We find three unanticipated features in the magnetic response of dilute systems of highly monodisperse Fe nanoparticles. Above a spin freezing temperature (formula presented) the remanent magnetization relaxes smoothly to zero, but below (formula presented) the relaxation halts abruptly at a nonzero value. The distribution of relaxation rates changes at a percolation temperature (formula presented) consistent with chainlike structures above (formula presented) and three-dimensional clusters below (formula presented) The blocking temperature (formula presented) varies inversely proportional to particle diameter, opposite to the behavior of the Néel-Brown model for individual domains, but consistent with a type of Casimir-Polder interaction expected between dilute nanometer-scale particles.
|Original language||English (US)|
|Number of pages||4|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Jan 1 2002|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics