Nanostructured nickel manganese oxide: aligned nanostructures and their magnetic properties

Abstract

The present study describes the control of the assembly of NiMn₂O₄ 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 NiMn₂O₄ 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 NiMn₂O₄ show the lowest T_c (∼72 K) and magnetization.