Dependence of thin-film media microstructure and recording properties on composition of very thin Cr-based seedlayers

WCr_100-X (X=0-100) and CrTi₁₅ seedlayers with a thickness of 0.5 nm have been utilized to reduce the grain size of CoCrPtB-CrMo longitudinal media. It is found that grain size and media noise are reduced when using WCr_100-X (X=0, 25, 50) seedlayers, but not reduced with CrTi₁₅ or WCr_100-X (X=75, 100). Auger electron spectroscopy (AES) analysis results show that the critical thickness just before the W, WCr₅₀ and Cr seedlayers become continuous are 1.5, 2.5, and 5 nm, respectively. Reflection high-energy electron diffraction (RHEED) analysis shows that the structure of a 2.0-nm W film consists of very small two-dimensional randomly oriented crystal grains. This result suggests that the W seedlayer, which has the highest melting point, forms a layer-like film with very small and dense island grains, due to its high free surface energy and low mobility. On the other hand, WCr₅₀ and Cr seedlayers, which have a lower melting point, form island films. It is concluded that WCr_100-X (X=0, 25, 50) seedlayers effectively reduce the grain size and media noise in CoCrPtB-CrMo media.