Fluoride ion assisted growth of hierarchical flowerlike nanostructures of Co/Ni ferrites and their magnetoresistive response

Abstract

One-dimensional nanorod arrays exhibiting hierarchical flowerlike morphologies, of Co and Ni based ferrites were synthesized by hydrothermal treatment and using ammonium fluoride (NH₄F) as a mineralizing agent. The effects of NH₄F concentration and synthesis temperature were probed to control the morphology of these nanorods that were formed as a result of crystal nucleation. It was observed that a higher concentration of NH₄F leads to several other nucleation sites above these nanorods while controlled concentration of precursors and NH₄F results in the synthesis of floral patterns. The specific geometries of these nanorods leads to a shape anisotropy effect resulting in increased magnetic coercive fields. To study the effect of magnetic field on the resistance and current density, impedance spectroscopy and I–V–R characteristics, respectively, were performed. Nanorods show enhanced values for resistance with the increase in magnetic field confirming the effect of magnetoresistive coupling while a decrease in current densities with increasing magnetic field highlights the potential of these structures for magnetoresistive applications.