Domain-wall pinning and nucleation in SmCo5 sintered magnet alloys

The coercive field, H 0, is calculated for SmCo5 alloys containing planar pinning sites of Sm2Co17. In a reverse field H < H 0 the 360° pinned double wall cannot escape and split into two 180° walls unless an activation energy is supplied. The value of the activation energy is calculated and found to be proportional to (1 – H/H 0)3/2. This result allows the pinning to be identified with a simple phenomenological model characterized by a force constant F and a range constant b. The double wall can then be treated as a membrane, of position independent wall energy Γ, subject to field and interaction forces. Thermal activation may supply enough energy to form blisters on the walls, allowing them to escape from the continuous lamellar pins in coercive fields H c < H 0. The predicted values of H c at temperatures from 4.2 to 500 K are compared with experimental data and give reasonable agreement with experiment for Sm2Co17 lamellae of 50–100 Å thickness.