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Control of Exchange Coupling Between Granular Oxide and Highly Exchange Coupled Cap Layers and the Effect on Perpendicular Magnetic Switching and Recording Characteristics | IEEE Journals & Magazine | IEEE Xplore

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


Abstract:

We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxid...Show More

Abstract:

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.
Published in: IEEE Transactions on Magnetics ( Volume: 45, Issue: 6, June 2009)
Page(s): 2694 - 2700
Date of Publication: 19 May 2009

ISSN Information:


I. Introduction

Perpendicular recording technology has advanced significantly with areal density approaching 300 Gb/in2 in commercially available products today. In order to sustain high areal density with adequate thermal stability, advanced media structures such as exchange spring (ES) or exchange coupled composite (ECC) media comprising hard and soft layers in the grain [1], [2] or coupled granular/continuous (CGC) media [3] have been proposed to improve writeability of high anisotropy grains. These approaches are designed to reduce the switching field of the high grains that are exchange-coupled to the soft layer which starts switching at a lower applied field than that of the hard layer while adequate thermal stability is maintained. Several research groups attempted to fabricate the media structure to explore the proposed advantages of ECC media as well as CGC media [4], [5]. Although the enhanced media writeability was successfully demonstrated, the predicted noise reduction necessary for high density recording was insignificant. The key challenge to enhance the media signal-to-noise ratio (SNR) in the composite media is to fabricate the reduced grain in the hard layer with higher , prior to stacking the soft layer onto the hard layer.

References

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