Domain wall pinning transition in an iron-rich FeCu alloy

Abstract

Specimens of α-phase solid solution of iron-rich FeCu(1.07 at. % Cu) were thermally aged at 700 °C for different time durations. Precipitation and growth of εCu took place during the heat treatments. The specimens were polished and were examined with a transmission electron microscope. The size, density, and shape of the precipitates were determined for different aging conditions. These parameters were fit into the strong and weak domain wall pinning models, allowing values of the coercive field Hc to be predicted. Comparison between the predicted and measured coercive fields shows that weak pinning theory agrees with the observed Hc in low age specimens. For specimens aged over 1700 min, strong pinning theory can provide acceptable calculated Hc values. The pinning index β′ related to the ratio of the domain wall area per pin in the static and dynamic states is also calculated for each specimens. β′ values in low age specimens are found to be <1, which indicates weak pinning. For prolonged age specimens, β′ values are close to or larger than 1, and strong pinning is indicated.