| This investigation is a basic study of the influence of alloy composition (Ta and Pt) and processing parameters on the microstructure and resulting magnetic properties of CoCr sputtered longitudinal recording media. Magnetic thin films, 25 nm thick, of Co84Cr16, Co80Cr 16Ta4, Co80Cr16Pt4, and Co76Cr16Pt4Ta4 were D.C magnetron sputtered onto identical substrates with a CrMo seed-layer. Disks were sputtered at 9 different substrate conditions for each alloy by varying the substrate temperature (150°C, 200°C, and 250°C) and sputter bias (no bias, −200 V, and −300 V). The magnetic properties were measured using Vibrating Sample Magnetometry (VSM). Quantitative elemental maps of Cr composition from these samples were produced by using energy-filtered transmission electron microscopy (EFTEM) with spatial resolution of ∼1nm to analyze the grain boundary Cr enrichment and grain interior depletion. Quantitative EFTEM Cr data from the grain interiors determine the local magnetocrystalline anisotropy (Ku) and allow calculation of the product of Ku and the grain volume (KuV).; The results of this research show that alloys with Pt and Ta have different effect on the interfacial energy and misfit of the sputtered layers, which subsequently affects the growth modes, Cr segregation profiles, density of special grain boundaries (such as 90° boundaries) and the magnetic properties. Alloying CoCr with Ta reduces the misfit and interfacial energy and promotes layer-by-layer growth mode. This growth mode is responsible for the low density of special grain boundaries, enhances the Cr segregation to the grain boundaries and increases the Ku due to grain interior depletion of Cr, which strongly decouples the grains and increases the coercivity. However, the CoCr and CoCrPt have shown reduced coercivity and greater intragranular segregation compared to the CoCrTa and CoCrTaPt samples. Mismatch between the CoCrPt magnetic layer and the CrMo underlayer results in an island growth mode with a high density of 90° grain boundaries, high density of intragranular density and more complicated Cr segregation pattern. Comparing identical areas analyzed with both high-resolution TEM images and EFTEM maps revealed that the origin of the intragranular segregation can be related to the island growth mode exhibited by the CoCr and CoCrPt. Increased substrate temperature result in increased coercivity only if the amount of Cr at the grain boundaries allows magnetic decoupling between the grains such as in the case of Ta containing materials. Substrate bias has only a slight effect on the Cr segregation of the sputtered alloys. |
