Magnetic domains in epitaxial BaFe₁₂O₁₉ thin films with perpendicular anisotropy

Magnetic domains, microstructure and magnetic properties of highly oriented barium ferrite thin films with perpendicular anisotropy have been investigated with magnetic force microscopy (MFM), VSM, SEM and TEM. Two kinds of magnetic domain are energetically favourable: (a) cluster-like structure in as-deposited films grown at 770 .C; (b) stripe domains in layers annealed at high temperature (900 .C). Such a difference in domain configuration can be related to microstructure. Small single-domain grains (70 nm) exist in as-deposited films whereas annealed films consist of large multidomain platelets. The magnetic measurements (hysteresis loops and virgin curves) reveal that magnetization reverses by rotation and wall motion for cluster-like and stripe domains respectively. A good agreement was established between the domain width measured by MFM and that predicted by using the Kooy-Enz model (Kooy C and Enz U 1960 Philips Res. Rep. 15 7) in our stripe structure. The analyses of minor loops and virgin curves suggest that the coercivity in stripe domains is controlled by wall nucleation rather than pinning.