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Surface spin disorder and spin-glass-like behaviour in manganese-substituted cobalt ferrite nanoparticles
Ist Teil von
Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology, 2012-10, Vol.14 (10), p.1-16, Article 1156
Ort / Verlag
Dordrecht: Springer Netherlands
Erscheinungsjahr
2012
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Manganese-substituted cobalt ferrite nanoparticles coated with triethylene glycol (TREG) have been prepared by the glycothermal reaction. The effect of Mn substitution and coating on temperature-dependent magnetic properties of the TREG-coated Mn
x
Co
1−
x
Fe
2
O
4
nanoparticles (0.0 ≤
x
≤ 0.8) with size of ~5–7 nm has been investigated in the temperature range of 10–300 K in a magnetic field up to 9 T. After the irreversible processes of the magnetic hysteresis curves were completed, the high-field regions of these curves were fitted by using a ‘law of approach to saturation’ to extract the magnetic properties, such as the effective anisotropy constant (
K
eff
) and the anisotropy field (
H
A
) etc. High coercive field of 12.6 kOe is observed in pure cobalt ferrite coated with TREG at 10 K. The low temperature unsaturated magnetization behaviour indicates the core–shell structure of the Mn
x
Co
1−
x
Fe
2
O
4
NPs. Zero-field-cooled (ZFC) and field-cooled (FC) measurements revealed superparamagnetic phase of TREG-coated Mn
x
Co
1−
x
Fe
2
O
4
nanoparticles at room temperature. The blocking and irreversibility temperatures obtained from ZFC–FC curves decrease at highest Mn concentration (
x
= 0.8). The existence of spin-glass-like surface layer with freezing temperature of 215 K was established with the applied field dependence of the blocking temperatures following the de Almeida–Thouless line for the Mn
0.6
Co
0.4
Fe
2
O
4
NPs. The shifted hysteresis loops with exchange bias field of 60 Oe and high-field irreversibility up to 60 kOe in FC
M
–
H
curve at 10 K show that spin-glass-like surface spins surrounds around ordered core material of the Mn
0.6
Co
0.4
Fe
2
O
4
NPs. FMR measurement show that all the TREG-coated Mn
x
Co
1−
x
Fe
2
O
4
nanoparticles absorb microwave in broad field range of about ten thousands Oe. The spectra for all the samples have broad linewidth because of angular distributions of easy axis and internal fields of nanoparticles.