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Magnetics, IEEE Transactions on

Issue 4 • Date July 2003

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  • History of magnetic disk storage based on perpendicular magnetic recording

    Page(s): 1871 - 1875
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    This paper reviews a major disk-drive product development effort in IBM during the 1950s, one that was originally based on perpendicular recording. The goal of the project, identified as the Advanced Disk File (ADF), was to develop the successor to the first disk drive, the Random Access Method of Accounting and Control (RAMAC) 350. The ADF eventually became the IBM 1301, the first disk drive to use a flying head per surface. Whereas the RAMAC used longitudinal recording, the ADF project chose perpendicular recording as the mainstream recording technology for magnetic disk data storage and continued on this path for a period of five years. A crisis arose in the later stages of prototype testing due to unacceptable failure rates; one decision made was to change the recording method from perpendicular back to longitudinal. The reasons for the original selection of perpendicular and the subsequent return to longitudinal recording are described and address technology, product, and business issues. General observations on factors influencing the choices made and the final outcome are offered as well as the long-term impact of these events on the disk-drive industry. View full abstract»

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  • Issues in heat-assisted perpendicular recording

    Page(s): 1972 - 1979
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1639 KB) |  | HTML iconHTML  

    Heat- or thermally assisted magnetic recording employing perpendicular media is considered. The technological and physical principles treated are also applicable to longitudinal recording. Three issues are treated: Optical heating of a small volume of the medium on the length scale of a recorded bit at areal densities beyond 1 Tb/in2, dissipation of waste heat generated on an integrated flying slider, and optimization of the recording process. View full abstract»

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  • Parametric optimization for terabit perpendicular recording

    Page(s): 1876 - 1890
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    The design of media for ultrahigh-density perpendicular recording is discussed in depth. Analytical and semianalytical models are developed to determine the constraints upon the media to fulfill requirements of writability and thermal stability, and the effect of intergranular exchange coupling is examined. The role of vector fields during the write process is examined, and it is shown that one-dimensional models of perpendicular recording have significant deficiencies. A micromagnetic model is described and the results of simulations of recording undertaken with the model are presented. The paper demonstrates that there is no physical reason why perpendicular recording should not be possible at or above 1 Tb/in2. View full abstract»

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  • High-frequency inductance measurements and performance projections made for cusp-field single-pole heads

    Page(s): 1949 - 1954
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    High-frequency measurements of the inductance of cusp-field single-pole heads for perpendicular recording are made out to 13.5 GHz to determine their performance. The inductance of the pole heads examined are typically 1.2-1.9 nH with a self resonance at about 7-10 GHz. Inductance versus current measurements allow construction of a nonlinear eddy-current damped, thin-film head model. Comparison is made to a longitudinal recording head of similar size and turns. The effect of the medium underlayer as part of the head return path is shown to have minimal effect on the head inductance. Contact Tri-Pad heads are used to demonstrate the changes produced by the underlayer and to demonstrate apex and yoke saturation. The contact behavior is similar to that for a longitudinal thin-film head. The frequency dependence of the pole material permeability is discussed. The conclusions provide a practical bit rate limit for the cusp-field head based on head and write channel modeling, experimental high-frequency inductance data, and spin reversal considerations. View full abstract»

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  • SNR improvement of granular perpendicular recording media

    Page(s): 1919 - 1924
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1462 KB) |  | HTML iconHTML  

    In this paper, we address important issues on the performance improvement of perpendicular magnetic recording (PMR) media, such as noise reduction by adjusting the soft magnetic underlayer (SUL) properties and recording layer and intermediate layer modifications for optimum signal-to-noise (SNR) performance. The permeability of the SUL plays a significant role in writability and SNR. Proper pinning of the SUL should be considered for reducing spike noise. A systematic comparison of alloy and oxide granular media shows that optimized oxide media can provide both better SNR and good thermal stability and is promising for high-density recording. View full abstract»

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  • The role of SUL in readback and effect on linear density performance for perpendicular recording

    Page(s): 1961 - 1966
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (470 KB) |  | HTML iconHTML  

    We present a micromagnetic modeling on the readback process of perpendicular recording with soft underlayer (SUL). The effect of the SUL on readback has been investigated. The SUL imaging effect enhances the readback signal amplitude differently for high density and low density, making the rolloff of the readback signal faster with the linear density and, thus, deteriorating the readback performance by lowering the maximum achievable linear density. Most approaches for increasing the density limit via making the SUL imaging less effective are accompanied by the tradeoff of the write field loss. Reducing the head-medium spacing and the reader gap with an optimized spin valve reader stripe height are essential for maximizing the linear density limits imposed by the rolloff of the readback. View full abstract»

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  • Spinel ferrite Co-γFe2O3 perpendicular media on exchange-coupled underlayers

