B.R. Acharya

Advanced synthetic ferrimagnetic media (invited)

The exchange coupling field (Hex) in two-layer synthetic ferrimagnetic media (SFM) is enhanced to extend the areal density capability of earlier structures. The thermal stability of SFM is improved by employing high magnetic anisotropy stabilizing layers without significantly affecting the required write fields. However, this necessitates larger Hex values than were earlier realized, to preserve the antiparallel layer magnetic configuration at remanence. Hex is improved by inserting thin high Co content hcp layers, called “E-layers,” between the Ru layer and the magnetic layers. Large Hex values from 1 to 4 kOe are obtained depending on the E-layer composition and thickness. As the intergranular coupling is affected by the Co-rich E-layers, a method is provided that improves Hex to values >1 kOe without degrading read-write properties.

Study of the origin of orientation ratio in high-density longitudinal magnetic recording media

A study on the origin of orientation ratio in high-density recording media on mechanically textured substrates is reported. C-axis distribution of Co grains in textured case observed using high resolution TEM images shows its preferred orientation along the circumferential (along the groove) direction. The asymmetrical easy axis distribution is seen by maximum torque observed in different directions along the plane of the film. Diffraction patterns from several individual grains of the Cr underlayer are analyzed and indicated the preference of Cr along the circumferential direction. This could be the reason for C-axis of Co grains to show the preferred anisotropy along circumferential direction.

SNR improvements for advanced longitudinal recording media

Schemes for SNR enhancement for advanced longitudinal recording media are discussed. SNR improvement is obtained by utilizing a bi-magnetic layer media, where the initial magnetic layer has lower magnetization, coercivity, and magnetic anisotropy, in comparison to the top magnetic layer. Further improvements in SNR and thermal stability are achieved using synthetic ferrimagnetic media. The selection of proper thickness and composition of the initial magnetic layer is important for the high performance of the synthetic ferrimagnetic media.

Improved thermal stability of synthetic ferrimagnetic media with enhanced exchange coupling strength

The effect of the antiferromagnetic interlayer exchange coupling strength J between the initial or stabilization magnetic layer L1 and the top magnetic layer L2 on the thermal stability of synthetic ferrimagnetic media (SFM) is investigated. Enhanced J is achieved by the insertion of a thin Co-rich hexagonal close-packed layer between the Ru layer and L1, and such a structure did not change the read/write properties significantly. The contribution of the anisotropy energy of L1 to the thermal stability of SFM is improved by increasing J. However, a significant increase in the contribution of L1 to the thermal stability is achieved at relatively low J values (0.14 erg/cm2) which translate into only a 3–4% increase in the switching field H0.

Signal-to-noise ratio and thermal stability issues in extending synthetic ferrimagnetic media technology over 100 Gb/in/sup 2/

Signal-to-noise ratio (SNR) and thermal stability issues are addressed to evaluate synthetic ferrimagnetic media (SFM) for achieving areal densities >100 Gb/in/sup 2/. Thermally stable SFM is obtained at M/sub r//spl delta/ values as low as 0.15 memu/cm/sup 2/, utilizing a higher magnetic anisotropy for the stabilization magnetic layer. The SNR relations for SFM are decided by the effective M/sub r//spl delta/ and coercivity, similar to conventional media. The recording characteristics of a low M/sub r//spl delta/ medium was compared with a higher M/sub r//spl delta/ medium used for the 106-Gb/in/sup 2/ demonstration. Lower medium noise and higher signal resolution of the lower M/sub r//spl delta/ medium indicate an areal density extension to beyond /spl sim/150 Gb/in/sup 2/.

Thermal effects and in-plane magnetic anisotropy in thin-film recording media

The effect of thermal activation on the in-plane magnetic anisotropy [measured as orientation ratio (OR)] of granular longitudinal magnetic recording media is investigated. Temperature and time dependent studies were made on media with different magnetic layer thicknesses. We find that OR is independent of temperature for a stable medium but shows a large increase with temperature for thermally unstable media. At low temperatures and high field sweep rates, the OR values are found to be the same, independent of the magnetic layer thickness. The unique value when thermal activation is reduced is consistent with the high population of the cobalt c axes along the texturing direction as the origin of anisotropy.

Over 100 Gbits/in/sup 2/ longitudinal magnetic recording

Summary form only given. A recording density of 106 Gbits/in/sup 2/ has been achieved using a high-sensitivity spin-valve head and a thermally stable synthetic ferrimagnetic medium (SFM). The use of a highly stable medium allowed the demonstration to be made with a bit aspect ratio of 5.3 which is higher than the projected value. Some selected parameters are given for the demonstration.

Approaches to reduce temperature coefficient of coercivity of high-density recording media

The magnitude of temperature coefficient of coercivity (|dH/sub C//dT|) of high-density recording media increases with decreasing media thickness and dilution of the Co in the interior of the grains by Cr or other substitutions. A reduction in magnetic anisotropy with temperature increases |dH/sub C//dT| whereas a decrease in magnetization compensates for such change. Some approaches such as better Cr segregation, or utilizing a magnetic bilayer with the initial layer having a lower Curie temperature can be used to minimize |dH/sub C//dT|.

Extendibility of synthetic ferrimagnetic media for recording densities beyond 100 Gb/in/sup 2/

Summary form only given. In spite of projected limits for longitudinal recording, 106 Gb/in/sup 2/ was demonstrated using synthetic ferrimagnetic media (SFM) with extremely good thermal stability. In this paper, we project the areal density advantages of SFM from thermal stability, SNR, and materials perspective for densities above 100 Gb/in/sup 2/.