Role of bottom layer of double recording layer structure for antiferromagnetically coupled longitudinal media

Double recording layers stacked on a Ru spacing layer are commonly used to obtain good recording properties for antiferromagnetically coupled (AFC) longitudinal media. In this paper, we report on a study that clarified the role of the bottom recording layer (BRL). We measured physical magnetic properties such as magnetic anisotropy field (H_k ), magnetocrystalline anisotropy energy (K_u), intergranular interaction, and thermal agitation of the AFC media, with and without BRL. Results showed that: 1) even a thin BRL (1 nm thick) significantly increases remanent coercivity H_cr; 2) this increase in H_cr is mainly caused by an increase in H_k due to elimination of the low K_u region at the bottom portion of the top recording layer; and 3) judging from magnetic cluster size, insertion of a BRL can reduce the intergranular exchange coupling at the initial growth region of the recording layer