The influences of Co-Cr-Pt-Ta sputtering-target microstructure on C/Co-Cr-Pt-Ta/Cr/glass films were investigated. The sputtering target consisted of a Co solid solution matrix and Ta- and Pt-rich precipitates. Annealing and rolling can increase the Pt and Ta content of the matrix. When the film is made by using an annealed and rolled target, its H_c and S* become large and the H_c distribution becomes small. These changes are related to the film composition. Simple calculations related to the ejection angular distribution of sputtered particles and yields suggest that about compositional changes in films are brought by the differences in the target microstructures.

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A new analytical formula for thermal fluctuation in magnetic recording media is presented. The thermal fluctuation of isolated particles in the presence of a small magnetic field is evaluated by introducing a simple and precise energy barrier formula. The thermal decay and the remanent coercivity of the recording medium, which has grain size distribution and inter-granular exchange interaction, are numerically computed. These results are approximated by an equation in terms of the thermal fluctuation in the magnetic recording media. This analytical formula shows good agreement with previous experimental results, which indicates an increase in the activation volume in the presence of a small magnetic field. Both the increase in the activation volume and a decrease in the magnetic viscosity coefficient in the presence of a small magnetic field can be explained by the mixture of thermally reversed and re-reversed particles. Reducing the demagnetization field for the recording media is most effective for decreasing the signal decay. From this point of view, an AFC medium, which can reduce the demagnetization field without decreasing the magnetic anisotropy energy of the particles, has a strong potential for realizing higher recording density.

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