Exchange coupled composite (ECC) media have been proposed as a way to facilitate writing of perpendicular media to allow use of magnetic materials with higher magnetic anisotropy ( Ku ) to increase media thermal stability. This paper is an experimental study of ECC media. Our results show that overwrite (OW) of perpendicular media can be improved significantly by the addition of an exchange control layer (ECL), consistent with the original ECC media design proposal. However, such OW improvement can also be achieved with non-ECC media (without ECL) by thickening of the cap magnetic layer. We observe that at similar OW, the non-ECC media can have similar magnetic core width (MCW) to ECC media with even higher thermal decay energy barrier ( Ku V/kT). The advantage of the ECC media is, instead, media signal-to-noise ratio increase over the non-ECC media. It is also observed that magnetic property and recording performance of the ECC media strongly depend on the magnetic properties and thicknesses of both ECL and cap magnetic layer.

In this study, a new underlayer structure consisting of FCC NiW, BCC Cr and HCP Ru layers is investigated as a promising underlayer that offers good perpendicular magnetic and recording properties. The FCC (111) planes of NiW layer enhances hetero-epitaxial growth of the subsequent BCC Cr (110), HCP Ru and Co (0002) layers in the direction perpendicular to the film plane. After the NiW-Cr-Ru layer structure is optimized, the Co (0002) c axis dispersion is greatly reduced and ~ 3 degree of XRD rocking width is achieved. As a result, excellent magnetic properties such as high coercivity, high nucleation field and narrow switching field distribution (SFD) are obtained. In addition, low media jitter and high signal-to-media noise (SNR m) can be achieved. The SNR m is also highly dependent on head-to-SUL spacing which is altered by varying NiW or Cr layer thickness without affecting crystallography. Optimized head-to-SUL spacing is needed to gain head writeability as well as resolution.

Lamination of multiple isolated magnetic layers has been shown to be an effective method to significantly increase signal-to-noise ratio in longitudinal media. These laminated media, however, are accompanied by low overwrite and wide magnetic pulse width, mainly as a result of poor writing of the bit transitions in the magnetic layer further away from the head and an offset in the transition position in the multiple magnetic layers resulting from head field spacing loss. We have demonstrated that the transition writing and transition alignment in the multiple magnetic layers of the laminated antiferromagnetically coupled (AFC) media can be optimized by adjusting the magnetic anisotropy of the relevant magnetic layers to compensate for the reduction of the head field magnitude with spacing. Such optimization results in significant improvements in media recording performance, leading to successful application of this medium technology. In this paper, we will highlight some of these improvements and discuss our approaches to further improve the recording performance by reducing the thicknesses of the magnetic layers and the lamination spacer layer in the laminated AFC film stack and by introducing additional elements in the magnetic layer.

Longitudinal media with multiple isolated magnetic layers (laminated media) have been shown to have a significant signal-to-noise ratio (SNR) advantage over conventional media. However, the application of laminated media has been hindered by reduced overwrite and wider magnetic pulsewidth compared to conventional media. Some of the major causes for such degradation in recording properties are poor writing of transition in the magnetic layer farther from the head and an offset in the transition position in the multiple magnetic layers resulting from the decrease in head field magnitude with spacing. We find that the transition writing and transition alignment in the multiple magnetic layers of the laminated antiferromagnetically coupled (AFC) media can be optimized by adjusting the magnetic anisotropy of the relevant magnetic layers to compensate for the reduction of the head field magnitude with spacing. This optimization leads to significant improvements in media recording performance, such as an increase of overwrite, reduction of magnetic pulsewidth, and further increase of SNR. Such adjustment should also be applicable to laminated conventional (nonAFC) media.