    Page(s): 1936 - 1941
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    Spinel ferrite Co-γFe2O3 films have the advantages of high coercivity, high stability without a protective layer, and low noise performance for magnetic recording layers. Also, exchange-coupled Co-Zr-Nb/Co-Sm underlayers show superior characteristics. The Co-Sm hard magnetic layer pins the domains of the Co-Zr-Nb soft magnetic layer effectively and decreases the noise coming from the latter. By combining the Co-γFe2O3 recording layer and exchange-coupled Co-Zr-Nb/Co-Sm underlayers, the triple-layered perpendicular media show promise for ultrahigh-density perpendicular recording. View full abstract»

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  • Perpendicular recording heads for extremely high-density recording

    Page(s): 1942 - 1948
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    The basic design and recording performance of advanced probe heads with trapezoidal pole tips are described. Eighty advanced probe heads were chosen to study the effects of different media designs on parametrics and signal-to-noise ratio (SNR) performances. Excellent writability of the advanced probe heads is demonstrated by a series of overwriting (OW) and nonlinear transition shift (NLTS) saturation measurements. Write currents as low as 5 mAo-p are required for recording. Excellent OW can be obtained with both high and low OW ratios. Better than -14 dB of NLTS was measured at linear densities as high as 950 KFCI. While OW was observed to be insensitive to media designs under study, NLTS and media SNR were observed to be strongly dependent on the details of media designs. Adjacent track erasure margins of the advanced probe heads were observed to be excellent on both media under study. Minimal side-writing has been observed using the advanced probe heads with trapezoidal pole shape. The advanced probe heads have also been successfully integrated into 80 GB/P perpendicular magnetic recording drives. Finally, linear densities as high as 830 KBPI and track densities as high as 188.7 KTPI were achieved on optimal head/media combinations. Perpendicular magnetic recording at areal densities as high as 145.7 Gb/in2 have thus been demonstrated. View full abstract»

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  • CoPtCr-SiO2 granular media for high-density perpendicular recording

    Page(s): 1914 - 1918
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    SiO2 added CoPtCr magnetic layers are employed for perpendicular recording media. The microstructure, magnetic properties, and recording performance of these media are discussed. Very fine grains with size of less than 7 nm, surrounded by grain boundaries mainly consisting of silicon oxide, are realized. The addition of SiO2 to CoPtCr is very effective in enhancing the well-isolated fine grain structure without disturbing the epitaxial growth of the CoPtCr grains on the Ru underlayer. The media show a large perpendicular anisotropy Ku of ∼4 × 106 erg/cm3 and a KuV/kT value of more than 80, even at a CoPtCr-SiO2 thickness of 12 nm, resulting in a high coercivity Hc (∼4 kOe) and high squareness Mr/Ms of ∼0.96. The CoPtCr-SiO2 medium shows excellent signal-to-medium-noise ratio performance together with high thermal stability at very thin thickness, indicating great potential for high-density perpendicular recording media. View full abstract»

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  • Development of Co-alloys for perpendicular magnetic recording media

    Page(s): 1908 - 1913
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    Exploring new Co-alloy compositions to achieve both chemical segregation and suitable magnetic properties is a priority task for the development of future perpendicular magnetic recording media. With proper interlayer (IL) design, columnar Co-alloy grains with narrow orientation distribution (Δθ50< 6°) have been obtained on thin ILs (4 nm thick). We demonstrate CoCrPtB-alloys with full remanence squareness and large negative reverse field (Hr<-1.5 kOe) at low IL and magnetic layer thickness of 4 and 11 nm, respectively. It is also shown that carbon overcoat thickness reduction results in a signal-to-noise ratio gain of about 0.5 dB/nm. View full abstract»

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  • Monolayer of physically separated FePt islands with a tetragonal L10 structure produced by thermally created mass transport

    Page(s): 1925 - 1929
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    A monolayer of physically separated FePt islands has been produced by thermally created mass transport of ultrathin FePt film, whereby formation of a magnetic layer composed of a two-dimensional arrangement of physically separated magnetic grains for decrease of magnetic coupling between the grains can be realized. The monolayer with [001] orientation was produced on [100] oriented MgO film. The produced monolayer had a small and uniform grain size and tetragonal L10 structure. Formation of granular film composed of a three-dimensional arrangement of L10-FePt ordered grains with [001] orientation in MgO film has been achieved by stacking the monolayer of FePt islands with MgO separation layers for high-density perpendicular media. View full abstract»

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  • Adjacent-track interference in dual-layer perpendicular recording

    Page(s): 1891 - 1896
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    Adjacent-track interference (ATI) in a dual-layer perpendicular recording system arises during both writing and reading. During writing, the stray fields from the write head can cause side writing and side erasure. A dc-erase method using media with a low nucleation field is used to identify the extent and polarity of these fields. In media with a strong anisotropy in the soft underlayer (SUL), experimental results reveal that the fields causing ATI have a strong cross-track asymmetry due to interactions between the writing flux and the magnetization of the SUL. On readback, cross-track amplitude profiles taken at long wavelengths show a distinctive "side bump" predominantly on just one side of the track profile. This asymmetry is again found to be associated with the magnetization in the SUL. A theoretical study yields expressions for the lateral extent of the side reading and a critical bit length at which side reading becomes significant. Both of these are consistent with experimental observations. The onset of side erasure during writing is further equated with the time-dependent nucleation field of the medium. Theoretical arguments on thermal decay in the presence of external and demagnetizing field indicate that the threshold for ATI-associated side erasure is expected to follow a time dependence similar to Sharrock's formula for dynamic coercivity. View full abstract»

