Mohammad Taghi Mirzamaani

Demonstration of 35 Gbits/in/sup 2/ in media on glass substrates

A recording density of 35 Gbits/in/sup 2/ was achieved in longitudinal recording media with high-sensitivity GMR heads. The media displayed excellent thermal stability as a result of a CoPtCrB alloy with high magnetocrystalline anisotropy and relatively narrow grain size distribution. The degree of Co easy-axis orientation in the plane of the /spl mu/m was greatly improved and the grain size was reduced in the media on glass substrates. Estimates of the switching volume from dynamic coercivity and signal-to-noise measurements are larger than the physical grain size, suggesting that intergranular interactions improve stability. A potential path to further increases in recording density above 35 Gbits/in/sup 2/ is to use antiferromagnetically coupled magnetic layers in the media.

Control of Exchange Coupling Between Granular Oxide and Highly Exchange Coupled Cap Layers and the Effect on Perpendicular Magnetic Switching and Recording Characteristics

We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxide and continuous cap layers was varied. The interfacial exchange coupling strength was controlled by adjusting the magnetization (Ms) and the thickness (t) of the exchange control layer (ECL) between granular oxide and cap layers. The media switching mechanism highly depends on the oxide-to-cap exchange coupling strength as well as the relative moment ratio of cap and oxide layers. Reversal process is coherent for medium with only granular oxide layer and becomes incoherent with incorporation of ECL and continuous cap layers. Optimizing granular oxide-to-cap exchange coupling improves the media writeability as well as the media signal-to-noise ratio (SNRm). At optimum exchange coupling condition, the switching field is significantly reduced even with higher thermal stability factor (Ku V/kB T). However, when the interlayer coupling strength is too weak, independent switching of oxide and cap layers occurs, resulting in poor writeability and high media noise. An optimum design of oxide-to-cap exchange coupling is critical in attaining recording properties for high density recording through selection of appropriate ECL and cap materials.

A Study of Perpendicular Magnetic Recording Media With an Exchange Control Layer

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 (KuV/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.

Design Consideration and Practical Solution of High-Performance Perpendicular Magnetic Recording Media

The core of the current granular perpendicular magnetic recording (PMR) media is the granular oxide magnetic layer (GOML). We observe that a fcc NiW seed layer, followed by a hcp Ru layer sputtered under low pressure (LP-Ru) and then by a hcp Ru layer sputtered under high pressure (HP-Ru) provides an excellent structural template for the granular oxide magnetic layer (GOML). Microstructure and magnetic properties of the GOML can be tailored through process conditions and alloy compositions to maximize the recording performance of the perpendicular magnetic recording media. Exchange coupled composite (ECC) media design provides significant improvement in overwrite (OW) and signal-to-noise ratio (S0 NR) for perpendicular magnetic recording media. Recording performance of the ECC media needs to be optimized with consideration of the magnetic properties and thicknesses of both the exchange control layer (ECL) and the cap magnetic layer (CML). At their respective optimum, the recording performance of the ECC media is mostly dependent upon the properties of the GOML and CML. This study indicates that a dual magnetic cap layer structure consisting of low-Ms and high-Ms sublayers can combine the benefits provided by the two types of cap magnetic materials.

Head-to-SUL Spacing Reduction With a Magnetic Seed Layer and the Effect on Perpendicular Recording Characteristics

A new underlayer structure consisting of a magnetic seed was used to reduce the recording layer-to-soft magnetic underlayer (RTS) spacing and its effect on perpendicular recording characteristics was investigated. The RTS spacing is reduced by partially replacing the non-magnetic FCC NiW alloy layer with a magnetic CoNiFe layer that acts as a part of the underlying SUL through magnetic exchange coupling. Magnetic CoNiFe layer promotes predominant FCC (111) planes of NiW layer that enhances epitaxial growth of the subsequent Cr BCC (110), Ru and Co HCP (0002) layers. As a result of improved crystallography with magnetic seed, the Co (0002) c axis dispersion is reduced at lower RTS spacing. The head write-ability becomes stronger at lower RTS spacing and the influence of side fringing fields on the nearest adjacent track erasure is highly dependent on the write head type at different RTS spacing. In addition, the change in RTS spacing also affects the read-back response. The signal-to-media noise (SNRm) is improved at low linear densities regardless of RTS spacing but degrades at higher linear densities when RTS spacing becomes too low. It is important to optimize the RTS spacing and the head-to-media integration to improve overall system performance.

Oriented longitudinal media on glass substrates

This paper reports on the recent breakthrough of achieving high orientation ratio (OR) on directly textured glass substrates. We present a unique medium design combining seedlayer, underlayer, and an antiferromagnetically coupled (AFC) magnetic layer structure. Such a structure gives rise to a high OR and leads to significant improvement of recording performance. This technology has enabled the extension of glass disk media to ultra-high density longitudinal recording.

Film optimization of laminated antiferromagnetically coupled media

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.

Laminated antiferromagnetically coupled media - optimization and extendibility

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.