Effect of top Ru deposition pressure on magnetic and microstructural properties of CoCrPt–SiO2 media in two-step Ru layer

Two-step-deposited Ru layers of 20 nm have been employed as an underlayer for CoCrPt–SiO2 perpendicular magnetic recording media. The bottom Ru layer of 10 nm is deposited at 3 mTorr for good texture of hcp (0002) and the top Ru layer of 10 nm is deposited at various conditions. Sputtering power and Ar pressure are variables for the top Ru layer deposition. As the sputtering pressure of the top Ru layer increases, coercivity (Hc) of the CoCrPt–SiO2 layer increases and then saturates or slightly decreases with a further increase of sputter pressure. The Hc increase is mainly due to exchange decoupling among grains of CoCrPt. The c-axis alignment of the Ru layer by the two-step deposition method is much improved compared to that of a single-step-deposited Ru layer when the sputtering pressure is higher than 3 mTorr. The grain size of Ru layer is smaller and the grains are well separated by void boundaries when the top Ru sputtering pressure is high. There is a one-to-one relationship between small Ru grains and CoCrPt grains. Although the grain size of CoCrPt layer is small with a good c-axis alignment in the case of lower-pressure-deposited top Ru underlayer, Hc is small. The reason will be discussed in terms of grain interconnection.