Journal
JOURNAL OF APPLIED PHYSICS
Volume 116, Issue 5, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.4891497
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Funding
- Collectivites Locales, Le Mans Metropole-Departement de la Sarthe
- ISCR transversal Project
- Centre de Competence C'Nano Nord-Ouest
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Structural and magnetic properties of gamma-Fe2O3 nanoparticles of 4 nm diameter, dispersed into silica SiO2 matrix with a wide range value of volume fraction (0.05 to 1), were investigated. Produced gamma-Fe2O3@SiO2 nanocomposites consist of an assembly of very small single domain magnetic object (<10 nm) with a random distribution of both inter-particle distance and direction of particle magnetic moment. We focused on the determination of a magnetic percolation threshold, defined as the magnetic particles concentration value above which the magnetic properties of isolated particles vanished in favor of a magnetic collective behavior induced by magnetic interactions. A percolation threshold value of 0.63 was obtained by a local probe technique such as Fe-57 Mossbauer spectrometry and confirmed by global magnetic measurements through zero-field cooled, field-cooled, and ac susceptibility data. Below this threshold, dynamic ac magnetization measurements show a thermally activated Arrhenius dependence of the blocking temperature of superparamagnetic nanoparticles and above this critical value, one observes a slowing down of their dynamic properties, which lead toward the establishment of a spin-glass like state. (C) 2014 AIP Publishing LLC.
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