ＣｏＰｔＣｒ−ＳｉＯ２／Ｒｕ垂直磁気記録媒体における磁気特性のＰｔ，Ｃｒ組成依存性

Abstract

The magnetic properties and media noise performance of {(Co100-XCrX)100-YPtY}89-{SiO2}11/Ru media were investigated as functions of the Pt and Cr contents. The magnetic anisotropy energy Ku shows a broad maximum at a Pt content around Y = 20 at%, almost irrespective of the Cr content. The anisotropy energy of the grains, Kug, calculated by taking account of the volume fraction, reaches nearly 8 x 106 erg/cm3 even with a Cr content of X = 10 at%. The ratio of the magnetic anisotropy energy to the thermal energy, KuVact/kT, at this composition maintains a value of more than 100, oven with 10 nm thickness and a grain size of 7.7 nm, indicating a high potential to resist thermal agitation. The high Ku causes a largo remanence coercivity Hr and a loop squareness of 1 in the Pt content region around Y = 20. The activation diameter Dact increases gradually as the Pt content increases, while an increase of the Cr content reduces the Dact. The signal-to-media-noise ratio SNmR improves as the Pt content decreases, which accords well with the reduction in Dact. It is likely that a Pt content of Y = 15 - 20 at% is an optimum composition to attain both low media noise and high thermal stability. There is a trade-off between low noise performance and thermal stability as a function of the Cr content.