AFM STRUCTURE AND MEDIA NOISE OF SMCO CR THIN-FILMS AND HARD DISKS/

Longitudinal media for ultrahigh density recording require a high coer civity and a low medium noise. While the coercivity is controlled main ly by the chemical composition of the alloy, the medium noise is influ enced significantly by the microstructure of the underlayer. We used a tomic force microscopy (AFM) to study the microstructure of Cr underla yers and SmCo magnetic films. The AFM study shows that the Cr grains h ave elongated ''rice''-like granular features whereas the SmCo grains without an underlayer appear circular with nonuniform grain size. The Cr underlayer grows as well isolated columns with voids. When thin SmC o films (<20 nm) were deposited on the thin Cr (<35 nm) underlayers th e SmCo grains were found to replicate the isolated, columnar structure of the underlayer. The intergranular exchange interaction and the rec ording media noise of SmCo/Cr thin films decreased with a decreasing t hickness of the Cr underlayer. The medium noise of high coercivity SmC o/Cr hard disks prepared on thin Cr underlayers remained almost flat w ith no supralinear increase when tested up to 2760 fc/mm (70 kfci).