High-Resolution Analytical TEM and Energy-Filtered Imaging of CoPt-Oxide Perpendicular Magnetic Recording Media

Abstract

Perpendicular magnetic media are expected to replace longitudinal hard-disk media in the near future, and to provide continued increases in areal density beyond the current maximum capacity of longitudinal media. High-resolution analytical electron microscopy is required for the study of these novel thin films because they comprise nanoscale grains and grain boundaries (often {approx}8 nm and {approx} 1 nm, respectively), and because the importance of examining the elemental distribution at near atomic level is paramount to understanding the magnetic performance. While perpendicular media offer many advantages, quantum-mechanical exchange coupling between grains is still problematic and requires the separation of grains similar to that required in longitudinal media. Energy-filtered TEM (EFTEM) imaging, which was used to examine compositional grain separation in longitudinal media, is capable of generating maps of the elemental distribution within the grains and the boundaries thereby depicting the extent of compositional separation. Combining EFTEM with other microanalytical techniques, such as high resolution TEM with energy-dispersive X-ray spectrometry, allows for both corroboration and easy quantification of individual grain and grain boundary areas. For this analytical TEM study, grain separation was attempted by generating non-magnetic oxygen-rich boundaries, either by flowing O{sub 2} gas during deposition or by sputtering a stablemore » oxide into the magnetic film. These CoPt-O and CoPt-oxide films were DC-magnetron sputtered at room temperature with increasing reactive O{sub 2} or oxide content. Magnetic properties were measured using a magneto-optical polar Kerr magnetometer. Both reactive O{sub 2} and oxide deposition methods, individually, increase grain separation and reduce intergranular exchange coupling, as shown by the hysteresis loop trends in Figures 1a and 2a. The difference between coercivity (Hc) and nucleation field (Hn) is a measure of the extent of exchange decoupling. The large increase in this loop shearing parameter as O{sub 2} or oxide content is increased is clear evidence of a corresponding decrease in exchange coupling.« less