Nano Archive

Magnetic resonance in nanoparticles: between ferro- and paramagnetism

Noginova, N and Chen, F and Weaver, T and Giannelis, E P and Bourlinos, A B and Atsarkin, V A (2007) Magnetic resonance in nanoparticles: between ferro- and paramagnetism. Journal of Physics: Condensed Matter, 19 (24). 246208 (15pp).

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Magnetic nanoparticles of γ-Fe2O3 coated with organic molecules and suspended in liquid and solid matrices, as well as non-diluted magnetic fluid, have been studied by electron magnetic resonance (EMR) at 77–380 K. Slightly asymmetric spectra observed at room temperature become much broader and symmetric, and shift to lower fields upon cooling. An additional narrow spectral component (with a line-width of 30 G) is found in diluted samples; its magnitude obeys the Arrhenius law with an activation temperature of about 850 K. The longitudinal spin-relaxation time, T110 ns, is determined by a specially developed modulation method. The angular dependence of the EMR signal position in field-freezing samples points to substantial alignment, suggesting the formation of dipolar-coupled aggregates. The shift and broadening of the spectrum upon cooling are assigned to the effect of the surface-related anisotropy. To describe the overall spectral shape, the 'quantization' model is used which includes summation of resonance transitions over the whole energy spectrum of a nanoparticle considered as a giant exchange cluster. This approach, supplemented with some phenomenological assumptions, provides satisfactory agreement with the experimental data.

Item Type:Article
ID Code:5316
Deposited By:Prof. Alexey Ivanov
Deposited On:06 Aug 2009 11:25
Last Modified:06 Aug 2009 11:32

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