Mechanochemical processing has been used for producing ultrafine magnetic metal powders, including Co and Ni. Uniform particle sizes of 10-20 nm were obtained by the chemical reduction of cobalt and nickel chlorides during mechanical milling with Na. The occurrence of combustion during milling was prevented by the addition of excess of NaCl as a diluent. The ultrafine particles were characterized by saturation magnetization values 90-95% of their respective bulk values and significantly increased coercivities.
Ding, J., Tsuzuki, T., Mccormick, P., & Street, R. (1996). Ultrafine Co and Ni Particles Prepared by Mechanochemical Processing. Journal of Physics D-Applied Physics, 29, 2365-2369. https://doi.org/10.1088/0022-3727/29/9/020