Chromium segregation in CoCrTa/Cr and CoCrPt/Cr thin films for longitudinal recording media

Analytical electron microscopy is employed to correlate Cr segregation in Co84Cr12Ta4/CT and Co76Cr12Pt12/Cr films with specific microstructural features such as grain boundary mis-orientation. Energy-filtered (EFTEM) chemical maps show that Cr segregation occurs independently of the Cr underlayer, and is highly alloy dependent. The CoCrTa film contained extensive grain boundary Cr enrichment whereas EFTEM images from the CoCrPt media show homogeneous Cr distribution. No statistically significant Ta or Pt segregation was observed. EFTEM elemental maps and energy dipersive spectroscopy (EDS) indicate that grain boundary Cr segregation depends on the type of boundary. Quantitative analysis of the Cr levels using nanoprobe EDS shows that the random angle grain boundaries contain more Cr (23 +/-4 at%) than 900 boundaries (17 +/-4 at%). EDS and EFTEM composition profiles show Cr enriched grain boundaries surrounded by regions of Cr depletion.