The rotational limit line was introduced to the rotational hardening law and a parameter b was added to the model to reflect the evolution of anisotropy.

To take an extreme example, imagine that an electron does not scatter in an iron layer unless its spin points in the same direction as the layer's magnetization.

With these equations, they have investigated the problem of Faraday rotation in a longitudinally magnetized ferrite rod with tapering cross-sections at both ends.