Role of atomic mobility in the transition noise of longitudinal media

The relationship between grain growth morphology and the transition noise of high-density CoPtCr media on Cr underlayers is examined. The growth morphology is shown to depend on the sputtering pressure, substrate bias, and substrate temperature. Development of isolated magnetic grains is promoted when the mobility of the sputtered atoms is reduced, i.e. at high sputtering pressure, low substrate temperature, and no substrate bias. As the magnetic grains become more isolated, the media transition noise is significantly reduced, accompanied by a simultaneous reduction in the coercive squareness. This indicates that the transition noise is primarily governed by the intergranular exchange coupling among the magnetic grains, which can be optimized by controlling the grain growth morphology. The microstructural features of the decoupled media correspond to the zone I structure in J.A. Thornton´s (1986) microstructure zone diagram