

Lindquist AK. Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects. [Internet] [Doctoral dissertation]. University of Minnesota; 2013. [cited 2021 Mar 05]. Available from: http://purl.umn.edu/159854.

Council of Science Editors:

Lindquist AK. Dislocations in Magnetite: Experimental Observations of their Structural, Magnetic, and Low-temperature Effects. [Doctoral Dissertation]. University of Minnesota; 2013. Available from: http://purl.umn.edu/159854

.