INVESTIGADORES
DE BIASI Emilio
artículos
Título:
Surface effects in the magnetic properties of crystalline 3 nm ferrite nanoparticles chemically synthesized
Autor/es:
E. LIMA JR.; E. DE BIASI; M. VÁSQUEZ MANSILLA; M. E. SALETA; F. EFFENBERG; L. M. ROSSI; R. COHEN ; H. R. RECHEMBERG; R. D. ZYSLER
Revista:
JOURNAL OF APPLIED PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Año: 2010 vol. 108 p. 103919 - 103929
ISSN:
0021-8979
Resumen:
We have systematically studied the magnetic properties of ferrite
nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain
size distributions. Samples were prepared by the thermal decomposition
of Fe(acac)3
in the presence of surfactants giving nanoparticles covered by oleic
acid. High resolution transmission electron microscopy (HRTEM) images
and XRD diffraction patterns confirms that all samples are composed by
crystalline nanoparticles with the spinel structure expected for the
iron ferrite. ac and dc magnetization measurements, as well in-field
Mössbauer spectroscopy, indicate that the magnetic properties of
nanoparticles with 11 and 7 nm are close to those expected for a
monodomain, presenting large MS (close
to the magnetite bulk). Despite the crystalline structure observed in
HRTEM images, the nanoparticles with 3 nm are composed by a magnetically
ordered region (core) and a surface region that presents a different
magnetic order and it contains about 66% of Fe atoms. The high
saturation and irreversibility fields in the M(H)
loops of the particles with 3 nm together with the misalignment at 120
kOe in the in-field Mössbauer spectrum of surface component indicate a
high surface anisotropy for the surface atoms, which is not observed for
the core. For T<10 K,
we observe an increase in the susceptibility and of the magnetization
for former sample, indicating that surface moments tend to align with
applied field increasing the magnetic core size.