Material and recording properties of perpendicular CoCr media

Thin CoCr media for perpendicular magnetic recording were prepared on polyester substrates by RF sputtering. Both the volume coercivity and the surface coercivity show a strong dependence on substrate temperature and layer thickness, the surface coercivity being larger. The coercivities of layers deposited at substrate temperatures above and below 50°C show a totally different behaviour. These differences can be attributed to the microstructure. Small crystallites increase the coercivity, while the development of a columnar structure decreases the coercivity and increases the perpendicular anisotropy field. Recording experiments were performed using a ring head. The output for a layer with thickness d = 800 nm was found to be comparable with the output of longitudinal ME tape. At long wavelengths the output increases with increasing d. The recording density at which the output is half the maximum output is much smaller for thin longitudinal than for thicker perpendicular layers. The AC erased noise increases with d and the level is rather high. Both signal and noise are compared with theoretical models.