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The low-temperature dynamics of a magnetic nanoparticle system (gama-Fe2O3-alginate nanocomposite with average particle size around 4 nm) are studied superconducting quantum interference device measurements. Observations indicate that the dynamics of this nanoparticle system are governed a wide distribution of particle relaxation times.

The low-temperature dynamics of a magnetic nanoparticle system (γ-Fe2O3-alginate nanocomposite with average particle size around 4 nm) have been studied by superconducting quantum interference device measurements. Using different temperature and field protocols, memory phenomena in the dc magnetization and magnetic relaxation have been observed at temperatures below its blocking temperature TB=37 K. However, aging experiments show an absence of any waiting time dependence in the magnetization relaxation. These observations indicate that the dynamics of this nanoparticle system are governed by a wide distribution of particle relaxation times which arise from the distribution of particle sizes and weak interparticle interactions. [ABSTRACT FROM AUTHOR]

We have investigated interaction effects in two different systems of iron oxide nanoparticles. Samples of γ-Fe2O3 and Fe3O4 nanoparticles were synthesized using a matrix-mediated precipitation reaction and a chemical co-precipitation technique respectively. The structural properties of these nanoparticles were studied using x-ray diffraction and transmission electron microscopy. We also used temperature dependent ac magnetic susceptibility measurements to carefully investigate the interactions among these nanoparticles. Our analysis showed that the characteristic interaction energy does not depend simply on the average spacing between the nanoparticles but is likely to be strongly influenced by the fluctuations in the nanoparticle distribution. [ABSTRACT FROM AUTHOR]