Fe/ferrite composite magnetic cores far exceeding Snoek's limit fabricated by simplified ferrite plating in open air

Iron spheres 2.0 /spl mu/m in diameter in distilled water was successfully encapsulated in dense Ni-Zn ferrite layer 15-20 nm thick by simplified ferrite plating method. In this method, a reaction solution of FeCl/sub 2/+NiCl/sub 2/+ZnCl/sub 2/ and a pH adjusting solution of KOH were added to the water. The solution was stirred at 25/spl deg/C in open air. The dissolved oxygen worked to oxidize a part of Fe/sup 2+/ to Fe/sup 3+/. The deposited Ni-Zn ferrite layer on Fe microsphere surface was composed of fine grains 10-15 nm in diameter. Since the Ni-Zn ferrite layer was very thin and dense, a large saturation magnetization M/sub s/=210 emu/g, almost the same as that of bare Fe, was obtained. The compacted cores of these Fe/ferrite microspheres exhibited excellent frequency characteristics exceeding Snoek's limit for Ni-Zn ferrite cores by factor 4.