Highly Oriented High-$B_s$Fe-Co Soft Underlayer for High-Density Perpendicular Recording Media

Two types of media with a high-B
_s
Fe-Co soft underlayer (SUL) were prepared to reduce the film thicknesses of the Ru intermediate layer and the SUL. The crystal orientation of the media was greatly changed by using a thin Ta underlayer. The magnetic properties of the SULs were similar, independent of the existence of the Ta underlayer. However, the media with high orientation have large H
_c
and squareness ratio. The Ru layer thickness for obtaining the maximum H
_c
and squareness ratio is 5-7 nm. This seems to be due to the imperfection of Ru orientation. From the read-write properties, the minimum of the Ru layer thickness is 7 nm. However, from vibrating-sample magnetometer measurements, the magnetic interaction between the recording layer and the Fe-Co SUL is broken by using an Ru layer of 1-3 nm. The intermediate layer thickness could be reduced down to about 1 nm if the orientation is improved