# name
Finite-size and surface effects in maghemite nanoparticles: Monte Carlo simulations

# metadata.dc.description.abstract[].value
Finite-size and surface effects in fine particle systems are investigated by Monte Carlo simulation of a model
of a g-Fe2O3 ~maghemite! single particle. Periodic boundary conditions for a large enough system have been
used to simulate the bulk properties and the results compared with those for a spherical shaped particle with
free boundaries to evidence the role played by the surface on the anomalous magnetic properties displayed by
these systems at low temperatures. Several outcomes of the model are in qualitative agreement with the
experimental findings. A reduction of the magnetic ordering temperature, spontaneous magnetization, and
coercive field is observed as the particle size is decreased. Moreover, the hysteresis loops become elongated
with high values of the differential susceptibility, resembling those from frustrated or disordered systems.
These facts are a consequence of the formation of a surface layer with higher degree of magnetic disorder than
the core, which, for small sizes, dominates the magnetization processes of the particle. However, in contradiction
with the assumptions of some authors, our model does not predict the freezing of the surface layer into
a spin-glass-like state. The results indicate that magnetic disorder at the surface simply facilitates the thermal
demagnetization of the particle at zero field, while the magnetization is increased at moderate fields, since
surface disorder diminishes ferrimagnetic correlations within the particle. The change in shape of the hysteresis
loops with the particle size demonstrates that the reversal mode is strongly influenced by the reduced atomic
coordination and disorder at the surface.

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Reproducció digital del document publicat en format paper, proporcionada per PROLA i http://dx.doi.org/10.1103/PhysRevB.63.184416

# metadata.dc.source[].value
Articles publicats en revistes (Física de la Matèria Condensada)

# metadata.dc.title[].value
Finite-size and surface effects in maghemite nanoparticles: Monte Carlo simulations