Magnetic texturing of ferromagnetic thin films by sputtering induced ripple formation

Abstract

Ripple patterns created by sputter erosion of iron thin films induce a correlated magnetic texture of the surface near region. We investigated the magnetic anisotropy as a function of the residual film thickness and determined the thickness of the magnetically anisotropic layer as well as the magnitude of the magnetic anisotropy using by magneto-optical Kerr effect (MOKE) and Rutherford backscattering spectroscopy measurements. Ripple patterns were created by sputter erosion with 5keV Xe ions under grazing incidence of 80° with respect to the surface normal. For ion fluences of above 1×1016cm−2, the formation of ripples, with wavelengths between 30 and 80nm oriented parallel to the ion beam direction, is observed. MOKE measurements reveal a pronounced uniaxial magnetic anisotropy of the surface region of the films with orientation parallel to the ripple orientation and the ion beam direction. We find a layer thickness of 12±3nm, in accordance with the average grain size. The magnetic anisotropy within this layer varies from about 25% for thick residual films toward 100% for films with less than 30nm thickness. The magnitude of the magnetic anisotropy is determined by the shape anisotropy of the rippled surface as well as the interface roughness. We have demonstrated that sputter erosion yields highly anisotropic magnetic thin films and can be used to fabricate nanorods and nanowires with pronounced uniaxial magnetic anisotropy.