Abstract
Recent advances in the field of magnetic materials emphasize that the development of new and useful magnetic nanoparticles (NPs) requires an accurate and fundamental understanding of their collective magnetic behavior. Studies show that the magnetic properties are strongly affected by the magnetic anisotropy of NPs and by interparticle interactions that are the result of the collective magnetic behavior of NPs. Here we study these effects in more detail. For this purpose, we prepared CoxFe3−xO4 NPs, with x = 0–1 in steps of 0.2, from soft magnetic (Fe3O4) to hard magnetic (CoFe2O4) ferrite, with a significant variation of the magnetic anisotropy. The phase purity and the formation of crystalline NPs with a spinel structure were confirmed through Rietveld refinement. The effect of Co doping on structure, morphology and magnetic properties of CoxFe3−xO4 samples was investigated. In particular, we examined the interparticle interactions in the samples by δm graphs and Henkel plots that have not been reported before in literature. Finally, we studied the hyperthermia properties and observed that the heat efficiency of soft Fe3O4 is about 4 times larger than that of hard CoFe2O4 ferrite, which was attributed to the high coercive field of samples compared with the external field amplitude.
Highlights
Technological advances in various fields have motivated the design and the fabrication of nanostructures with tuned and improved properties
The heating efficiency of the NPs as heat sources under ac magnetic fields is often denominated as specific absorption rate (SAR), which is directly related to the area of the magnetic hysteresis loop of the nanoparticles by the following formula [18,19]: (1)
We studied the effect of Co doping on the structural, magnetic and hyperthermia properties of CoxFe3−xO4 nanoparticles
Summary
Technological advances in various fields have motivated the design and the fabrication of nanostructures with tuned and improved properties. The thickness of the surface dead layer (t) equaling to t = 0.56 and 0.26 nm for the samples Fe3O4 and CoFe2O4, respectively, was obtained as follows [34,35]: To calculate Keff, the experimental curves of M as a function of 1/H2 were fitted by Equation 6 at high magnetic field strengths (Figure 9).
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