Shape Anisotropy as Coercivity Mechanism

Abstract

The Alnico magnets (also called Ticonal) have coercivity attributed to shape anisotropy. The conditions for appearing this type of anisotropy are discussed, and the principal is the existence of elongated grains parallel to the easy magnetization axis. A very important detail is that the conditions assumed in the Stoner Wohlfarth model have to be obeyed. The assumptions are i) ferromagnetic phase with single domain particle size and ii) grains without magnetic interaction between them, magnetically insulated by a grain boundary paramagnetic phase. In Alnico magnets, the coercivity mechanism is coherent rotation of single domain size particles.