Preparation of cobalt substituted zinc ferrite nanopowders via auto-combustion route: an investigation to their structural and magnetic properties

Co x Zn 1−x Fe 2 O 4 ( x = 0, 0.1, 0.2, 0.3, 0.4) nanopowders were fabricated via auto-combustion synthesis followed by calcined treatment. The structural, morphological, compositional and magnetic properties of the as-synthesized samples were decided by X-ray diffraction (XRD), field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, specific surface area and Physical Property Measurement System analyses, respectively. The XRD patterns revealed all annealed cobalt substituted zinc nanoferrites display a single phase cubic spinel structure, the decrease in lattice constant with increasing Co 2+ ions concentration is related to the lattice shrinkage originated from the replacement of Zn 2+ ions (ionic radii of 0.82 Å) by Co 2+ ions (ionic radii of 0.78 Å); the increase of crystallite size with increasing Co 2+ ions content can be attributed to the less exothermic for the formation of cobalt ferrite than that for zinc ferrite. The M – H curves revealed that there are unsaturated magnetization and negligible hysteresis loops for all samples with lower cobalt concentration ( x = 0, 0.1, 0.2, and 0.3), implying a superparamagnetic behavior; while the Co 0.4 Zn 0.6 Fe 2 O 4 nanoparticles ( x = 0.4) show ferromagnetism at room temperature. The M–T relations inferred the substitution of cobalt ions can remarkably enhance Curie temperature of the as-prepared Co–Zn ferrite nanoparticles. At room temperature lower cobalt-substituted zinc nanoferrites tend to show superparamagnetism while higher cobalt-substituted zinc nanoferrites prefer to present ferromagnetism.