The Heat Capacities of Some Copper-Manganese Alloys

The anomalous behaviour of the heat capacities at the Néel points of copper-manganese alloys containing 80 and 85 at.% Mn is more marked than that observed in other metallic antiferromagnetics. The entropies associated with the anomalies are 0.20 and 0.35 cal mol -1 deg -1 , respectively, and are significantly less than the value R ln (2 S +1) predicted by localized theories of antiferromagnetism. It is concluded that these results indicate that the appropriate model of antiferromagnetism in metals is not one based on completely localized moments.