Formation Energy of Superlattice in Ni₃Fe (II)

Kinetics of the Superlattice in the Stage of Local Ordering

Abstract

The change of the internal energy of Ni₃Fe superlattice during cooling processes was studied by specific heat measurement for various rates of cooling. After eliminating the part of the internal energy due to magnetic transformation, it was shown that the formation of local order starts already at 600°C on cooling, and its rate attains a maximum at 520°C, decreasing to zero at about 400°C. The specific heat curves on cooling do not show any anomaly at 500°C, which is critical temperature for the long range order. The formation rate of local order at steady temperature annealing was also studied by keeping the specimen at 510°C and observing the heat of evolution directly. It was confirmed that the rate of local order formation is large enough to be observed at this temperature. It decreases monotonously and becomes zero after about five hours annealing. These data are all consistent with our previous assumption that one of the two steps’ precesses of the formation of superlattice in Ni₃Fe at 490°C is the development of local order which has no critical temperature.