Preparation and magnetic properties of amorphous Co–Zr–B alloy nano-powders

The magnetic Co–Zr–B amorphous alloy powders, having a nearly spherical morphology with diameters <50 nm, were obtained successfully by the reduction of an aqueous solution of zirconium sulphate and cobalt chloride with an aqueous solution of sodium borohydride. XRD, selected-area electron diffraction (SAED) and differential scanning calorimetry (DSC) studies showed that the resultant were partially amorphous together with a tiny volume fraction of crystalline phases, and the main amorphous phase consisted of the Zr-based amorphous particles and the Co-based Zr-containing amorphous particles. It is found that the Co/Zr ratio in the powders was indistinguishably equal to the Co2+/Zr4+ ratio in the original mixed solution and the boron content of the samples increased along with the addition rate of NaBH4 solution. The crystallization temperatures of the resultant powders were in the range of 765.1–771.3 K. The thermal stability of amorphous Co–Zr–B powder increased with increasing the zirconium content. When the Co/Zr ratio in the samples increased from 1.94 to 5.14, the saturation magnetization increased monotonously from 4.76 to 8.87 emu/g, but the coercivity increased irregularly from 15.98 to 26.81 Oe.