Effects of microstructure and crystallography on the magnetic properties of recording media

The recording performance of sputtered thin-film longitudinal magnetic media is determined primarily by the magnetic cobalt alloy microstructure, which is in turn controlled by the chromium underlayer microstructure. Optimization of magnetic properties requires nanoscale characterization throughout the depth of these layers. The unique characterization capabilities of transmission electron microscopy (TEM) are essential to this analysis. However, the magnetic recording industry has largely ignored TEM because of difficulties in sample preparation and analysis.; This thesis studies the relationships between processing of the sputtered thin-films, resulting microstructures and ensuing performance of recording media. Magnetic property measurements including coercive field, squareness, magnetic anisotropy and media noise are related to deposition parameters such as substrate temperature and sputtering gas pressure. This is achieved by simultaneously understanding the microstructural effects of changing each sputtering parameter and the relationship between microstructures and resulting magnetic properties. It will also be shown that careful TEM analysis can overcome previous difficulties, and is indispensible to characterization and development of recording media.; High adatom mobility Cr deposition produces a columnar microstructure with 500A grains having {dollar}langle 200rangle{dollar} axes normal to the local substrate surface. Low mobility gives less oriented 500A columnar grains and smaller physically separated growth columns.; High mobility Co alloy growth conditions can result in a coherent Co alloy/Cr interface, with hcp Co alloy basal planes parallel to bcc Cr {dollar}{lcub}110{rcub}{dollar} planes and the Co alloy {dollar}langle 11bar{lcub}2{rcub}0rangle{dollar} axis normal to the local substrate surface. The magnetically easy c-axis then lies nearly in the film plane, with out-of-plane component dependent on local substrate surface roughness. Anisotropic substrate roughness, induced for tribologlcal reasons, produces anisotropy in the c-axis out-of-plane component, resulting in anisotropic magnetic properties.; Low mobility Co alloy deposition results in poor interface coherence and little preferred c-axis orientation, resulting in lower coercivities, but produces a separated microstructure that lowers media noise. Both in-plane c-axis orientation and grain separation are obtainable in a CoCrTa alloy. This medium has high coercivity, and lower noise than similarly processed CoCrPt and CoNiCrPt media that do not show grain separation.