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 Co_85.5Cr_10.5Ta₄ and Co_62.5Ni₃₀Cr_7.5 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.