Heat treatment on Ni and Cr-doped Ni core-shell nanoparticle granular films

Structural and magnetic property changes of heat treated Nickel (Ni) and 5% Chromium-doped Nickel (5Cr-Ni) nanoparticle (NP) granular films were studied. These films were prepared by allowing the core-shell NPs to deposit on 8 mm × 8 mm silicon substrates using a nanocluster deposition system. The as-prepared Ni core-shell NP granular films showed saturation magnetization (M_s) of ~23.8 emu/g, magnetic remanence (M_r) of ~0.16 emu/g and coercivity (H_c) of ~4.5 Oe. On the other hand, the as-prepared 5Cr-Ni core-shell NP granular films showed M_s of ~7.6 emu/g, M_r of ~0.2 emu/g and H_c of ~8 Oe. Transmission Electron Microscopy measurement shows that, the average particle size of the core-shell Ni and 5Cr-Ni NPs in the as-prepared granular films is around ~20 nm. Heat treatment at 600°C for 30 min under the constant flow of Argon gas increased the average particle size of both Ni and 5Cr-Ni NPs to 50 nm. The saturation magnetization, magnetic remanence and coercivity also increased under the influence of heat treatment in both the cases. The increase in magnetic properties of the 5Cr-Ni granular film is high compared to the increase in magnetic properties of the Ni NP granular film. The presence of Cr in Ni is reported to be the cause for better enhancement of the magnetic properties in 5Cr-Ni films after heat treatment. The X-ray diffraction confirms the presence of Ni and NiO in the films. Energy-dispersive X-ray spectroscopy measurements confirm the presence of Cr in the 5Cr-Ni samples. The enhancement of magnetic properties was also found to be due to particle growth and aggregation, and it is confirmed by scanning electron microscopy images.