“…To overcome this shortcoming, an effective approach is to disperse magnetic metallic particles with size less than the skin depth in insulator matrix. Various material systems (e.g., ␣-Fe/Fe 3 B/Y 2 O 3 [3], Fe/SiO 2 [4], Co/SiO 2 [5], Co/PVP [6], Co x Ni (100−x) /MnO 2 [7,8], Ni/C [9]) have been attempted. The electrical resistivity of these systems can be enhanced by several orders and reach 10 4 cm [3]; and the eddy current effect can be suppressed effectively due to the presence of the insulator matrix.…”