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PbySn1-x-yMnxTe in various compositions, including Sn1-xMnxTe, displays an intriguing phase diagram which includes the carrier concentration p as an important parameter. A ferromagnetic state was found to exist only above a critical concentration pc3×1020 cm−3 at which a heavy hole band will be filled and starts to contribute to the RKKY interaction between the Mn ions.1 The present contribution deals with the magnetic phase diagram for low Mn concentrations (cᶱ2-3 K), for p exceeding pc. However, for extremely high carrier densities, p 1021 cm−3, the data show a substantial deviation from what is commonly observed. This is characterized by a significant drop of Tc well below ᶱ and a rather broad maximum in the specific heat. Tentatively this transformation at higher p might be attributed to a ferromagnetic (F) to spin glass like transition, which, qualitatively, is in harmony with the competitive balance between ferro and antiferromagnetic (AF) exchange characteristic for the simple RKKY interaction: an increasing wave number (p1/3) will increase the number of antiferromagnetically long range coupled ions, at the expense of the strong ferromagnetic coupling between Mn2+ at shorter distances. Moreover, the mean distance between the Mn ions for x=0.02 is such that this delicate interplay between F and AF coupling should be observable.