Preparation and magnetic properties of amorphous Co-Fe-B nanoparticles

Amorphous Co-Fe-B nanoparticles coated with PVP (polyvinyl pyrrolidone) were prepared by reduction of metal ions in aqueous solution by use of NaBH4 at room temperature. The size of nanoparticles was in the range of 10-20 nm and from the XRD patterns, these nanoparticles were amorphous. FE-SEM-WDX analyses showed the B content to be in the range of 38-45 at%. The saturation magnetization and coercivity for the samples was in the range of 45-50 emug ¹ and 31-110 Oe, respectively. The composites of nanoparticles with the minimum coercivity and PVP as the binder (particle weight percent 75 wt.%) showed permeability of μ"_{r max} 1.9 at 0.7 GHz and a good microwave absorption property (reflection loss: RL < -20 dB).