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Magnetically hard Sm2(Co0.8Fe0.2)17 and SmCo5 nanoparticles have been produced by using surfactant-assisted low- and high-energy ball milling techniques. Surfactants prevent the rewelding of the crashed particles during the milling process. Heptane was used as the milling medium and oleic acid as the surfactant. High-energy ball milling experiments took place in a milling vial with carbon steel balls by using an SPEX 8000M high-energy ball milling machine. The coercivity was found to increase with milling time with values of 2.3 kOe for Sm2(Co0.8Fe0.2)17 and 18.6 kOe for SmCo5 after 4 h of milling. Transmission electron microscopy data showed that the milled powders consisted of nanoparticles with an average size of 5–6 nm and a narrow size distribution. Samples deposited on copper coated carbon grid showed self-assembled nanoparticles which could be further aligned when subjected to a magnetic field.