Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D5: Pake Prize Symposium: Magnetic Storage and Applications |
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Sponsoring Units: FIAP Chair: Stefan Zollner, Freescale Semiconductor Room: Colorado Convention Center Korbel 1A-1B |
Monday, March 5, 2007 2:30PM - 3:06PM |
D5.00001: Seventy Years of Magnetic Disk Drive Technology. Invited Speaker: The first hard disk drive, the IBM RAMAC, was shipped in September 1956. It was the size of a couple of refrigerators, contained fifty 24-inch diameter disks and stored information at an areal density of 2000 bits per square inch. Although ten years ago, the industry was widely perceived as facing a fundamental limit at 36 Gbit per square inch (Gbpsi) in the form of superparamagnetism, current disk drives provide areal densities in excess of 130 Gbpsi and capacities of 750 Gbytes. Although the original projections of superparamagnetism were correct, by changing the way the devices were scaled and, ultimately by changing from longitudinal to perpendicular recording, it has been possible to circumvent superparamagnetic effects. Our current understanding indicates that it may be possible to extend the areal density by yet another factor of 400 from present densities, if advanced technologies such as heat assisted magnetic recording and bit patterned media are implemented. Assuming this proceeds at the recent rate of 40 percent increase in areal density per year, we would reach roughly 50 Terabit per square inch (Tbpsi) in about 2026, 70 years after the development of the first disk drive. To achieve this, however, the industry will need higher sensitivity giant magnetoresistive sensors, high efficiency near-field transducers powered with surface plasmons and self-assembled or nano-imprinted magnetic particle arrays for media. In this presentation, the author will briefly describe the history of recording on magnetic disk drives, then describe the potential for future growth and some of the physics and materials problems that need solution in order to realize this full potential. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:42PM |
D5.00002: New Developments in Perpendicular Magnetic Recording Media Invited Speaker: Recording areal density in current drives is approaching 200 Gb/in$^{2}$. While compositions of individual layers do generally vary, the structure of the PMR media in today's drives is remarkably similar with synthetic antiferromagnetically coupled soft underlayer (SAF SUL) structures, Ru based nucleation layers and oxide segregated recording (storage) layers [e.g., 1,2]. As areal density increases and track width is correspondingly decreased, a serious writability problem develops limiting the usable coercivity. This limitation, combined with the need to decrease grain size to improve signal-to-noise ratio (SNR), imposes serious constrains in the design of improved PMR media. New media structures using dynamic tilting switching mechanisms such as exchange coupled composite media (ECC) [3] and exchange spring media [4] have been proposed in order to overcome these obstacles. In this paper we will discuss the merits and limitations of current PMR media structures and propose possible improvement direction for media applicable for $>$ 200 Gb/in$^{2}$ recording including results from our latest attempts to reduce exchange spring media and related conceptual structures into practice. [1] G. Choe, A. Roy, Z. Yang, B.R. Acharya, and E.N. ABarra, \textit{IEEE Trans. Magn}., vol. 42, no. 10, pp. 2327-2329, Oct. 2006 [2] U. Kwon, H.S. Jung, M. Kuo, E.M.T. Velu, S.S. Malhotra, W. Jiang, G. Bertero, R. Sinclair , \textit{IEEE Trans. Magn}., vol. 42, no. 10, pp. 2330-2332, Oct. 2006 [3] R. Victora and X. Shen, \textit{IEEE Trans. Magn}., vol. 41, no. 2, pp. 537-542, Feb. 2005 [4] D. Suess, T. Schrefl, M. Kirschner, G. Hrkac, F. Dorfbauer, O. Ertl, J. Fidler, \textit{IEEE Trans. Magn}., vol 41, no.10, pp. 3166-3168, Oct. 2005. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 4:18PM |
D5.00003: New Developments in MRAM Invited Speaker: Bringing a new technology from Research and Development to first commercialization requires overcoming numerous technical challenges while maintaining continuous business commitment. Magnetoresistive Random Access Memory (MRAM) is a recent example of this process. MRAM combines magnetic devices with standard silicon to obtain the combined attributes of non-volatility, high-speed operation, and unlimited read/write endurance not found in any other existing memory technology. The first successful commercialization of MRAM was enabled by the convergence of several solutions to underlying challenges in the technology. One of the keys to manufacturability was the invention of the Toggle Write mode that provides robust magnetic switching margin. For high-speed read, a key solution was the ability to deposit and pattern high-quality, high-TMR magnetic tunnel junctions with narrow bit-to-bit resistance variation, low defect density and long-term reliability. In this talk, I will present details of each of the above technology elements, the performance and reliability of the 4Mb product, and the outlook for extending and scaling MRAM to other markets and nodes. [Preview Abstract] |
