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Yoshiaki Sonobe - One of the best experts on this subject based on the ideXlab platform.

  • Reverse dc erase Medium noise analysis on exchange-coupling effect in coupled granular/continuous Perpendicular recording media
    Journal of Applied Physics, 2003
    Co-Authors: Yoshiaki Sonobe, Yoshihiro Ikeda, Hiroaki Muraoka, B.k. Yen, Kentaro Takano, Hoa Van, Natacha F. Supper, Yoshihisa Nakamura
    Abstract:

    The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) Perpendicular Medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the Medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupli...

  • Pinning of written bits in Perpendicular recording media
    Journal of Magnetism and Magnetic Materials, 2001
    Co-Authors: Simon John Greaves, Yoshiaki Sonobe, Hiroaki Muraoka, Manfred Ernst Schabes, Yoshihisa Nakamura
    Abstract:

    A Perpendicular Medium comprising two distinct magnetic layers is described. One layer has a granular structure with isolated, exchange-decoupled grains and the other is a continuous, exchange-coupled layer. In the combined structure domain wall movement is restricted and reversed grains within written bits are eliminated. The S/N ratio is improved compared with single layers of either type alone.

  • Medium noise and grain size analysis of cocrpt ti Perpendicular media with nial seed layer
    IEEE Transactions on Magnetics, 2001
    Co-Authors: Y Ikeda, Yoshiaki Sonobe, Gabriel Zeltzer, B.k. Yen, Kentaro Takano, Eric E Fullerton, Philip M. Rice
    Abstract:

    Perpendicular Medium with an average grain size of 8.2 nm have been produced by using a-CoCrPt/Ti/NiAl tri-layer structure. The signal-to-noise ratio for the tri-layer Medium is 2-7 dB higher than CoCrPt/Ti bi-layer Medium at low deposition temperatures. The Medium noise is dominated by dc noise and exhibits little transition noise for densities less than 500 kFCI. The ultra-small grain size will improve the performance of Perpendicular media for future high-density recording applications.

  • Microstructure study of CoCrPt/Ti/NiAl Perpendicular media
    Journal of Magnetism and Magnetic Materials, 2001
    Co-Authors: Yoshihiro Ikeda, Yoshiaki Sonobe, Gabriel Zeltzer, B.k. Yen, Kentaro Takano, Hoa Van, Philip M. Rice
    Abstract:

    Perpendicular Medium with an average grain size of 8.2 nm with 20 nm thickness has been produced by using a-CoCrPt/Ti/NiAl tri-layer structure. The signal-to-noise ratio improves with the addition of a NiAl seed layer. From the TEM image analysis, the introduction of the NiAl seed layer may enhance the separation between the CoCrPt grains. The ultra-small grain size will improve the performance of Perpendicular media for future high-density recording applications.

  • Characterization of a thick CoCr Perpendicular Medium for a merged MR head
    Journal of Magnetism and Magnetic Materials, 1997
    Co-Authors: Yoshihiro Ikeda, Yoshiaki Sonobe, Hiroshi Uchida, T Toyooka
    Abstract:

    Abstract We have been studying a single-layer CoCr Perpendicular Medium with a thickness of 100–700 nm, using a merged MR head designed for longitudinal recording. The Co 78 Cr 22 Medium shows good linearity in its output dependence on the MR bias current. The output is 50% larger than that for a longitudinal Medium. A maximum D 50 value of 100 kFCI was obtained for a Medium with an optimum thickness of 300 nm. The Medium noise increases with the Medium thickness, whereas the output saturates at 300 nm. The thick Medium has two demerits: large write demagnetization and a high level of Medium noise. Increasing the Cr content of the CoCr Medium from 22 to 28 at% significantly reduces these two problems. Cr-rich Perpendicular media with thicknesses of over 100 nm are expected to replace longitudinal media in hard disk drives in the near future.

