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

摘要

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 Co~(2+)/Zr~(4+) ratio in the original mixed solution and the boron content of the samples increased along with the addition rate of NaBH_4 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.