ZnFe₂O₄/CuO core–shell structured nanoparticles: synthesis, structural and magnetic properties

Synthesis of core/shell structured ZnFe₂O₄/CuO nanoparticles with varying core diameter and different weight percentage of CuO phase [(1−x) ZnFe₂O₄/x CuO: x = 0.15, 0.30, 0.45 and 0.60] using double stage standard chemical co-precipitation method has been reported in this article. For first four samples only the diameter of core was varied and for other four samples only the weight percentage of CuO phase was varied. The existence of both cubic spinel ZnFe₂O₄ phase along with monoclinic CuO phase was verified by X-ray patterns recorded at room temperature. The average core diameter was in between 8 and 13 nm as estimated using Scherrer's formula and further verified by HRTEM images. A reduction in lattice parameter with increasing core thickness and also with increasing CuO phase was observed. A notable enhancement in coercivity and saturation magnetization were observed in field cooled (5 T) hysteresis loops obtained at 5 K for the first four varying core diameter core–shell structured nanoparticles in comparison to bare zinc ferrite nanoparticles of almost same size. A decreasing trend in coercivity and saturation magnetization was also noticed in low temperature hysteresis loops for higher CuO content samples. A considerable improvement in blocking temperature (T_B) as well as Néel temperature (T_N) for all the different core diameter samples were also found in M(T) protocols. Both blocking temperature and Néel temperature decreased for increasing CuO content in composite nanoparticles. The room temperature M(H) plots exhibited superparamagnetic nature with insignificant coercivity and negligible remanence.