Magnetic properties of monodisperse iron oxide nanoparticles

Abstract

We have synthesized a set of monodisperse iron oxide nanoparticles ranging from 7.8to17.9nm by thermal decomposition methods. Based on the evidence of high-resolution transmission electron microscopy, the iron oxide nanoparticles appear as spherical dots with size standard deviations of less than 5%. Blocking temperatures of the set of nanoparticles were measured by the zero-field-cooled magnetization measurements. The anisotropy energy constants are estimated from the measured blocking temperatures. The contribution from the surface anisotropy is the dominant factor of the higher anisotropy energy found. The saturation magnetization and coercive force HC (77K) are functions of the particle size and increase with the particle size.

Spin dynamics and criteria for onset of exchange bias in superspin glass Fe/γ-Fe2O3core-shell nanoparticles

“…The ZFC curve shows a conventional peak (T P-ZFC ~ 69K) which has been reported in many superparamagnetic (SPM) and superspin glass (SSG) systems that are ferromagnetic in the ground state [20][21][22] . The peak in ZFC curve for monodispersed, non-interacting particles, is called the blocking temperature (T B ) and is found to occur when the thermal energy (k B T) is comparable to the activation energy (ΔE A =KV) 23 .…”

Influence of synthesis experimental parameters on the formation of magnetite nanoparticles prepared by polyol method

“…The nanoparticles also presented coercivity (H c ) at 85 K, indicating a ferrimagnetic regimen [30]. It is well known that at temperatures below the blocking temperature (T<T B ), H c increases with the decreasing of the temperature [40]. Since the values of H c of MM samples are near to zero, the T B of these samples is slightly greater than 85 K. Since the values of H c of samples CM are greater than the corresponding ones to samples MM, the T B of samples CM should be higher than those of samples MM.…”

Thermomagnetic determination of Fe3O4 magnetic nanoparticle diameters for biomedical applications

“…To address considerations (i) and (ii) in this work, a small applied field of H appl ¼50 Oe was applied following zero-field-cooling, which is well below the anisotropy field of iron oxide H K ¼1200-1400 Oe [45,46]. To address considerations (ii) interparticle dipole interactions and (iii) cubic anisotropy in the iron oxide NPs an effective anisotropy constant K eff was utilized that includes several anisotropy contributions, including magnetocrystalline anisotropy, shape anisotropy, surface anisotropy, and dipole-dipole interactions between MagNPs; the effective anisotropy concept is commonly employed in the context of MagNP ensembles [47][48][49]. With these considerations in mind, it is possible to apply the thermomagnetic characterization method to the materials of this study and obtain useful information.…”