Alloy nanoparticles in the Mn-Al system were prepared by the plasma arc discharge method. The influence of process parameters on the vaporization rate, composition, particle size, and magnetic properties of the as-produced nanoparticles was investigated. The Mn content was found to be higher in the nanoparticles than in the corresponding mother alloy, although the difference diminished with the reaction time. With increasing H(2) content in the reaction gas, both vaporization rate and particle size increased. With 30 at.% Mn, the average particle diameter in pure Ar was 35.2 nm, whereas that in an atmosphere with Ar:H(2) = 60:40 was 95.4 nm. With the addition of a small amount of carbon, epsilon-phase nanoparticles were synthesized. After heat treatment in a vacuum for 30 min at 400-600 degrees C, the nonmagnetic epsilon-phase was transformed into the ferromagnetic tau-phase and a very high coercivity of about 446 kA/m was achieved. (C) 2010 Elsevier B.V. All rights reserved.