Bruce Alvin Gurney

Bit-Patterned Magnetic Recording: Theory, Media Fabrication, and Recording Performance

Bit-patterned media (BPM) for magnetic recording provides a route to thermally stable data recording at >1 Tb/in2 and circumvents many of the challenges associated with extending conventional granular media technology. Instead of recording a bit on an ensemble of random grains, BPM comprises a well-ordered array of lithographically patterned isolated magnetic islands, each of which stores 1 bit. Fabrication of BPM is viewed as the greatest challenge for its commercialization. In this paper, we describe a BPM fabrication method that combines rotary-stage e-beam lithography, directed self-assembly of block copolymers, self-aligned double patterning, nanoimprint lithography, and ion milling to generate BPM based on CoCrPt alloy materials at densities up to 1.6 Td/in2. This combination of novel fabrication technologies achieves feature sizes of <;10 nm, which is significantly smaller than what conventional nanofabrication methods used in semiconductor manufacturing can achieve. In contrast to earlier work that used hexagonal arrays of round islands, our latest approach creates BPM with rectangular bit cells, which are advantageous for the integration of BPM with existing hard disk drive technology. The advantages of rectangular bits are analyzed from a theoretical and modeling point of view, and system integration requirements, such as provision of servo patterns, implementation of write synchronization, and providing for a stable head-disk interface, are addressed in the context of experimental results. Optimization of magnetic alloy materials for thermal stability, writeability, and tight switching field distribution is discussed, and a new method for growing BPM islands from a specially patterned underlayer-referred to as templated growth-is presented. New recording results at 1.6 Td/in2 (roughly equivalent to 1.3 Tb/in2) demonstrate a raw error rate <;10-2, which is consistent with the recording system requirements of modern hard drives. Extendibility of BPM to higher densities and its eventual combination with energy-assisted recording are explored.

Anomalous Enhancement of the Magnetic Anisotropy of CoCrPt Alloy Thin Film With Ultrathin Pt Interface

An anomalous enhancement of the coercive field (Hc) and of the perpendicular magnetic anisotropy (PMA) of CoCr10Pt10 (at.%) alloy thin films is observed when the magnetic layer is deposited on an ultrathin Pt interlayer (IL). The dc magnetic properties of Pt/CoCr10Pt10 are studied as a function of the magnetic alloy thickness (4-8 nm) and the Pt IL thickness (up to 3 nm). Both the coercive field and the interface anisotropy (Ks) exhibit a non-monotonic dependence on the Pt thickness, showing a characteristic peak value at an intermediate thickness, with a rise in the PMA up to 25%. Similar thickness dependence of Hc is observed when using Pd and Ir ILs, but with a more moderate enhancement. This approach provides a means to control and engineer the PMA of CoCrPt alloys, and may find an application in data storage and low-power spinelectronics.