Effect of magnetic softness in a soft layer on media properties of hard/soft stacked composite perpendicular media

Abstract

Adding Pt into CoCr-oxide alloy for controlling magnetic softness in a soft layer on hard/soft ͑H/S͒ stacked composite media significantly affects magnetic properties and microstructure. H c values for capping layer ͑CL͒ media with a relatively high-H k soft layer initially increase with increasing t cap . However, H c values are relatively constant for H/S media with Pt 3% and 10% soft layers and reduced for the media with a CoTaZr-SiO 2 soft layer having in-plane H k . The simulation results explain these experimental H c trends by the compensation effect between the decrease in average K u due to the use of less-K u soft layer and the increases in volume with increasing t soft . Reduction in H c with increasing t soft is anticipated when K u in a soft layer reduces by Ͼ27%. As the Pt content in a soft layer increases from 3% to 18%, higher H c and H n but lower H s are observed. Plan-view transmission electron microscopy images for the medium with Pt 18% soft layer show no subgrains and thinner grain boundary width and explain the significant increase in lateral A ex . Thus, the Pt content in a soft layer needs to be optimized. Compared to CL media, H/S composite media with the Pt 5% and 8% soft layers improve both SNR me and media writability.Advanced hard/soft ͑H/S͒ composite media structures with a concept of dynamic magnetic switching are currently in development for further improvement of areal density. A soft layer exchange coupled with the hard layer provides shallow angular dependence of remanent coercivity ͑H cr ͒, providing the improvement of media writability and signalto-noise ratio ͑SNR͒. Incoherent switching behavior via a soft layer occurs in exchange-coupled composite ͑ECC͒, 1 exchange spring, 2 and anisotropy graded 3 media while coherent switching behavior is anticipated in H/S media with a thin soft layer. 4 Compared to conventional capping layer ͑CL͒ media with a high magnetic anisotropy field ͑H k ͒-soft layer, ECC media can improve media writability, SNR, and biterror-rate but head dependence effect needs to be considered. The simulation results 5 showed the best performance in ECC media with the parameters of H k = 6 kOe, intergranular exchange coupling constant ͑A ex ͒ =1ϫ 10 −7 erg/ cm in a soft layer, and interlayer exchange coupling strength ͑J in ͒ between soft and hard layers= 2 ergs/ cm 2 . Tanahashi et al. 6 recently demonstrated that even H/S dual media with graded properties achieve high areal density of 612 Gbytes/ in. 2 .Head field gradient and field strength typically trade off in trailing shielded-pole ͑TS͒ write heads. 7 Head-media optimization is critical when media are not matched to head writability. More media dependence was observed in TS heads with a single coil with less field strength but higher field gradient compared to TS heads with double coils. 8 Writability enhancement in the recording layer can further improve SNR but this enhancement needs to be optimized by thermal stability factor ͑K u V / kT͒, adjacent track erasure ͑ATE͒, and return field-induced partia...