Influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films

Using a combination of resonant soft x-ray scattering, magnetometry, x-ray reflectivity, and microscopy techniques we have investigated the magnetic properties and microstructure of a series of perpendicular anisotropy Co/Pt multilayer films with respect to structural disorder tuned by varying the sputtering deposition pressure. The observed magnetic changes in domain size, shape, and correlation length originate from structural and chemical variations in the samples, such as chemical segregation and grain formation as well as roughness at the surface and interfaces, which are all impacted by the deposition pressure. All samples exhibited short-range "liquid-like" positional ordering over significant portions of their major hysteresis loops, while only the lowest disorder samples showed evidence of a random "gas-like" distribution of magnetic domains, present just after nucleation as well as prior to saturation. The structural and chemical disorder induced by the higher deposition pressure first leads to an increase in the number of magnetic point defects that limit free domain wall propagation. Then, as the sputtering pressure is further increased, the domain wall energy density is lowered due to the formation of local regions with reduced magnetic moment, and finally magnetically void regions appear that confine the magnetic domains and clusters, similar to segregated granular magnetic recording media.