Experimental studies of phase equilibria in the Co-Mn-C system and construction of the system melting diagram at atmospheric pressure have allowed a comprehensive investigation of capillary phenomena at the Go-Mn growth medium-carbon material interface that occur due to variations of both the liquid phase composition and melting temperature (along the solid-liquid equilibrium line). It was shown that cobalt melts containing 10-14 at.% Mn might be recommended as growth media for diamond synthesis. Along with the relatively low p,T-parameters, the introduction of manganese in such quantities provides optimal synthesis conditions, i.e., the lowest energy at the crystal -growth medium interface with a rather high solubility of carbon in the melt. (C) 1998 Elsevier Science B.V. All rights reserved.