| Summary: | <p>Abstract</p> <p>Background</p> <p>Ni<sub>2</sub>O<sub>3</sub>- γ-Fe<sub>2</sub>O<sub>3</sub> composite nanoparticles coated with a layer of 2FeCl<sub>3</sub>·5H<sub>2</sub>O can be prepared by co-precipitation and processing in FeCl<sub>2</sub> solution. Using vibrating sample magnetometer (VSM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) diffraction techniques, the dependence of the preparation on the concentration of the FeCl<sub>2</sub> treatment solution is revealed.</p> <p>Results</p> <p>The magnetization of the as-prepared products varied non-monotonically as the FeCl<sub>2</sub> concentration increased from 0.020 M to 1.000 M. The Experimental results show that for the composite nanoparticles, the size of the γ-Fe<sub>2</sub>O<sub>3</sub> phase is constant at about 8 nm, the Ni<sub>2</sub>O<sub>3</sub> phase decreased and the 2FeCl<sub>3</sub>·5H<sub>2</sub>O phase increased with increasing concentration of FeCl<sub>2</sub> solution. The magnetization of the as-prepared products mainly results from the γ-Fe<sub>2</sub>O<sub>3</sub> core, and the competition between the reduction of the Ni<sub>2</sub>O<sub>3</sub> phase with the increase of the 2FeCl<sub>3</sub>·5H<sub>2</sub>O phase resulted in the apparent magnetization varying non-monotonically.</p> <p>Conclusions</p> <p>When the concentration of FeCl<sub>2</sub> treatment solution did not exceed 0.100 M, the products are spherical nanoparticles of size about 11 nm; their magnetization increased monotonically with increasing the concentration of FeCl<sub>2</sub> solution due to the decreasing proportion of Ni<sub>2</sub>O<sub>3</sub> phase.</p>
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