We investigate the influence of lateral variations of the second-order perpendicular anisotropy in thin films on the effective anisotropies required to represent this structure using a macrospin approximation. Second-order and fourth-order effective anisotropies are required for the macrospin approximation. In the case of quasistatic calculations, the fourth-order effective anisotropy is closely linked to deviations of the average magnetization angle from the field direction and lateral variations of the magnetization direction in the structure leading to dependence on the field strength and the lateral length scale of anisotropy variations of the effective anisotropies. We find that the field and lateral length-scale dependence of the effective anisotropies extracted from simulations of the magnetization dynamics are profoundly different from those of the quasistatic simulations. This is caused by resonance localization that depends on the orientation of the external magnetic field.

We report on the results of first principles calculations investigating the influences of Mn doping on the local moments and stacking fault energies (SFEs) in the Co${}_{95.8}$Mn${}_{4.2}$ and Co${}_{91.6}$Mn${}_{8.4}$ systems as compared to pure face-centered cubic Co. A supercell was developed to maintain periodicity in calculations, provide a simple relaxation mechanism, and allow for easy expansion to accommodate different concentrations of Mn. Calculations to determine the generalized SFE were performed on relaxed and non-relaxed systems in both ferromagnetic and nonmagnetic states. Analysis revealed fluctuations in the magnetic moments that are closely tied to the relaxation state and faulting state of the system. In the case of systems containing Mn, we observed a dependence of the SFE on the location of the Mn atom(s) within the supercell relative to the stacking fault interface and a strong induced magnetic moment for these atoms.