Abstract
In this paper, a series of experiments are reported where ferrite nanoparticles were synthesized with different substitution percentages (5, 10, 15, or 20%) of Fe2+ by Co2+, Mn2+, or Ni2+ ions. Afterwards, the prepared nanoparticles were thermally treated between 50 and 500 °C in air for 24 h in order to observe how doping influences the oxidation process induced by temperature elevation and access to O2. Nanoparticles were imaged before and after thermal treatment by transmission electron microscopy and were analyzed by X-ray diffraction, vibrating sample magnetometry, and Mössbauer spectroscopy. Presented studies reveal that the amount and kind of doped transition metals (of replaced Fe2+) strongly affect the oxidation process of ferrite nanoparticles, which can govern the application possibility. Each transition element suppresses the oxidation process in comparison to pure Fe-oxides, with the highest impact seen with Ni2+.
Highlights
It was reported that the surface anisotropy of nanoparticles modified by hematite causes a nonparallel arrangement of magnetic moments on the surface of nanoparticles
The synthesized ferrite nanoparticles were characterized by X-ray diffraction (XRD)
The data presented in this paper indicate that doping of magnetite by 3d elements influences its reactivity/resistance to the oxidative environment very strongly
Summary
Forecasted multifunctional applications cause great interest in the development and testing of different magnetic nanomaterials. Various nanoparticles exposed to AF fields will release a different amount of heat due to re-magnetization processes, based on the Néel effect (changing of magnetic moment direction without particle movement [16]). It was reported that the surface anisotropy of nanoparticles modified by hematite causes a nonparallel arrangement of magnetic moments on the surface of nanoparticles The presence of such layers influences the MNP response in an external AF field and is directly related to the heating capabilities of the particles. Gentle heat treatment in specific conditions can lead to the formation of very unique Fe-oxide forms, such as ε-Fe2 O3 or its derivatives The presence of this structure influences magnetic properties of the system [24]. Magnetic properties characterization of thermally treated nanoparticles was carried out along with estimation of their phase change
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