Yoshihisa Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • Reproduced waveform and bit error rate analysis of a patterned Perpendicular Medium R/W channel
    Journal of Applied Physics, 2005
    Co-Authors: Yoshio Suzuki, Hajime Aoi, Hiroaki Muraoka, H. Saito, Yoshihisa Nakamura
    Abstract:

    Patterned media were investigated as candidates for 1Tb∕in.2 recording. In the case of recording with a patterned Medium, the noise due to the irregularity of the pattern has to be taken into account instead of the Medium noise due to grains. The bit error rate was studied for both continuous and patterned media to evaluate the advantages of patterning. The bit aspect ratio (BPI/TPI) was set to two for the patterned media and four for the continuous Medium. The bit error rate (BER), calculated with a PR(1,1) channel simulator, indicated that for both double layered and single layered patterned media an improvement of the BER over conventional continuous media is expected when the patterning jitter is controlled to within 8%. When the system noise is large the BER of single layered patterned media deteriorates more rapidly than that of double layered media, due to the higher boost in the PR(1,1) channel. It was found that making the land length to bit length ratio large was quite effective at improving BER.

  • Reverse dc erase Medium noise analysis on exchange-coupling effect in coupled granular/continuous Perpendicular recording media
    Journal of Applied Physics, 2003
    Co-Authors: Yoshiaki Sonobe, Yoshihiro Ikeda, Hiroaki Muraoka, B.k. Yen, Kentaro Takano, Hoa Van, Natacha F. Supper, Yoshihisa Nakamura
    Abstract:

    The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) Perpendicular Medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the Medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupli...

  • A study of turbo decoding with embedded AR channel model for Perpendicular recording
    IEEE Transactions on Magnetics, 2003
    Co-Authors: Yoshihisa Nakamura, Yoshihiro Okamoto, Hisashi Osawa, Hidetoshi Saito, Hiroaki Muraoka
    Abstract:

    Turbo decoding with an embedded autoregressive (AR) channel model is studied in an actual Perpendicular magnetic recording channel. Performance of the a posteriori probability (APP) decoder is improved by applying an AR channel model in order to estimate the decoder input sequence. The bit-error-rate (BER) performance is obtained by read/write experiments using a spin stand with a Perpendicular Medium and an single-pole-type/giant magnetoresistive (SPT/GMR) head. The results show that our turbo coding and iterative decoding system using an AR channel model improves the BER performance.

  • Pinning of written bits in Perpendicular recording media
    Journal of Magnetism and Magnetic Materials, 2001
    Co-Authors: Simon John Greaves, Yoshiaki Sonobe, Hiroaki Muraoka, Manfred Ernst Schabes, Yoshihisa Nakamura
    Abstract:

    A Perpendicular Medium comprising two distinct magnetic layers is described. One layer has a granular structure with isolated, exchange-decoupled grains and the other is a continuous, exchange-coupled layer. In the combined structure domain wall movement is restricted and reversed grains within written bits are eliminated. The S/N ratio is improved compared with single layers of either type alone.

  • Simplified expression of shielded MR head response for double-layer Perpendicular Medium
    IEEE Transactions on Magnetics, 1999
    Co-Authors: Hiroaki Muraoka, Y. Sugita, Yoshihisa Nakamura
    Abstract:

    An approximated simple expression of MR head response was given for Perpendicular double-layer media. The equation was derived by modifying Fan's equation so as to be of a nonintegral form. The validity was confirmed by comparisons with exact solutions of the Fan's equation, which resulted in errors of less than 10% for practical applications of recent MR heads. Using the expression, the reciprocity theorem revealed that the measured transition length of Perpendicular recording was extremely small, less than 10 nm.

Hiroaki Muraoka - One of the best experts on this subject based on the ideXlab platform.

  • Reproduced waveform and bit error rate analysis of a patterned Perpendicular Medium R/W channel
    Journal of Applied Physics, 2005
    Co-Authors: Yoshio Suzuki, Hajime Aoi, Hiroaki Muraoka, H. Saito, Yoshihisa Nakamura
    Abstract:

    Patterned media were investigated as candidates for 1Tb∕in.2 recording. In the case of recording with a patterned Medium, the noise due to the irregularity of the pattern has to be taken into account instead of the Medium noise due to grains. The bit error rate was studied for both continuous and patterned media to evaluate the advantages of patterning. The bit aspect ratio (BPI/TPI) was set to two for the patterned media and four for the continuous Medium. The bit error rate (BER), calculated with a PR(1,1) channel simulator, indicated that for both double layered and single layered patterned media an improvement of the BER over conventional continuous media is expected when the patterning jitter is controlled to within 8%. When the system noise is large the BER of single layered patterned media deteriorates more rapidly than that of double layered media, due to the higher boost in the PR(1,1) channel. It was found that making the land length to bit length ratio large was quite effective at improving BER.

