Thermal agitation of magnetization and recording performance of Co(B)-Pd superlattice perpendicular recording media

Magnetic properties and recording performance are discussed for Co-Pd(1 nm)]₉ and [(Co-27 at% B)/Pd(1 nm)]₉ superlattice perpendicular recording media as a function of the Co or Co-B layer thickness δ_Co or δ_CoB. The Co-Pd media shows large values of perpendicular anisotropy K_u of 5.7 × 10⁶ erg/cm³ (δ_Co ≅ 0.25 nm) and K_uV_act/kT of more than 200 (δ_Co > 0.3 nm), indicating a high potential to resist thermal instability (V_act activation volume, k Boltzmann constant, T absolute temperature). However, the thickness dependence of K_uV_act/kT was not simply coincident with that of K_u. Magnetic characterization reveals that intergranular exchange coupling decreases as the δ_Co or δ_CoB decreases, leading to a higher signal-to-medium-noise ratio SN_mR. The addition of B to the Co layer reduces the values of K_u and K_uV_act/kT significantly, however, and is effective to reduce intergranular exchange coupling and activation volume, resulting in higher SN_mR.