Structural, magnetic and recording properties of Co-Cr layers for perpendicular recording using Ge nucleation layers

The influence of amorphous Ge underlayers on the structural, magnetic, and recording properties of Co-Cr recording media was studied. The media were prepared by RF sputtering on PET (polyethylene terephthalate) substrates just above room temperature. The Ge underlayer is observed to promote the perpendicular anisotropy of the Co-Cr, provided the Ge-layer thickness exceeds a critical value of about 200 nm to effectively seal the PET substrate. The resulting films also show low coercivity (10 to 30 kA/m), a columnar structure (column width 30 to 50 nm), and signal and noise features as described earlier for media, deposited at low temperature directly on the PET substrate. From the slope of the perpendicular hysteresis loop, the maximum in the noise spectrum, the noise periodicity and erasure experiments the medium domain period is estimated to be 370 to 780 nm for a 600 nm thick Co-Cr layer. These domain periods are consistent with a continuous perpendicular film model of the medium.