Synthesis of orientated Ni0.89Fe0.11/polymer nanofibres with a bimodal nanoparticle size distribution by electrospinning and thermal processing

Orientated ferromagnetic Ni0.89Fe0.11 nanoparticle/polymer nanofibres were made by electrospinning a solution containing iron(III) nitrate nonahydrate, nickel(II) acetate tetrahydrate, polyvinylpyrrolidone, and acetic acid in methanol and thermally processed in Ar and then 95%Ar:5%H2 up to 620 °C. There was a distribution in nanofibre widths after electrospinning with wider (average width 440 nm) and some thinner (average width 120 nm) nanofibres. The nanofibre width distribution decreased after heat treatment and the average nanofibre width reduced to 160 nm. A bimodal Ni0.89Fe0.11 nanoparticle size distribution was found where there were large surface nanoparticles with a mean diameter of 35 nm and small inner nanoparticles with a 5 nm mean diameter. There was a small spin-disordered shell magnetization that was only ~2% of the total 5 K saturation magnetization and a characteristic spin-freezing temperature of 21 K. The high field magnetization was large, and it reached 41.7 Am2/kg at 5 K.