Electroless Ni–Co–P ternary alloy deposits: preparation and characteristics

Electroless Ni–Co–P ternary alloy deposits were prepared by varying the metallic ratio and were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and vibration sample magnetometer. The plating rate of electroless Ni–Co–P deposits is a function of concentration of sodium hypophosphite, pH of the plating bath, plating time and the metallic ratio. With increase in metallic ratio, the cobalt content of the deposits increases with a simultaneous decrease in the nickel content, while the phosphorus content decreases slightly. The electroless Ni–Co–P deposits of the present study are amorphous in their as-deposited condition. The DSC trace exhibits three distinct exothermic peaks, corresponding to the relaxation of lattice strain during the phase separation, the phase transformation of amorphous phase to nickel and nickel phosphide phases and the transformation of metastable phases to stable nickel phosphide phase. The XRD pattern of electroless Ni–Co–P deposits confirms the formation of Ni, Ni5P2, Ni12P5 and Ni3P phases during annealing at 300 and 400 °C for 1 h. Thermomagnetic study exhibits the Curie transition of nickel and non-stoichiometric Ni3Co based alloys. Being amorphous in nature, the electroless Ni–Co–P deposits exhibit soft magnetic characteristics. The saturation magnetization, remanence and coercivity increase with cobalt content of the deposit.