HIGH COERCIVE FORCE AND LOW INTERGRANULAR COUPLING IN THIN-FILM MEDIA FABRICATED UNDER THE ULTRA CLEAN SPUTTERING PROCESS

The ultra clean sputtering process (UC process) was newly introduced in the fabrication of Co62.5Ni30Cr7.5 and Co85.5Cr10.5Ta4 thin film media to establish the new concept of controlling the microstructure. By applying the UC process, extremely high H-c values of up to 3 kOe were realized without decreasing the saturation magnetization in both kinds of media. A high H-c value was derived even in the media with very thin Cr underlayers. Magnetic torque analysis has revealed that the magnetocrystalline anisotropy field of grains, H-k(grain), is about 20-50% larger than that in the normally processed media, which is one of the dominant factors in realizing high H-c values. The realization of large H-k(grain) values was found to be mainly caused by the decrease in the Cr content of the grains. The enhancement of the homogeneously segregated grain boundary structure, which corresponds to a decrease in the intergranular exchange coupling, was also found to induce high H-c values in these media. This desired segregated structure was observed even in the media with an extremely thin Cr underlayer of 2.5 nm. The low intergranular coupling realized induced very low media noise even in the CoNiCr media. The UC process is concluded to be an essential technology for fabrication of high density thin film recording media.