D E Madsen et al 2009 J. Phys.: Condens. Matter 21 016007 doi:10.1088/0953-8984/21/1/016007
Magnetic fluctuations in nanosized goethite (α-FeOOH) grains
D E Madsen1, L Cervera-Gontard2, T Kasama3, R E Dunin-Borkowski2, C B Koch4, M F Hansen5,6, C Frandsen1 and S Mørup1
Show affiliationsMössbauer spectra of antiferromagnetic goethite (α-FeOOH) particles usually show an asymmetric line broadening, which increases with increasing temperature, although the magnetic anisotropy is expected to be so large that magnetic relaxation effects should be negligible. By use of high resolution transmission electron microscopy we have studied a sample of goethite particles and have found that the particles contain many defects such as low angle grain boundaries, in accordance with previous studies of other samples of goethite particles. Such defects can result in a magnetic mismatch at the grain boundaries between nanometer-sized grains, leading to a weakened magnetic coupling between the grains. We show that the Mössbauer data of goethite can be explained by fluctuations of the sublattice magnetization directions in such weakly coupled grains. It is likely that the influence of defects such as low angle grain boundaries also plays a role with regards to the magnetic properties in other antiferromagnetic nanograin systems. We discuss the results in relation to Mössbauer studies of α-Fe2O3 and α-Fe2O3/NiO nanoparticles.
- PACS
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75.50.Tt Fine-particle systems; nanocrystalline materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
68.37.Lp Transmission electron microscopy (TEM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
- Subjects
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Condensed matter: electrical, magnetic and optical
- Dates
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Issue 1 (7 January 2009)
Received 23 September 2008, in final form 10 November 2008
Published 8 December 2008
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Magnetic fluctuations in nanosized goethite (α-FeOOH) grains
D E Madsen et al 2009 J. Phys.: Condens. Matter 21 016007
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A compilation of data on two-photon reactions
M R Whalley 2001 J. Phys. G: Nucl. Part. Phys. 27 A1
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Calculation of the microcanonical temperature for the classical Bose field
M J Davis and P B Blakie 2005 J. Phys. A: Math. Gen. 38 10259
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A Machian model of dark energy
R G Vishwakarma 2002 Class. Quantum Grav. 19 4747
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Coupled oscillators, entangled oscillators, and Lorentz-covariant harmonic oscillators
Y S Kim and Marilyn E Noz 2005 J. Opt. B: Quantum Semiclass. Opt. 7 S458
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