  • Performance comparison of post-processor for PRML channel in Perpendicular magnetic recording
    Journal of Magnetism and Magnetic Materials, 2005
    Co-Authors: Yasuaki Nakamura, Yoshihiro Okamoto, Hisashi Osawa, Hiroaki Muraoka
    Abstract:

    Abstract In this paper, post-processors for the partial-response maximum-likelihood (PRML) channel combined with the Reed–Solomon (RS) encoder/decoder are studied in Perpendicular magnetic recording. The bit error rate (BER) performance is obtained by read/write experiments using a spin-stand with a Perpendicular Medium and single-pole-type/giant magnetoresistive (SPT/GMR) head. The experimental results show that post-processors improve linear densities of about 10–20 kBPI in Perpendicular magnetic recording.

  • Reverse dc erase Medium noise analysis on exchange-coupling effect in coupled granular/continuous Perpendicular recording media
    Journal of Applied Physics, 2003
    Co-Authors: Yoshiaki Sonobe, Yoshihiro Ikeda, Hiroaki Muraoka, B.k. Yen, Kentaro Takano, Hoa Van, Natacha F. Supper, Yoshihisa Nakamura
    Abstract:

    The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) Perpendicular Medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the Medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupli...

  • A study of turbo decoding with embedded AR channel model for Perpendicular recording
    IEEE Transactions on Magnetics, 2003
    Co-Authors: Yoshihisa Nakamura, Yoshihiro Okamoto, Hisashi Osawa, Hidetoshi Saito, Hiroaki Muraoka
    Abstract:

    Turbo decoding with an embedded autoregressive (AR) channel model is studied in an actual Perpendicular magnetic recording channel. Performance of the a posteriori probability (APP) decoder is improved by applying an AR channel model in order to estimate the decoder input sequence. The bit-error-rate (BER) performance is obtained by read/write experiments using a spin stand with a Perpendicular Medium and an single-pole-type/giant magnetoresistive (SPT/GMR) head. The results show that our turbo coding and iterative decoding system using an AR channel model improves the BER performance.

  • Pinning of written bits in Perpendicular recording media
    Journal of Magnetism and Magnetic Materials, 2001
    Co-Authors: Simon John Greaves, Yoshiaki Sonobe, Hiroaki Muraoka, Manfred Ernst Schabes, Yoshihisa Nakamura
    Abstract:

    A Perpendicular Medium comprising two distinct magnetic layers is described. One layer has a granular structure with isolated, exchange-decoupled grains and the other is a continuous, exchange-coupled layer. In the combined structure domain wall movement is restricted and reversed grains within written bits are eliminated. The S/N ratio is improved compared with single layers of either type alone.

T Toyooka - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of a thick CoCr Perpendicular Medium for a merged MR head
    Journal of Magnetism and Magnetic Materials, 1997
    Co-Authors: Yoshihiro Ikeda, Yoshiaki Sonobe, Hiroshi Uchida, T Toyooka
    Abstract:

    Abstract We have been studying a single-layer CoCr Perpendicular Medium with a thickness of 100–700 nm, using a merged MR head designed for longitudinal recording. The Co 78 Cr 22 Medium shows good linearity in its output dependence on the MR bias current. The output is 50% larger than that for a longitudinal Medium. A maximum D 50 value of 100 kFCI was obtained for a Medium with an optimum thickness of 300 nm. The Medium noise increases with the Medium thickness, whereas the output saturates at 300 nm. The thick Medium has two demerits: large write demagnetization and a high level of Medium noise. Increasing the Cr content of the CoCr Medium from 22 to 28 at% significantly reduces these two problems. Cr-rich Perpendicular media with thicknesses of over 100 nm are expected to replace longitudinal media in hard disk drives in the near future.

