Ion induced nanoscale surface ripples on ferromagnetic films with correlated magnetic texture

We have investigated the correlation between nanoscale surface ripple patterns and the magnetic texture of polycrystalline iron and nickel thin films. The ripple patterns were created by ion beam sputter erosion of films evaporated on Si substrates with 5 keV Xe ions under grazing incidence and fluences between 1015 and 1017 cm−2. The as-deposited films with an rms roughness of about 1 nm are magnetically isotropic. Sputter erosion reduced the coercive field of the films for all erosion conditions investigated. Sputter erosion at an incidence angle of 80◦ with respect to the surface normal produces rather smooth films and for ion fluences exceeding 1 × 10 cm−2 formation of ripples parallel to the ion beam direction with wavelength between 30 and 80 nm is observed. Magnetooptical Kerr effect (MOKE) measurements reveal a pronounced uniaxial magnetic anisotropy of the only 1–2 nm thin irradiated surface region of the films with orientation parallel to the ripple orientation and also parallel to the ion beam direction. Almost complete sputter erosion of Fe films resulted in the formation of Fe nanorods oriented parallel to the ion beam direction with 100% uniaxial magnetic texture. 3 Author to whom any correspondence should be addressed. New Journal of Physics 9 (2007) 29 PII: S1367-2630(07)30733-7 1367-2630/07/010029+12$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft 2 Institute of Physics DEUTSCHE PHYSIKALISCHE GESELLSCHAFT