Preparation and characterization of cobalt carbides coated with NiCo with exchange-spring behavior

Abstract In this work, the synthesis of a new superparamagnetic composite of cobalt carbide coated with NiCo is reported. The carbide was synthesized by the polyol-assisted thermal decomposition method and coated with NiCo applying the electroless plating method. The coating time was varied in order to obtain the highest saturation magnetization. The carbide and the composite were characterized employing the following techniques: SEM-EDS, TEM, DSC, VSM, XRD, and CV. An exchange-spring magnet with much higher saturation magnetization than the starting carbide was obtained. The saturation magnetization of the starting carbide was 18 emu g −1 and the coated composite reached a saturation magnetization of 45 emu g −1 , that is, more than the double that of the initial carbide. The working temperature of the composite was calculated to be 350 °C. This method of obtaining rare earth-free materials is of relatively low cost and no toxic compounds are produced.