Magnetic Anisotropy of FeCo Films Induced by Obliquely Sputtered Ru Underlayers

The magnetic properties of Si/Ru(t nm)/Fe
₉₀
Co
₁₀
(3.0 nm)/Ru (4.0 nm) films with obliquely sputtered Ru underlayers were studied as a function of Ru underlayer thickness (t). It was found that an obliquely sputtered Ru underlayer produces high uniaxial anisotropy in the Fe
₉₀
Co
₁₀
layer with extremely small hysteresis in the hard axis direction. The anisotropy field can be increased by increasing Ru underlayer thickness. X-ray reflectometry showed that the interfaces of the samples were quite smooth with rms roughness as small as 0.35 nm. The high uniaxial anisotropy of the samples shows high thermal stability and endures e-beam lithography for microscopic device fabrication. We discuss the origin of this high anisotropy in terms of a magnetostatic effect arising from an anisotropic surface morphology.