Effective anisotropies in magnetic nanowires using the torque method

The effective anisotropy of Co-based nanowires such as CoFe, monocrystalline hcp Co and polycrystalline Co with a mixture of fcc and hcp grains has been evaluated through micromagnetic modeling based on the magnetization torque simulations. We retrieve the experimental profile of the torque curves and show that the non-harmonic forms observed at low fields correspond to the presence of open vortices at the nanowire ends. Our results show that strong hcp anisotropy of Co cannot overcome the uniaxial character of the effective anisotropy which always remains parallel to the nanowire axis, even in the case of magnetocrystalline easy axis perpendicular to the nanowire. We evaluate effective anisotropy values for monocrystalline Co nanowires with different easy axis orientations and polycrystalline Co nanowires with different mixtures of hcp and fcc grains.