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Magnetic particles with high permeabilities and moments, and low losses, have considerable potential for high-frequency power applications. In this paper, we report on spherical Co50Fe50 fine particles prepared by spark erosion in liquid argon and nitrogen, kerosene, ethanol, and water. X-ray and Mössbauer spectra showed that the as-sparked Co50Fe50 particles made in liquid argon and nitrogen exhibited primarily a disordered α-FeCo structure, which became mostly ordered B2 structure after annealing at 525°C for 2 h. The as-sparked particles prepared in liquid kerosene and ethanol consisted of the disordered α-FeCo structure and various iron carbides. Annealing removed X-ray and Mössbauer evidence of carbides, and the particles then exhibited only the ordered B2 structure. As-sparked particles made in water contained both the α-FeCo disordered phase and an (FeCo)O phase. After annealing, only ordered B2 and Fe3O4 phases were found in these particles. The room-temperature magnetic moments and coercivity for the annealed particles were also measured. The complex magnetic permeability measured at 30 MHz indicated that the smaller particles generally exhibited relatively larger real permeability, μ', and smaller imaginary component, μ'', than the larger particles. Relatively large μ' and small μ'' (i.e., losses), were found for the as-sparked particles made in water.