Micromagnetic finite element calculations describe the interactive mag
netisation processes which determine the magnetic properties of rare-e
arth-based composite magnets and Co/Pt multilayer structures. Sm2F17Nx
-based composite magnets show better temperature stability than Nd2Fe1
4B-based magnets. In Co/Pt multilayers spatial fluctuations of the mag
netocrystalline anisotropy energy create barriers for domain wall moti
on. The pinning field of domains increases with increasing grain size.