Magnetic configurations of Co(111) nanostripes with competing shape and crystalline anisotropies

Nanostripes with varying widths are lithographed on Co thin films with strong magnetic anisotropy resulting from the epitaxial growth onto vicinal Si(111) substrate. The competition between magnetocrystalline and shape anisotropies is used to tune the magnetic behavior of Co nanostripes. Single domain configuration is observed for nanostructures where magnetocrystalline and shape anisotropies go along the same direction. However, more complicated configurations such as open stripe domains can be developed when both anisotropies compete. The nanostructures have been experimentally characterized by longitudinal magneto-optical Kerr effect and magnetic force microscopy (MFM). Micromagnetic simulations performed by finite-element and finite difference codes are in good agreement with the experimental results. The use of MFM based techniques such as the variable field magnetic force microscopy and the so-called three-dimensional modes has allowed us to follow the evolution of the domains and domain walls under externally applied magnetic fields, i.e., to deeply understand the magnetization reversal process in the multidomain nanostripes. In particular, the nanostripes with competing anisotropies and a high aspect ratio present vortex configuration along the domain walls which have a key role in the magnetization reversal process.The authors acknowledge the financial support from the Spanish Ministry of Economy and Competitivity under Projects No. CSD2010-00024, No. FIS2010-20979-C02-02, and No. MAT2010-20798-C05-01, and Fellowship No. SB2010-0123, provided to. Y. Ivanov as well as the financial support from the regional Government of Madrid under Project No. S2009MAT-1467