The effect of magneto-crystalline anisotropy on the properties of hard and soft magnetic ferrite nanoparticles

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 Co _x Fe_{3- x} O₄ 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 Co _x Fe_{3- x} O₄ 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.