Granular inclusions, grain boundaries, lamellar precipitates, and the crystalline surface have been examined as possible nucleation centers for domains of reverse magnetization in ferromagnetic materials. It is concluded that the surface density of magnetic poles at the grain boundaries ${\omega }^{*}$ is the most common source of nucleation energy in polycrystalline materials.

The concept of nucleation of domains of reverse magnetization has led to a calculation of three more terms which may contribute to the coercive force in polycrystalline materials, viz., a grain-boundary, a lamellar-precipitate, and a domain-wall-surface-tension contribution.

The theoretical predictions are compared with several old experiments. New insight is gained on the problem of stress sensitivity of polycrystalline ferromagnetics and $B-H$ loop shape.

• Received 17 December 1953

DOI:https://doi.org/10.1103/PhysRev.95.917