Internal magnetic fields in submicron particles of barium hexaferrite detected by 57Fe NMR |
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| Authors: | Helena ?těpánková Karel Kou?il Vojtěch Chlan Peter G?rnert Robert Müller Josef ?těpánek |
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| Institution: | 1. Charles University in Prague, Faculty of Mathematics and Physics, V Hole?ovi?kách 2, 180 00 Prague 8, Czech Republic;2. Innovent e.V. Technologieentwicklung, Prüssingstr. 27 B, D-07745 Jena, Germany;3. Institute of Photonic Technology, Albert-Einstein-Str. 9, D-07745 Jena, Germany;1. Department of Biology, Cell Biology Division, Gravitational Biology, Friedrich-Alexander-University Erlangen-Nuremberg, Germany;2. Faculty of Sciences, Friedrich-Alexander-University Erlangen- Nuremberg, Germany;3. Department of Botany, Kohat University of Science and Technology, 26000 Kohat, Pakistan;4. Department of Bioprocess Engineering, Friedrich-Alexander- University Erlangen-Nuremberg, Germany;1. Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina;2. Instituto de Física La Plata, CCT-La Plata, CONICET, Argentina;3. Universidad Nacional del Noroeste de la Provincia de Buenos Aires, Argentina;1. Department of Histology and Cell Biology, Faculty of Medicine, Mansoura University, Mansoura, Egypt;2. Department of Anatomy and Embryology, Faculty of Medicine, Mansoura University, Mansoura, Egypt;1. Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, Prague 120 00, Czech Republic;2. Institute of Inorganic Chemistry of the Czech Academy of Sciences, Husinec-Rez 1001, 250 68 Rez, Czech Republic;3. Department of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, V Holesovickach 2, 180 00 Prague, Czech Republic;4. Deutsches Elektronen Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany;5. Institute of Physics of the Czech Academy of Sciences, Cukrovarnicka 10, Prague 6 162 53, Czech Republic;1. Faculty of Mathematics and Physics, Charles University, V Hole?ovi?kách 2, 180 00 Prague, Czech Republic;2. Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 162 00 Prague, Czech Republic;3. First Faculty of Medicine, Charles University, Kate?inská 32, 121 08 Prague, Czech Republic;1. Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, Postfach 3640, 76021 Karlsruhe, Germany;2. Institute of Inorganic Chemistry, Ruprecht-Karls University Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany;3. Institute of Functional Interfaces, Karlsruhe Institute of Technology, Postfach 3640, 76021 Karlsruhe, Germany |
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| Abstract: | 57Fe nuclear magnetic resonance (NMR) spectra of hexaferrite BaFe12O19 powder samples prepared by glass crystallization method were measured at 4.2 K and analyzed in comparison to spectra of single crystals. Samples with various mean particle dimensions were tested. NMR spectral lines corresponding to individual iron sublattices showed pronounced frequency shifts of their positions and a significant line broadening compared to single crystals. The significant contribution to the line shifts and line shape had a uniform macroscopic origin giving identical absolute value of shifts and the same line shapes for all measured lines of a particular sample. Estimations of demagnetization fields based on mean particle dimensions reasonably corresponded to the observed frequency shifts for particle mean diameter 67 nm, or had a higher value for a sample with mean diameter of 340 nm, for which a presence of domain walls was detected by NMR. In the spectrum of a sample with the smallest particles (～16 nm), an additional contribution having broader lines and faster spin-spin relaxations was found. It could be assigned to weaker exchange interactions or deviations of magnetic moment directions from the hexagonal axis in a surface layer. |
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