Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles

Kavli Affiliate: Paul Alivisatos

| First 5 Authors: Andreu Cabot, A. Paul Alivisatos, Victor F. Puntes, Lluis Balcells, Oscar Iglesias

| Summary:

In the present work, we investigate the magnetic properties of ferrimagnetic
and noninteracting maghemite (g-Fe2O3) hollow nanoparticles obtained by the
Kirkendall effect. From the experimental characterization of their magnetic
behavior, we find that polycrystalline hollow maghemite nanoparticles are
characterized by low superparamagnetic-to-ferromagnetic transition
temperatures, small magnetic moments, significant coercivities and
irreversibility fields, and no magnetic saturation on external magnetic fields
up to 5 T. These results are interpreted in terms of the microstructural
parameters characterizing the maghemite shells by means of an atomistic Monte
Carlo simulation of an individual spherical shell model. The model comprises
strongly interacting crystallographic domains arranged in a spherical shell
with random orientations and anisotropy axis. The Monte Carlo simulation allows
discernment between the influence of the structure polycrystalline and its
hollow geometry, while revealing the magnetic domain arrangement in the
different temperature regimes.

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