Microscopy and rock magnetism of fine grain-size titanomagnetite from the Jacupiranga Alkaline Complex,Brazil: unearthing Ti-magnesioferrite nanoparticles |
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Authors: | Luis M Alva-Valdivia María de la Luz Rivas-Sánchez Jesús Arenas-Alatorre Avto Goguitchaishvili Omar Ferreira Lopes |
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Institution: | Laboratorio de Paleomagnetismo, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México DF, México;Departamento de Materia Condensada, Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México DF, México;Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofísica, Universidad Nacional Autónoma de México, Campus Morelia, Michoacán, México;Universidade Federal do Paraná, Departamento de Geología, Jardim das Américas, Curitiba, Paraná, Brazil |
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Abstract: | Very fine samples from the mineralized zones of the Jacupiranga complex at the Cajati mine were selected for crystallographic identification of Ti-magnesioferrite (TMf) nanostructures embedded in titanomagnetite (TM) using high-resolution transmission electron microscopy (TEM). A magnetic concentrate obtained of pyroxenite samples (sites 4 to 7) was reduced and divided into fractions of distinct range sizes: 26±2 μm, 19±1 μm, 13±1 μm, 9±1 μm, 6±1 μm and 6-0.1 μm. The mineralized samples of carbonatite and pyroxenite were characterized by X-ray diffraction, transmitted and reflected light microscope, and scanning electron microscope with multielemental analysis. The finest magnetic concentrate sample (MC6) was analyzed under high-resolution transmitted electron microscopy (TEM) and high angle annular dark field and Raman spectroscopy. Magnetic properties were measured for the distinct granulometric fractions, showing drastic changes when grain sizes go beyond the frontier from micro to nanometer sizes. Frequency-dependent magnetic susceptibility percentage (÷fd%) report higher values (10.2%) for the finer fractions (6±1 μm and 6-0.1 μm) attributed to dominant fractions of superparamagnetic particles. Nanometer and < 6 μm grain size TMf in TM particles require a magnetic field up to 249 mT to reach saturation during the isothermal remanent magnetization experiment. Coercivity and remanent magnetization of these samples increase when the particle size decreases, probably due to parallel coupling effects. Magnetic susceptibility versus temperature experiments were conducted two times on the same (< 35 nm) sample, showing that the repetition during the second heating is probably due to the formation of new TMf nanoparticles and growth of those already present during the first heating process. |
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Keywords: | nanopartículas de titanomagnesio-ferrita propiedades magnéticas mineralogía efecto del tamaño de grano complejo alcalino Jacupiranga Brasil TMf nanoparticles magnetic properties mineralogy grain size effect Jacupiranga Alkaline Complex Brazil |
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