Phase transitions and multidomain states in magnetic nanostructures with competing anisotropies

The evolution of the magnetic states in nanostructures with competing surface and bulk anisotropies was studied under a variation in the applied magnetic field. For spatially uniform magnetic states, the energy functional reduces to the energy of a bulk magnet in which the effective anisotropy depends on the thickness of the ferromagnetic layer. This dependence results in spin reorientation as the nanolayer thickness varies. The lines of first-order phase transitions and the equilibrium parameters of multidomain structures and domains of competing phases were determined. The calculated magnetic phase diagrams are used to analyze magnetic states and to construct magnetization curves.