High coercive force and low intergranular coupling in CoCrTa thin-film recording media fabricated under ultra clean sputtering process

Ultra clean sputtering process (UC-process) was newly introduced in the fabrication of Co_85.5Cr_10.5Ta₄ thin-film media to establish the control of microstructure of films. By applying the UC-process, the remarkable high-H_c value of about 2.8 kOe (15 nm/50 nm in CoCrTa/Cr thicknesses) was realized with no decrement in saturation magnetization. High-H_c of about 2 kOc (40 nm in magnetic layer thickness) remains even for extremely thin Cr thickness of about 5 nm. Magnetic torque analysis has revealed that magnetic anisotropy field of grains H^grain_k in the UC-processed media shows large values of about 6-7.5 kOc, which are about 20-50% larger than those of media fabricated under the normal sputtering process commonly used. The result of temperature dependence of saturation magnetization suggests that the appearance of large H^grain_k is mainly attributable to the decrease in Cr content in grains. On the other hand, the enhancement of the formation of homogeneously segregated grain boundary structure, which corresponds to the decrease of intergranular exchange coupling, was also found. The ultra clean sputtering process enables the control of the fine structure and induces the excellent features for magnetic properties even in commonly used CoCrTa material.