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)]/sub 9/ and [(Co-27 at% B)/Pd(1 nm)]/sub 9/ superlattice perpendicular recording media as a function of the Co or Co-B layer thickness /spl delta//sub Co/ or /spl delta//sub CoB/. The Co-Pd media shows large values of perpendicular anisotropy K/sub u/ of 5.7 /spl times/ 10/sup 6/ erg/cm/sup 3/ (/spl delta//sub Co/ /spl cong/ 0.25 nm) and K/sub u/V/sub act//kT of more than 200 (/spl delta//sub Co/ > 0.3 nm), indicating a high potential to resist thermal instability (V/sub act/ activation volume, k Boltzmann constant, T absolute temperature). However, the thickness dependence of K/sub u/V/sub act//kT was not simply coincident with that of K/sub u/. Magnetic characterization reveals that intergranular exchange coupling decreases as the /spl delta//sub Co/ or /spl delta//sub CoB/ decreases, leading to a higher signal-to-medium-noise ratio SN/sub m/R. The addition of B to the Co layer reduces the values of K/sub u/ and K/sub u/V/sub act//kT significantly, however, and is effective to reduce intergranular exchange coupling and activation volume, resulting in higher SN/sub m/R.