Co/Pt superlattices with ultra-thin Ta seed layer on NiFe underlayer for double-layer perpendicular magnetic recording media

Co/Pt superlattices with an ultra-thin amorphous Ta seed layer on a Ni₄₅Fe₅₅ underlayer were fabricated for double-layer perpendicular magnetic recording media using a special hard disk sputtering system with a triple-target DC magnetron cathode (Triatron). A 2.5 nm thick Ta seed layer was found to improve the crystalline structure and increase the coercivity of the Co/Pt superlattices from 1.13 to 2.17 kOe. A 2.5 nm Ta layer on a 200 nm thick magnetically soft NiFe underlayer was found to further increase the coercivity from 2.25 to 5 kOe. In addition, the sheared slope of the sides of hysteresis loop of Co/Pt superlattices was significantly improved from about 5 Gauss/Oe (with only a 2.5 nm Ta seed layer) to about 1.1 Gauss/Oe (with both a 2.5 nm Ta seed layer and a 200 nm NiFe underlayer)