Comparative view of coercivity mechanisms in soft and hard magnetic materials

The main differences between soft and hard magnetic materials are commented on. It is discussed how the coercivity mechanisms can be affected by the domain wall energy. A spherical cap nucleus is used for this analysis. There is a competition between magnetostatic energy and domain wall energy terms. As a consequence, for soft magnetic materials, the magnetostatic energy term is dominant over the domain wall energy term. An explanation for the dependence of the coercivity with grain size is presented. For grain size above the single domain size, in hard magnetic materials with high magnetocrystalline anisotropy, the coercivity decreases following a law proportional to the inverse of the square root of the grain size, whereas in soft magnetic materials, the coercivity reduces proportionally to the inverse of grain size.