Abstract Magnetizations at applied fields up to 120 kOe and electronic specific heats have been determined for ternaries represented by the formula Y 6(Fe 1− x Mn x ) 23. The Curie temperature and ordered magnetic moment of Y6Mn 23 and Y 6Fe 23 decrease sharply when these materials are formed into solid solutions, being minimal in the vicinity of the equimolal solution. To test whether the reduction is a band effect electronic specific heats were measured; they are maximal where T c and the moment are minimal, indicating unimportance of band effects. Curie-Weiss behavior is exhibited at low fields, suggesting rather localized d-electrons. The nearest neighbor distances are such as to lead to antiferromagnetic Mn-Mn interactions. Y 6Mn 23 is taken to be ferrimagnetic whereas Y 6Fe 23 appears to be ferromagnetic. While the magnetic structure of the ternaries is yet to be fully clarified, it is clear that antiferromagnetic exchange is enhanced when either binary is formed into a ternary. It also appears that the Mn-Fe coupling is antiferromagnetic in the ternaries.