Monday, March 5, 2007 4:18PM - 4:54PM |
D5.00004: High Anisotropy Magnetic Recording Media Invited Speaker: Areal densities in magnetic recording have exhibited Moore's Law like increases in the last ten years. This is partially due to improvements in the media microstructure where reduced grain sizes, tighter grain size distribution, and chemical isolation between grains to break exchange provided increased signal-to-noise from decreased transition noise. With the recent shift from longitudinal to perpendicular recording, areal densities have again continued to increase with demonstrations of over 250 Gbits/in$^{2}$. However, areal density is limited by thermal stability considerations where the ratio of stored magnetic energy K$_{u}$V (anisotropy energy times the magnetic switching volume) to the thermal energy kT must be $\sim $ 50-70. The projected limit for traditional CoPtCr(X) granular media is on the order of 500 Gbits/in$^{2}$. Further increases in the areal density will require greater reduction in the grain size (switching volume), which necessitates finding media with higher anisotropy to maintain thermal stability. Possible candidate materials systems include FePt and SmCo$_{5}$, which have bulk K$_{u}$ values 50 to 100 times greater than CoPtCr(X) media materials. High K$_{u}$ allows for thermally stable grains sizes down to $\sim $ 2.5 nm, which would permit areal densities in the Tbit/in$^{2}$ regime. Accompanying this increase in K$_{u}$ is an increase in the media switching field (H$_{0})$, which is proportional to the ratio K$_{u}$/M$_{s}$ where M$_{s}$ is the saturation magnetization. Therefore, while providing thermal stability, these high K$_{u}$ materials would potentially require writing fields greater than 50 kOe which far exceed those of available recording head materials. One possible solution is heat-assisted magnetic recording (HAMR) where a laser locally heats the media in order to reduce the coercivity so that available head fields are sufficient. Numerous challenges exist for HAMR including high cooling rates so that the heating process does not render adjacent bits thermally unstable. This paper will review recent progress in this area and concentrate on the challenges for the production of high anisotropy media for Tbit/in$^{2}$ areal densities, such as maintaining grain sizes of 2 to 4 nm with the correct crystallographic texture and sufficient grain isolation to break exchange. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:30PM |
D5.00005: Automotive Applications of Physics and Materials Research: Permanent Magnets, Thermoelectrics, and Hydrogen Storage Invited Speaker: Advances in the research and development of new materials continue to have a major impact on the automotive industry and on many other technologies today. A physics background in materials provides a research scientist with many opportunities to pursue a very satisfying and successful career doing industrial and applied physics, ranging from discovering and characterizing new and technologically useful materials to always learning something new in science. For example, the use of permanent magnets in the auto industry was revolutionized by the discovery at General Motors Research and Development Center of a new iron based magnetic material Nd$_{2}$Fe$_{14}$B. Moreover, this material rapidly became the state-of-the-art permanent magnet in a wide range of applications across many technologies beyond automotive. More recently, with growing pressure to improve efficiencies of automobiles and other energy consumers, thermoelectrics are a very exciting class of energy conversion materials that have seen dramatic advances in performance. General Motors is at the leading edge of research and development on automotive waste heat recovery using thermoelectric materials. Today, the very promising fuel cell future of the auto industry relies, in part, on advances in on-board alternative fuel storage. New materials and schemes for hydrogen storage that will help bring automotive fuel cell technology to fruition is a rapidly advancing field of physics and materials research. In this presentation, I will discuss my work in these areas during my career at General Motors Research and Development Center. [Preview Abstract] |
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