Kinetics of coercive force changes during aging of Co‐Fe‐Cu‐Ce permanent magnets

The intrinsic coercive force iHc of age‐hardening Co‐Fe‐Cu‐Ce permanent magnet alloys has been studied as a function of aging time at temperatures between 375 and 600 °C following solution treatment at 1000 °C. A new aging peak at ∠500 °C has been observed in addition to that previously observed at ∠400 °C. This new peak occurs at shorter times (20 mins. vs. 17 h) and the maximum iHc obtainable is smaller than that obtained after aging at 400 °C. It is absent in Ce‐rich alloys, but persists and broadens to higher temperatures in Ce‐poor alloys. The activation energy for the aging process in ∠30 kcal/mole for both peaks. The results are interpreted in terms of eutectoidal decomposition for the alloys.