Thermal Stability and Recording Performance in Co-PrTb/Co-Cr-Ta Composite Perpendicular Magnetic Recording Media

摘要

The thermal stability and medium noise performance of Co_(100-x)(PrTb)_x/Co-Cr-Ta (X=21-31.7 at percent) composite perpendicular media are discussed. The perpendicular magnetic anisotropy K_u shows a maximum at X=approx 25, although the saturation magnetization decreases gradually as X increases. The ratio of "intrinsic" remanence coercivity obtained by subtracting the thermal agitation to the anisotropy field, H_0/H_k, increases as X increases, indicating a reduction of the exchange coupling of magnetization. The medium noise of the composite media, which have CoZrNb soft back-layers, decreases gradually as X increases and as the Co-PrTb thickness decreases, resulting in a higher signal-to-medium-noise ratio SN_mR. The SN_mR of a Co_(76.5)(PrTb)_(23.5) (5nm)/Co_(77)Cr_(19)Ta_4 (25nm) composite medium is about 8 dB higher than that of a Co_(77)Cr_(19)Ta_4 (30 nm) medium at 300 kFRPI. The composite media show high thermal stability of read-back signals even at low recording density. However, the thermal signal-decay increases gradually as the Co-PrTb thickness decreases, and also as X increases, indicating that the thermal stability has a trade-off relation with the medium noise performance.