Pinning theory of domain walls in helical magnets

The theory of elasticity and pinning of domain walls in helical magnets is presented. Domain walls perpendicular to the helical axis show non-local elasticity and are marginally pinned by local disorder. Weak anisotropy combined with magnetic dilution leads however to a non-local bulk pinning effect. Domain walls with other orientations include generically vortex arrays, similar to type-II superconductors. Their pinning force is calculated as a function of wall orientation, pitch angle and impurity concentration. It is shown that metastable domains can vary between needle and pancake like shape.