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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Magnetic fluctuations in nanosized goethite (α-FeOOH) grains
D E Madsen1, L Cervera-Gontard, T Kasama
1Department of Physics, Building 307, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
Summary
Defects in antiferromagnetic goethite (α-FeOOH) nanoparticles cause weakened magnetic coupling. This explains observed Mössbauer spectral broadening, suggesting defects impact other nanograin magnetic systems.
Area of Science:
- Materials Science
- Solid State Physics
- Nanotechnology
Background:
- Antiferromagnetic goethite (α-FeOOH) nanoparticles exhibit unusual Mössbauer spectra with temperature-dependent asymmetric line broadening.
- This broadening is unexpected given the large magnetic anisotropy, which should minimize magnetic relaxation effects.
Purpose of the Study:
- To investigate the cause of asymmetric line broadening in Mössbauer spectra of goethite nanoparticles.
- To understand the role of structural defects in the magnetic properties of antiferromagnetic nanograins.
Main Methods:
- High-resolution transmission electron microscopy (HRTEM) was used to examine goethite particle microstructure.
- Mössbauer spectroscopy was employed to analyze magnetic properties.
Main Results:
- HRTEM revealed numerous defects, including low-angle grain boundaries, within the goethite nanoparticles.
- These defects create magnetic mismatches between nanograins, weakening inter-grain magnetic coupling.
- The observed Mössbauer data are consistent with fluctuations in sublattice magnetization directions within these weakly coupled grains.
Conclusions:
- Defects, particularly low-angle grain boundaries, are responsible for the observed magnetic behavior and Mössbauer spectral anomalies in goethite nanoparticles.
- The findings suggest that defects significantly influence magnetic properties in other antiferromagnetic nanograin systems.
- This research provides insights relevant to Mössbauer studies of related materials like α-Fe(2)O(3) and α-Fe(2)O(3)/NiO nanoparticles.
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