Controlled synthesis, phase formation, growth mechanism, and magnetic properties of 3-D CoNi alloy microstructures composed of nanorods

Abstract

3-D flower like CoNi alloys nanostructures composed of nanorods have been synthesized by template free hydrothermal method at relatively low temperature (120 °C). The detailed characterizations confirm the formation of good crystalline fcc CoNi alloy, average crystallite size of 18.8 ± 1.0 nm, lattice parameter of 3.531 ± 0.01 Å, and the nearly equiatomic composition (Co50Ni50). Highly uniform flower like nano structures are built up with nanorod of diameter about 100 nm and length in range of 200–400 nm. The nanorods (building blocks of flower) have single crystalline nature with [111] preferred growth direction. The concentration of NaOH plays a vital role in formation of alloys and high concentration promotes the formation of CoNi alloy at low temperature. The concentration of NaOH also affects the morphology remarkably by changing the growth/reaction rate of CoNi nanostructures and results in hollow spheres to nanoplate flower of CoNi alloys. Based on the evolution of the morphology of the products, a step wise growth mechanism is rationally proposed for flower like nanostructures by considering the effects of kinetic parameters on growth. Magnetic measurements show Co50Ni50 flower like nanostructure have high saturation magnetization, coercivity, remanent magnetization, and high effective anisotropy constant of value 101.3 emu g−1, 210.5 Oe, 16.2 emu g−1, and 4.457 × 104 J m−3 respectively. The enhancements of coercivity and effective anisotropy constant are attributed to nanoscale effects such as shape/surface anisotropy.