NDLI: Finite size and surface effects on the magnetic properties of cobalt ferrite nanoparticles

Content Provider	Springer Nature Link
Author	Vázquez Vázquez, C. López Quintela, M. A. Buján Núñez, M. C. Rivas, J.
Copyright Year	2010
Abstract	Cobalt ferrite, CoFe$_{2}$O$_{4}$, nanoparticles in the size range 2–15 nm have been prepared using a non-aqueous solvothermal method. The magnetic studies indicate a superparamagnetic behavior, showing an increase in the blocking temperatures (ranging from 215 to more than 340 K) with the particle size, D $_{TEM}$. Fitting M versus H isotherms to the saturation approach law, the anisotropy constant, K, and the saturation magnetization, M $_{S}$, are obtained. For all the samples, it is observed that decreasing the temperature gives rise to an increase in both magnetic properties. These increases are enhanced at low temperatures (below ~160 K) and they are related to surface effects (disordered magnetic moments at the surface). The fit of the saturation magnetization to the T $^{2}$ law gives larger values of the Bloch constant than expected for the bulk, increasing with decreasing the particle size (larger specific surface area). The saturation magnetization shows a linear dependence with the reciprocal particle size, 1/D $_{TEM}$, and a thickness of 3.7 to 5.1 Å was obtained for the non-magnetic or disordered layer at the surface using the dead layer theory. The hysteresis loops show a complex behavior at low temperatures (T ≤ 160 K), observing a large hysteresis at magnetic fields H > ~1000 Oe compared to smaller ones (H ≤ ~1000 Oe). From the temperature dependence of the ac magnetic susceptibility, it can be concluded that the nanoparticles are in magnetic interaction with large values of the interaction parameter T $_{0}$, as deduced by assuming a Vogel–Fulcher dependence of the superparamagnetic relaxation time. Another evidence of the presence of magnetic interactions is the almost nearly constant value below certain temperatures, lower than the blocking temperature T $_{b}$, observed in the FC magnetization curves.
Starting Page	1663
Ending Page	1676
Page Count	14
File Format	PDF
ISSN	13880764
Journal	Journal of Nanoparticle Research
Volume Number	13
Issue Number	4
e-ISSN	1572896X
Language	English
Publisher	Springer Netherlands
Publisher Date	2010-04-16
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Cobalt ferrite Magnetic nanoparticle Superparamagnetism Nanoferrite Saturation approach law Anisotropy constant Interparticle interactions AC susceptibility Characterization and Evaluation of Materials Optics, Optoelectronics, Plasmonics and Optical Devices Nanotechnology Physical Chemistry Inorganic Chemistry
Content Type	Text
Resource Type	Article
Subject	Chemistry Nanoscience and Nanotechnology Atomic and Molecular Physics, and Optics Condensed Matter Physics Bioengineering Modeling and Simulation

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