Microstructure and intergranular coupling in CoCrTa thin-film media fabricated using an ultraclean sputtering process

The microstructure and intergranular coupling in Co_85.5Cr_10.5Ta₄ and Co₇₈Cr₁₇Ta₅ media fabricated using an ultraclean (UC) process are discussed in relation to the thickness of the Cr underlayer. The purification of the deposition atmosphere by applying the UC process is found to be most effective for deriving high H_c in both media. In UC-Co₇₈Cr₁₇Ta₅, a high H_c of about 2.1 kOe remains even at a Cr thickness of 2.5 nm. With the UC process the Cr segregated grain boundary structure is enhanced even in media with thin Cr underlayers, which causes a remarkably low intergranular exchange coupling. The increase in the strength of intergranular magnetostatic coupling due to the grain size reduction strongly influences the reduction in H_c/H_k^grain with decreasing Cr thickness. In UC-Co₇₈Cr₁₇Ta₅ with extremely thin Cr underlayers, the sufficiently segregated grain boundary structure and the intrinsically low intergranular magnetostatic coupling are responsible for the realization of very high H_c/H_k^grain.