Intergranular coupling and recording properties of CoCrTa and CoNiCr thin-film media fabricated using an ultraclean sputtering process

Magnetic properties, microstructure and their effect on media noise in Co85.5Cr10.5Ta4 and Co62.5Ni30Cr7.5 thin-film media fabricated using an ultraclean (UC) sputtering process are discussed as a function of the thickness of the Cr underlayer. By applying the UC process, high H-c values are realized even in these media with extremely thin Cr underlayers. In UC-CoCrTa, a high H-c of about 1.5 kOe remains even at a Cr thickness of 2.5 nm. The formation of a Cr segregated grain boundary structure is strongly enhanced by applying the UC process, which reduces the intergranular exchange coupling in these media. High S/N-m ratios are obtained even in CoNiCr media due to the remarkable decrease in intergranular exchange coupling. In the media with grains sufficiently separated by the segregated grain boundary, the reduction of the grain size with decreasing Cr thickness is found to be most effective for the improvement of S/N-m.