  • High Signal-to-noise Ratio Of A Cr-Rich CoCrPt Perpendicular Medium With A Large Medium Thickness
    IEEE Transactions on Magnetics, 1997
    Co-Authors: Yoshihiro Ikeda, Hiroshi Uchida, Y. Sonobe, T Toyooka
    Abstract:

    A Cr-rich (Co/sub 72/Cr/sub 28/)/sub 94/Pt/sub 6/ Perpendicular Medium with a large thickness of 300 nm, integrated with an MR head designed for longitudinal recording, achieved a high signal-to-noise ratio of 37 dB at 100 kFCI and a D/sub 50/ of 150 kFCI. A high Pt content of 17-22 at.% is effective for increasing the Hk value and signal amplitude at 10 kFCI, and for decreasing the write demagnetization. However, it also decreases the S/N at 100 kFCI and the D/sub 50/. The signal amplitude rapidly increases with the Pt content from 0 to 6 at.%, and saturates at around 6 at.%. This contributes to the high S/N obtained at a Pt content of 6-11 at.%. Compared with a longitudinal Medium optimized for the same MR head, the proposed Medium has a 2 dB higher S/N at 100 kFCI, a 1.3 times larger D/sub 50/, and a 1.5 times larger signal amplitude at 10 kFCI. The thickness of the Medium will contribute to the thermal stability of magnetic bits at future high recording density of 10 Gbits/in/sup 2/ and beyond.

  • Novel composite Perpendicular recording Medium with Co/sub 78/Cr/sub 22/ over Cr-rich Co/sub 72/Cr/sub 28/ for merged MR heads
    IEEE Transactions on Magnetics, 1997
    Co-Authors: Yoshiaki Sonobe, Hiroshi Uchida, T Toyooka, Yoshihiro Ikeda, Y. Tagashira
    Abstract:

    We propose a new type of composite Perpendicular Medium consisting of a 50-nm-thick Co/sub 78/Cr/sub 22/ upper layer and a 50-nm-thick Cr-rich Co/sub 72/Cr/sub 28/ lower layer for magnetic recording systems using MR heads. The lower Cr-rich layer, with strong magnetic interaction in the Perpendicular direction and good crystalline orientation, contributes to the high resolution and high signal-to-noise ratio (S/N). The upper layer, with large saturation magnetization (M/sub s/) and large anisotropy field (H/sub kl/), plays a major role in increasing the signal amplitude. Magnetic recording characterization using this Medium and a merged MR head yielded a D/sub 50/ of 140 kFCI, an S/N of 33.4 dB, and a signal amplitude of 411 /spl mu/V/sub pp/ at 100 kFCI with a 62-nm magnetic spacing.

  • noise and spl delta m spl perp analysis of a cr rich co cr Perpendicular Medium for an mr head
    IEEE Transactions on Magnetics, 1996
    Co-Authors: Y Ikeda, Yoshiaki Sonobe, Hiroshi Uchida, T Toyooka
    Abstract:

    The Medium noise in a Cr-rich Co-Cr alloy Perpendicular Medium was investigated by using an MR head designed for longitudinal recording. Medium with a Cr content of 28 at.% showed a high crystalline orientation and a low write-demagnetization effect. The signal-to-noise ratio (S/N) of the Medium was higher than that of conventional Co-Cr Perpendicular media for inductive heads. The advantages of the Medium derive from the large inter-particle Perpendicular magnetic interaction (/spl Delta/M/spl perp/) of media, which increased linearly with the Cr content, reaching a maximum value at 28 at.%. This strong interaction in the Medium results in a high S/N for a recording system using a single-layer Perpendicular Medium and an MR head.

  • Noise and /spl Delta/M/spl perp/ analysis of a Cr-rich Co-Cr Perpendicular Medium for an MR head
    IEEE Transactions on Magnetics, 1996
    Co-Authors: Y Ikeda, Yoshiaki Sonobe, Hiroshi Uchida, T Toyooka
    Abstract:

    The Medium noise in a Cr-rich Co-Cr alloy Perpendicular Medium was investigated by using an MR head designed for longitudinal recording. Medium with a Cr content of 28 at.% showed a high crystalline orientation and a low write-demagnetization effect. The signal-to-noise ratio (S/N) of the Medium was higher than that of conventional Co-Cr Perpendicular media for inductive heads. The advantages of the Medium derive from the large inter-particle Perpendicular magnetic interaction (/spl Delta/M/spl perp/) of media, which increased linearly with the Cr content, reaching a maximum value at 28 at.%. This strong interaction in the Medium results in a high S/N for a recording system using a single-layer Perpendicular Medium and an MR head.

