Enhanced Magnetic Properties of Ni-Co Alloy nanoparticles

Abstract

A mono-layer of Ni-Co alloy nanoparticles was fabricated on a polyimide (PI) film via deposition of a 3.5-nm-thick Co thin film on top of preexisting nano-sized Ni particles followed by thermal annealing. The preexisting 5-nm-sized Ni nanoparticles were produced on the PI thin film by imidizing a PI precursor layer with a Ni80Fe20 thin film on top of the precursor. The average particle size of the thus-fabricated Ni-Co alloy particles ranged from 5 nm to 9 nm depending on the heat treatment conditions. In general, the Ni-Co alloy particles exhibited a dramatic increase in saturation magnetization, particularly when the samples were annealed through rapid thermal annealing (RTA), as the thermal energy was efficiently delivered to the nanoparticles by RTA. The blocking temperature of the nanoparticles also increased to 230 K as Co was successfully incorporated into the Ni nanoparticles using RTA.