Ｃｏ（‐Ｂ）／Ｐｄ人工格子垂直磁気記録媒体の磁気異方性と磁化の熱擾乱

Abstract

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, δCo or δCoB. The perpendicular magnetic anisotropy Ku of these media shows maximum values of 5.7 x 106 erg/cm3 (Co/Pd) and 3.2 x 106 erg/cm3 (Co-B/Pd) at δCo or δCoB of around 0.2-0.3 nm. The KuV/kT (V; the activation volume, k; the Boltmann constant, T; the absolute temperature) of the Co/Pd medium has large values of more than 200 (δCo>0.3nm), while the KuV/kT in both media significantly decreases as the thickness decreases, which is not coincident with the thickness dependence of Ku. The value of Ku/2πMs2 (Ms; the saturation magnetization) in both media increase monotonically as the thickness decrease, and is ∼10 at δCo or δCoB of around 0.2-0.3 nm. The signal-to-medium-noise ratio SNmR of the Co-B/Pd media is higher than that of the Co/Pd media, and increase as δCoB decrease. TEM images and magnetic characterization revealed that these differences in SNmR are mainly due to the difference in the strength of intergranular exchange coupling.