Jian-gang Zhu - One of the best experts on this subject based on the ideXlab platform.

  • Domain Wall Pinning and Corresponding Energy Barrier in Percolated Perpendicular Medium
    IEEE Transactions on Magnetics, 2007
    Co-Authors: Yuhui Tang, Jian-gang Zhu
    Abstract:

    The domain wall pinning processes in a percolated Perpendicular Medium are studied using micromagnetic modeling. With a given nonmagnetic pinning site, the energy barrier of the pinned domain wall reaches a maximum when the domain wall width is about twice the size of the pinning site. For transitions in the percolated Perpendicular Medium, the energy barrier for the transition shift is sensitive to the pinning site spacing. Considering regularly distributed pinning sites with 4.7-nm center-to-center spacing, the energy barrier for the transition shift is about twice the energy barrier of the domain wall pinned by one pinning site. The domain stability in percolated Perpendicular Medium is also discussed with an analytic model

  • micromagnetics of percolated Perpendicular Medium for 1 tb in 2 and beyond
    IEEE Transactions on Magnetics, 2006
    Co-Authors: Yuhui Tang, Jian-gang Zhu
    Abstract:

    A fully exchange coupled Perpendicular Medium with densely distributed nonmagnetic pinning sites has been proposed. In the novel microstructure configuration, the dense domain wall pinning sites enable the Perpendicular Medium to obtain narrow transitions and small transition noise. Using the micromagnetic modeling, the macromagnetic properties and recording performances of the novel Medium have been investigated. The results show that the Medium transition noise can be optimized with a moderate exchange coupling constant. The dynamic recording processes are studied with different damping constants and recording field amplitudes. Our study indicates that the switching time of the percolated Medium is smaller than 1 ns even with low switching field and small damping constant

  • a Medium microstructure for high area density Perpendicular recording
    Journal of Applied Physics, 2006
    Co-Authors: Jian-gang Zhu, Yuhui Tang
    Abstract:

    A Perpendicular Medium microstructure consisting of fully exchange coupled grains with densely distributed nonmagnetic pinning sites, referred to as the percolated Perpendicular Medium, is proposed. In this Medium, the ferromagnetic exchange coupling between the grains ensures sufficient thermal stability, while the densely distributed domain wall pinning sites ensure relatively smooth transition boundaries. The detailed magnetic hysteresis properties and recording characteristics of the percolated Perpendicular media are investigated via micromagnetic modeling. The study found that the percolated Medium could offer much improved recording properties in terms of enhanced transition sharpness and reduced transition noise while maintaining thermal stability in comparison to present granular Perpendicular Medium.

  • Micromagnetics of Percolated Perpendicular Medium for 1 Tb/in $^2$ and Beyond
    IEEE Transactions on Magnetics, 2006
    Co-Authors: Yuhui Tang, Jian-gang Zhu
    Abstract:

    A fully exchange coupled Perpendicular Medium with densely distributed nonmagnetic pinning sites has been proposed. In the novel microstructure configuration, the dense domain wall pinning sites enable the Perpendicular Medium to obtain narrow transitions and small transition noise. Using the micromagnetic modeling, the macromagnetic properties and recording performances of the novel Medium have been investigated. The results show that the Medium transition noise can be optimized with a moderate exchange coupling constant. The dynamic recording processes are studied with different damping constants and recording field amplitudes. Our study indicates that the switching time of the percolated Medium is smaller than 1 ns even with low switching field and small damping constant

  • Experimental study of overwrite mechanism in Perpendicular recording
    IEEE Transactions on Magnetics, 2005
    Co-Authors: Jian-gang Zhu, Yuchen Zhou
    Abstract:

    In this paper, we present an experimental study of the overwrite mechanism in Perpendicular recording, utilizing a scanning contact recording tester. It is found when writing new data over existing old data in a Stoner-Wohlfarth like Perpendicular Medium, the on-track remanence level (the regions between two adjacent transitions) of the new transitions is modulated by the old data pattern. This is because of the relatively poorer effective write field in the middle of the pole-tip footprint. It is argued that the demagnetization field from the residual magnetization pattern underneath the middle of the pole-tip region significantly affects the writing at the trailing edge, resulting in the observed modulation The phenomenon becomes less pronounced when the magnetic reversal becomes less dependent on the field angle.