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  • Feasibility of discrete track perpendicular media for high track density recording

    Page(s): 1967 - 1971
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    The feasibility of discrete track media with perpendicular anisotropy for high track density is studied. The discrete tracks are separated physically and magnetically by the grooves. The actual media was fabricated to evaluate the basic write/read properties. The measurements have been done with a spin stand. As a result, discrete track media showed a better write efficiency and recorded signal separation between the adjacent tracks compared to the conventional continuous recording layer media. It indicates the potential of this media for high track density recording. View full abstract»

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  • Micromagnetic simulation of magnetic cluster, thermal activation volume, and medium noise in perpendicular recording media

    Page(s): 1897 - 1901
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    The process of formation of magnetic clusters in perpendicular recording media was investigated through micromagnetic simulation and compared with data for longitudinal recording media. The size of magnetic clusters, which is obtained from the autocorrelation length of the demagnetized state by a dc reverse field, was almost the same as that for written states. It increased with increasing intergrain exchange coupling and was independent of the process of cluster formation. Also, the thermal switching unit size (activation volume) was found to be smaller than the magnetic cluster size. It remained almost the same as the grain size until the exchange coupling reached a critical value, and then increased further. The transition noise, the main part of the medium noise, increased with increasing magnetic cluster size. View full abstract»

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  • Recording field analysis of narrow-track SPT head with side shields, tapered main pole, and tapered return path for 1 Tb/in2

    Page(s): 1955 - 1960
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    Results are presented for a three-dimensional finite-element method simulation of a head/medium model for 1 Tb/in2 (540 ktpi with 38-nm track width and 47-nm track pitch, 1.8 Mbpi with minimum bit length of 11 nm). We have simultaneously introduced three new structures, side shields, tapered main pole, and tapered return path for the head in order to satisfy the requirement for a large recording field, small stray field to the adjacent tracks, and a field distribution that is robust for skew problems, which are all indispensable for higher linear and track density recording. View full abstract»

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  • Theory of rotational processes in perpendicular media and application to anisotropy measurement

    Page(s): 1902 - 1907
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    Numerical and analytical calculations of rotational processes in perpendicular recording media are presented. The work supports recent experimental studies that suggest that the measurement of rotational magnetization processes can be used to determine the value of the anisotropy constant. An expression for the rotational magnetization for a noninteracting system is derived taking into account the dispersion of K and the easy-axis orientation. The calculations show that the experiments determine the mean value of HK, essentially independent of the angular dispersion. A numerical (Monte-Carlo based) micromagnetic model is used to study the effects of magnetostatic and exchange interactions at nonzero temperatures. It is shown that for small values of KV/kT, irreversible magnetization processes take place, which preclude the use of the rotational magnetization method to determine K values. This effect is enhanced by the presence of the magnetostatic interaction. However, the presence of exchange interactions is found to enforce coherent rotation in small fields, reducing the irreversible processes and allowing the determination of HK. Under these circumstances, it is shown that the exchange does not significantly affect the value of HK, and that a well-defined demagnetization correction of 4πM is appropriate. Finally, a comparison with experimental data gives good agreement for multilayer and granular media and shows the role of domain formation on the rotational magnetization process. View full abstract»

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  • Approaches to tilted magnetic recording for extremely high areal density

    Page(s): 1930 - 1935
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    In this paper, we systematically present our fundamental understanding of the advantages of tilted magnetic recording. We investigate the various configurations of tilted magnetic recording including tilted longitudinal recording, tilted perpendicular recording with tilted media and normal single pole head, and tilted perpendicular recording with perpendicular media and tilted writing head. Tilted media with easy axis along the down-track and cross-track directions and tilted media with varied in-plane orientation ratios have been investigated and compared in detail. One important finding is that slightly oriented (in-plane) tilted media show a tremendous improvement in recording performance, which may release the pressure on the fabrication of perfect tilted hard disk magnetic media. Various fabrication methods for tilted media have also been discussed. View full abstract»

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  • Lessons from research of perpendicular magnetic recording

    Page(s): 1868 - 1870
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    Lessons from research of perpendicular magnetic recording are presented in this paper. The historical view of the developments in magnetic recording teaches us the "20-year rule" for technical developments and the "40-year rule" for technical evolutions. The research work in perpendicular magnetic recording also fruited with a new concept of classification of research work, which consists of three cyclic research models: creation, development, and integration. View full abstract»

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  • Conference author index

    Page(s): 1980
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IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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