Structural and magnetic characterization of longitudinal recording media

Cobalt alloy films are used extensively in high-density magnetic recording media, where the microstructure plays a critical role in the recording performance. Circumferential grooves polished into the Al/NiP substrate cause a magnetic anisotropy, referred to as “orientation ratio,” (OR), to develop. OR is defined as the ratio of coercivities parallel and perpendicular to the grooves. This thesis investigates the microstructural origins of OR and their impact on the magnetic anisotropy.; We utilize synchrotron radiation to study two mechanisms of OR: preferential c-axis distribution along the grooves and stress anisotropy in the Cr and Co films. Diffraction data shows that a preference for c-axis orientation exists and increases with increasing deposition bias. An analysis of the d-spacing vs. orientation angle for various Cr and Co peaks shows that both films are in compression when deposited over the temperature range 125–235°C and with bias ranging from 0–400V. The grooves cause a strain anisotropy in the Cr and Co films such that the parallel strain is more compressive than the perpendicular strain. A calculation of the Co-Cr misfit energy suggests that the Cr strain anisotropy breaks the bicrystal symmetry and favors the c-axis alignment along the grooves. The stress anisotropy in the Co layer is of the correct sign to favor OR > 1. A map of local magnetization changes during film reversal shows that disruption in the coupling due to texture lines causes a broader switching field distribution in the perpendicular direction.; The parameters relevant to c-axis orientation, stress anisotropy, and texture lines were used in a micromagnetic model to determine the OR due to each of these sources. The modeling showed that the experimentally observed c-axis alignment along the grooves produces the largest OR. The texture lines result in a lower OR but can account for the perpendicular hysteresis loop closing outside the parallel loop. The stress anisotropy increases the coercivity in both directions but contributes the smallest OR of the three sources. A combination of these anisotropy sources leads to hysteresis loop shapes and OR values similar to those observed experimentally.