Crystallographic orientation of textured CoCrTa/Cr sputtered thin film media for longitudinal recording

Abstract

We have studied the influence of deposition conditions on the structure and properties of Co84Cr14Ta2 alloy magnetic thin films and Cr underlayers sputtered onto circumferentially textured and smooth polished NiP/Al substrates. Suitable processing conditions provide in-plane magnetic anisotropy in the textured media, with enhanced coercivity (Hc) and coercivity squareness (S*) in the circumferential direction and reduced Hc and S* in the radial direction. The crystallography in these films was studied by transmission electron microscopy (TEM) to address the origin of the observed magnetic anisotropy. The CoCrTa alloy grains are found to grow semicoherently on the chromium underlayer, resulting in vertical <200≳ Cr and <112̄0≳ CoCrTa axes. This requires an in-plane orientation of the CoCrTa c axis, which is observed to be nearly random by high-resolution TEM. Microdiffraction shows apparent preferred c-axis alignment locally at texture lines, but this observation is primarily attributable to asymmetric tilting of the vertical growth direction caused by the substrate topography. The <112̄0≳ growth axis appears to be perpendicular to the local grooved surface, not the bulk surface, requiring a local c-axis out-of-plane tilt near the grooves. The anisotropic surface topography induces a corresponding anisotropy in the out-of-plane component of the magnetically easy c axis in the CoCrTa alloy, which we suggest has implications on the bulk magnetic anisotropy in such films.