Ion irradiation driven changes of magnetic anisotropy in ultrathin Co films sandwiched between Au or Pt covers

Modifications of magnetic anisotropy of 30 keV Ga⁺ ion irradiated ultrathin Co films sandwiched between Au or Pt buffer and capping layers are investigated as a function of magnetic layer thickness, d_Co, and the ion fluence, F. Maps (d_Co, F) of saturation fields have been derived from local magnetooptical polar Kerr effect (PMOKE) measurements. The areas with increased remanent magnetization and/or saturation fields, which are directly related to the uniaxial anisotropy, adopt linear shapes for the two branches in the maps. They are very distinct, especially for the Pt/Co/Pt system irradiated at lower and higher fluence. Replacement of Pt with Au in the buffer layer results in minor influence on the magnetization properties of the irradiated trilayers. Au as a capping layer significantly decreases the anisotropy in the branch appearing at lower fluence. In the Au/Pt/Au sandwich, a severe reduction of induced anisotropy is observed in both branches. The proposed phenomenological model describing experimentally investigated magnetic anisotropies enables separation of surface and volume contributions to both branches of enhanced anisotropy.