Coercivity-gradient bi-layered thin-film media for longitudinal recording

A new coercivity-structure was proposed, and a new process technique was developed for controlling the Hc of second and subsequent magnetic-layers in multi-layer media. A narrow slit cathode was used to sputter Cr-interlayer. Conventional and new Hc-gradient CoCrTa-bi-layer media were sputtered by varying Cr-interlayer thickness 0-25 Å with fixed Cr-underlayer and magnetic layers. In one case, to achieve higher Hc for the top-magnetic layer, Hc gradient bilayer media of Mrt:3.6 memu/cm² were sputtered by using 250 V DC-bias during second magnetic-layer deposition which produced about 300 Oe higher Hc for the top-layer. The bi-layer media reduced media-noise about 30% and increased SNR about 5 dB in comparison to mono-layer media at 66.3 KFCI recording-density. However, conventional bi-layer media produced about 6-7 dB lower overwrite (OW) in comparison to mono-layer media, whereas the new Hc-gradient bi-layer media with higher Hc showed about 5 dB higher OW and 5-12% higher HF-amplitude in comparison to conventional bi-layer media