We find three unanticipated features in the magnetic response of dilute systems of highly monodisperse Fe nanoparticles. Above a spin freezing temperature (Tf) the remanent magnetization relaxes smoothly to zero, but below Tf the relaxation halts abruptly at a nonzero value. The distribution of relaxation rates changes at a percolation temperature (Tp), consistent with chainlike structures above Tp and three-dimensional clusters below Tp. The blocking temperature (Tb) 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 - Nov 1 2002|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics