High-frequency magnetic properties of Ni-Zn ferrite nanoparticles synthesized by a low temperature chemical method
Graphical Abstract
Highly crystalline Ni-Zn ferrite NPs, which were synthesized by a room temperature co-precipitation method, demonstrate a broad peak of μ' ' in high frequency range. The NPs have the potential be to be used as microwave absorbers and effective heating mediators for hyperthermia application in cancer therapy.
Introduction
Nowadays, Spinel ferrite MFe2O4 (M = Ni, Co, Mn, Zn, etc.) NPs have attracted great interests because of their peculiar properties and various important applications such as magnetic data storage[1], magnetic drug delivery (e.g. transport of anticancer drugs, heat treatment of tumors) [2], [3], magnetic resonance imaging (MRI) [4], ferrofluids [5], microwave absorber [6] etc. For these potential applications, various methods have been proposed for the synthesis of spinel ferrite NPs in the past several years [7], [8], [9], [10], [11]. However, most of these methods need complicated synthetic steps, high reaction temperature and expensive or toxic reagents. Hence, exploration of simple and facile methods for large-scale synthesis of uniform spinel ferrite NPs is still of high interest. Especially for biomedical applications, it is often required that ferrite NPs are directly synthesized at room temperature without subsequent firing of the material. If we can realize room temperature synthesis of ferrite particles, we will be able to immobilize directly low heat-resistance biomolecules (enzyme, antibody, DNA, etc.) onto ferrite NPs. In addition, more and more electronic devices require non-heat-resistant substrate materials such as plastics and GaAs integrated circuits. Conventional ferrite preparation techniques often require high calcination temperatures (> 600 °C) for the crystallization of ferrites. This deteriorates the non-heat-resistant substrates and limits their uses in electronic devices. Thus, if we can directly synthesize ferrites at room temperature, we will be able to open new opportunities to fabricate devices using non-heat-resistant substrates such as organic materials or biomaterials.
In this work, highly crystalline Ni-Zn-ferrite NPs were successfully synthesized via a simple aqueous solution method at room temperature. Different from the previous work [12], the mixed solution of aqueous ammonia (NH3 ∙ H2O) and hydrazine hydrate (N2H4 ·H2O) was used as the precipitation agent. Another action of hydrazine hydrate was to slow down the oxidation of Fe2+ to Fe3+, thus improves the reproducibility of ferrite NPs. This approach is a one-step and simple method with comparatively high yield. The structure and magnetic properties of the resultant nanoparticles were characterized.
Section snippets
Experimental
A typical preparation procedure is as follows: 0.05 mol NiCl2·6H2O, 0.05 mol ZnCl2, 0.1 mol FeCl2·4H2O and 0.1 mol FeCl3·6H2O are dissolved into 200 ml deionized water. The molar ratios of Ni2+:Zn2+:Fe2+:Fe3+ are 1:1:2:2, which gives a composition of (Ni0.5Zn0.5)Fe2O4. With vigorous stirring, NH4OH and 0.5 ml hydrazine hydrate (N2H4·H2O, 80% concentration) solution are added to the solution drop by drop to keep the pH value of the mixture in the range 9~10. The stirring speed is fixed at about 800 rpm
Results and discussion
The X-ray diffraction pattern of the as-prepared sample is shown in Fig. 1. It is found that all the peaks could be indexed to a face-centered cubic Ni0.5Zn0.5Fe2O4 ferrite phase, which confirms that ferrite spinel phase is formed. No other impurity phases can be detected in the XRD patterns. The sharp and strong diffraction peaks also confirm the good crystallization of the products. The broaden peaks indicate that the as-prepared ferrite particles are very small. The line width analysis of
Conclusions
In summary, highly crystalline Ni-Zn ferrite NPs have been successfully synthesized by a low temperature co-precipitation method. The XRD and selected-area electron diffraction (SAED) pattern of the sample showed that the spinel-structured Ni-Zn ferrites are formed. The particles demonstrated soft magnetic properties. The saturation magnetization (Ms) was as high as about 60 emu/g and was comparable to the reported value of high temperatures annealed Ni-Zn ferrite. The imaginary part μ″ of the
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 30772220) and Young Teacher's Supporting Foundation of Xi'an Jiaotong University (No. 08141008).
References (14)
- et al.
J Magn Magn Mater
(1990) - et al.
J Magn Magn Mater
(2003) - et al.
Mater Res Bull
(2001) - et al.
Powder Technol
(2003) - et al.
Scripta Materialia
(2007) - et al.
J Phys D: Appl Phys
(2002) - et al.
Langmuir
(2008)