Microwave characteristics of low density hollow glass microspheres plated with Ni thin-film

Hollow glass microspheres coated with thin Ni films of various thicknesses (about 50-250 nm) were obtained by electroless plating technique. The resultant magnetic microspheres had very low densities (similar to 0.39-1.28 g cm(-3)) and low coercivities (< 40 Oe). As-plated films comprised of nanocrystallites embedded in amorphous matrix and postannealing treatment led to a submicrocrystalline structure and an increased saturation magnetization. The high frequency properties of the composites consisting of Ni-plated microspheres and polymer were investigated. The permittivity and permeability increased with increasing microsphere content in the composite and increasing Ni film thickness. These composites had ferromagnetic resonance peak in the range of 5-12 GHz. Postannealing also had an effect on the microwave properties. The reflection loss of the composite was found dependent on the absorber material thickness, polymer:microsphere ratios, the Ni film thickness, as well as the heat treatment of the microspheres. (c) 2006 American Institute of Physics.