Structure property relationship in longitudinal thin film magnetic recording media

The Co-based alloy/Cr layer structure has been the most widely used for magnetic hard disk media. Research has revealed that these magnetic properties are strong functions of film microstructure. Furthermore, the film microstructure can be engineered by varying the processing parameters. For this thesis, we have chosen to focus on microstructure, microchemistry, and their relation to magnetic properties. High spatial resolution characterization of the microstructure and microchemistry of computer hard disks, which is critical to understanding their structure-property-processing correlation, is possible by utilizing transmission electron microscopy (TEM), energy-filtered TEM (EFTEM), and nano-probe energy-dispersive x-ray spectroscopy (nano-probe EDS). Through the course of various studies, we were able to explore the effects of various hard disk processing parameters. For example, we determined the effect of substrate texture and microstructure on magnetic properties. We also studied the effects of sputtering temperature and magnetic alloy grain size on magnetic and recording properties. Throughout our studies, it was found that the influence of grain size appears to be quite important overall for increasing the coercivity of the hard disk media. Thus, we proposed to use a cumulative percentage plotting method which enables us to not only obtain average grain size but also visualize a whole grain size distribution handsomely, and find a corresponding mathematical formula for the distribution with minimal effort.; In addition to grain size and distribution, compositional segregation of non-magnetic materials was also studied. A series of CoCrPtTa, CoCrPtB 5, and CoCrPtB8 thin film longitudinal media were prepared under ostensibly identical sputtering conditions. High resolution TEM revealed that adding 5% or 8% boron to the magnetic layer resulted in significantly reduced average grain size compared to the media with a CoCrPtTa magnetic layer. It was also found that by adding boron, SNR and media noise properties were improved. While not affecting the lattice mismatch between the underlayer and the magnetic layer, the presence of B was found to enhance Cr segregation to cores as well as grain boundaries.