The effects of B2 structured underlayers on thin film magnetic recording media

Abstract

It is well known that underlayers have profound effects on the magnetic properties of longitudinal thin film media. These effects are derived from the underlayer's influence on the structural features of the magnetic media such as crystallographic texture, grain size and grain isolation. Pure Cr has been the most popular underlayer for Co alloy thin films for more than two decades mainly because Cr underlayers can enhance the c-axis in-plane crystallographic texture of the overlying Co alloy thin films. Many investigators have studied alternative underlayers and have achieved various degrees of success. However, those underlayers are seldom different from the BCC structure or are Cr with various alloying additions. We have studied NiAl and FeAl underlayers with the B2 ordered structure (CsCl prototype) which have lattice constants similar to that of Cr. Rf diode sputter deposited NiAl and FeAl films were found to have the B2 structure and have a smaller grain size and more uniform equiaxed grains compared to that of a similarly deposited Cr film. X-ray diffractometry studies showed that CoCrPt films grown on NiAl or FeAl underlayers tend to have the (101̄0) crystallographic texture with a better in-plane c-axis orientation than CoCrPt films grown on Cr underlayers. The in-plane coercivities of the CoCrPt/NiAl and CoCrPt/FeAl films can be significantly improved by inserting a thin intermediate layer of Cr between the CoCrPt and its underlayer. Cr, NiAl and FeAl underlayers are found to have a strong (002) crystallographic texture when sputter deposited MgO seed layers are used. The MgO seed layers increase the coercivities of the CoCrPt films having Cr or NiAl underlayers but decrease the coercivities of the CoCrPt films having FeAl underlayers.