Exploring the Effect of Co Doping in Fine Maghemite Nanoparticles

Abstract

We present a study of the structural, magnetic, and magneto-optical properties of a series of Co-substituted ferrite nanoparticles (NPs) prepared by thermal decomposition of metallo-organic precursors in high boiling solvents. The structural characterization, carried out by using several techniques (transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and magnetic circular dichroism measurements), showed all the samples are high crystalline, 5–6 nm spherical NPs with the cubic spinel structure typical of ferrites. The evolution of lattice parameters with cobalt content suggests that the material is Co-substituted maghemite, also confirmed by XAS and magneto optical (MO) characterizations. The investigation of the magnetic and magneto-optical properties displays peculiar trends with the cobalt content, the main features being the large increase of the saturation magnetization and the anomalous dependence of magnetic anisotropy which reaches its maximum values for intermediate compositions. The large tuneability of this material makes it possible to implement the performances of devices used in biomedical and sensing applications

Influence of cobalt doping on the hyperthermic efficiency of magnetite nanoparticles

“…5b) show that the maximum of the magnetic anisotropy is reached at x¼0.6. This result nicely confirms the one we previously observed on investigating the magnetic properties of a family of 5 nm maghemite NPs doped with different amount of Co [22]. Moreover, since the trend of K matches that of the remanence, it can be argued that K is mainly driven by the magneto-crystalline contribution, supporting the idea that such behavior is an intrinsic property of the doped nanomaterial.…”

“…Indeed, in a recent study of Co-doped NPs grown in the internal cavity of functionalized human ferritin, some of us demonstrated that a small amount of doping (5% w/w) was enough to strongly enhance the hyperthermic efficacy on melanoma cells with respect to the undoped samples, without compromising the cytotoxicity of the material [21]. Moreover, some of us reported that the magnetic anisotropy of 5 nm Co x Fe (8/3 À 2/3x) O 4 NPs does not increase monotonously with Co reaching a maximum for intermediate composition (x ¼0.6) [22]. These results suggest the possibility to reduce significantly the Co content while achieving performances that match and even outclass those of stoichiometric cobalt ferrite.…”

Iron Oxide Based Nanoparticles for Multimodal Imaging and Magnetoresponsive Therapy

“…441 Therefore, an increase in the K value can be simply achieved via the substitution of ferrous ions with more anisotropic ions, such as nickel or cobalt ions. 512,513 For example, the total replacement of Fe 2+ with Co 2+ allows the magnetic anisotropy to become 20 times higher than that of pristine magnetite (Figure 21b). 513 On the nanoscale dimension, surface contributions to magnetic properties become important because of the high surface-to-volume ratio.…”

CHAPTER 4. Functionalized Magnetic Nanoparticles for Heavy Metals Removal from Aqueous Solutions

“…66,82 Thermal decomposition methods can be used for the synthesis of magnetic nanoparticles. A thermal decomposition route appears to be the best synthesizing method for controlling shape and size of magnetic nanoparticles.…”