Exploring the direct synthesis of exchange-spring nanocomposites by reduction of CoFe2O4 spinel nanoparticles using in situ neutron diffraction
| Autor: | Frederik Holm Gjørup, Henrik L. Andersen, Mogens Christensen, Jakob Voldum Ahlburg, Cecilia Granados-Miralles |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Nanocomposite
Materials science Magnetic domain Spinel Neutron diffraction Analytical chemistry 02 engineering and technology Coercivity engineering.material 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Magnetization Remanence engineering General Materials Science 0210 nano-technology Saturation (magnetic) |
| Zdroj: | Ahlburg, J V, Granados-Miralles, C, Gjørup, F H, Andersen, H L & Christensen, M 2020, ' Exploring the direct synthesis of exchange-spring nanocomposites by reduction of CoFe 2 O 4 spinel nanoparticles using in situ neutron diffraction ', Nanoscale, vol. 12, no. 17, pp. 9440-9451 . https://doi.org/10.1039/d0nr00912a |
| DOI: | 10.1039/d0nr00912a |
| Popis: | In situ neutron powder diffraction (NPD) was employed for investigating gram-scale reduction of hard magnetic CoFe2O4 (spinel) nanoparticles into CoFe2O4/CoFe2 exchange-spring nanocomposites via H2 partial reduction. Time-resolved structural information was extracted from Rietveld refinements of the NPD data, revealing significant changes in the reduction kinetics based on the applied temperature and H2 available. The nanocomposite formation was found to take place via the following two-step reduction process: CoxFe3-xO4 → CoyFe1-yO → CozFe2-z. The refined lattice parameters and site occupation fractions indicate that the reduced phases, i.e. CoyFe1-yO and CozFe2-z, initially form as Co-rich compounds (i.e. y > 0.33 and z > 1), which gradually incorporate more Fe as the reduction proceeds. The reduction depletes the Co-content in the parent spinel, which may end up becoming magnetically soft Fe3O4 at high temperature (T = 542 °C), while at lower temperatures there may be a co-existence of Fe3O4 and γ-Fe2O3 or CoxFe3-xO4. The macroscopic magnetic properties of the products were measured by vibrating sample magnetometry (VSM) and revealed the hard and soft magnetic domains in the nanocomposites to be effectively exchange-coupled. An increase of approximately 70% in specific saturation magnetisation, remanence magnetisation, and coercivity compared to the parent CoFe2O4 material was achieved for the best sample. |
| Databáze: | OpenAIRE |
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