Domain wall pinning at random inhomogeneities

A new statistical theory of domain wall pinning by a random array of inhomogeneities is outlined. Each pin site is characterized by its maximum pinning force f. The critical field H
o
required to unpin a 180° wall, in the absence of thermal activation, is found to be proportional to f
²
ρ/γ where ρ is the volume density of pins and γ is the domain wall energy. In an applied field H < H
o
the wall can be unpinned if an activation energy E is supplied thermally. Expressions for this energy are given for strong and weak pinning régimes. The use of these equations in interpreting the observed temperature dependence of coercive forces and magnetic viscosity results is discussed.