Nanostructured nickel manganese oxide: Aligned nanostructures and their magnetic properties

The present study describes the control of the assembly of NiMn ₂O ₄ nanospheres and hexagonal particles by tuning the precursor (nickel manganese oxalate) morphology. The aspect ratio (2 to 24) of the nickel manganese oxalate precursors has been achieved by the variation of the surfactant, co-surfactant and non-polar phase by the reverse micellar route. Slow decomposition of the oxalate precursor (aspect ratio ≥ 3) enables us to maintain the anisotropic morphology in the NiMn ₂O ₄ nanorods. However, the decomposition of the cuboid-shaped oxalate precursor (aspect ratio < 3) led to the formation of spherical nanoparticles. The ferrimagnetic transition temperature T _c (126-72 K) and magnetization decrease with the decrease in the aspect ratio of the nanorods. Hexagonal nanoparticles of NiMn ₂O ₄ show the lowest T _c (∼72 K) and magnetization.