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Magnetics, IEEE Transactions on

Issue 2 • Date Feb. 2005

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  • [Front cover]

    Page(s): c1
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  • IEEE Transactions on Magnetics publication information

    Page(s): c2
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  • Table of contents

    Page(s): 533 - 534
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  • TMRC 2004 Conference Committee

    Page(s): 536
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  • Composite media for perpendicular magnetic recording

    Page(s): 537 - 542
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    A composite perpendicular recording media consisting of magnetically hard and soft regions within each grain is proposed. Application of applied field initially causes the magnetization of the soft region to rotate and, thus, change the angle of the effective field applied to the hard region. This important change in the effective field is enabled by an exchange layer that moderates the interaction between the two regions. Energy arguments show that the resulting performance (as measured by the ratio of energy barrier to switching field) is similar to the previously proposed tilted media, while avoiding some of the difficulties. In particular, fabrication of the proposed composite media appears to be significantly easier than that of tilted media. View full abstract»

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  • Toward an understanding of grain-to-grain anisotropy field variation in thin film media

    Page(s): 543 - 548
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    Grain-to-grain anisotropy field variation has become one of the main causes of medium noise, especially in perpendicular thin film media. In this paper, we present an electron microscopy investigation and theoretical analysis on the grain-to-grain anisotropy field variation in various types of thin film recording media. In alloyed film media, the intrinsic grain-to-grain composition variation would present a lower limit on grain size, thereby limiting area recording density. It is also argued that partial ordering in L10 materials such as FePt would yield large anisotropy field variation, especially for low values of order parameter. View full abstract»

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  • High-density perpendicular recording media with large grain separation

    Page(s): 549 - 554
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    The possibility of 300-500 Gbit/in2 perpendicular recording using granular recording media has been investigated through micromagnetic simulation based on the Langevin equation. Writability and thermal stability in 10 years were obtained changing media parameters such as the grain size D, the grain separation d, and the thickness of the recording layer tmag for proper combination of the grain saturation magnetization Ms-grain and the grain perpendicular anisotropy energy Ku-grain. It was found that high-density recording is realized under the large grain separation, the large grain saturation magnetization, and the large grain anisotropy energy. The read/write calculation using ordered medium with D of 4.2 nm, d of 2.3 nm, tmag of 12.0 nm, Ms-grain of 1313 emu/cm3, and Ku-grain of 7.0 Merg/cm3 confirmed the possibility of 1303 kFCI and 1954 kFCI perpendicular recording, leading to 325 and 488 Gbit/in2 with 250 kTPI (track pitch of 102 nm). View full abstract»

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  • High-density perpendicular magnetic recording media of granular-type (FePt/MgO)/soft underlayer

    Page(s): 555 - 559
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    Perpendicular magnetic recording media, composed of granular-type FePt-MgO films on Fe-Ta-C soft magnetic underlayer (SUL), have been fabricated on to 2.5-in glass disks. [001] textured FePt granular films with high-perpendicular magnetic anisotropy were obtained by annealing the FePt/MgO multilayer films. The FePt grain size, perpendicular coercivity, magnetic activation volume, and the exchange coupling between the FePt grains were found to be strongly dependent on the initial multilayer structures and the annealing conditions. The recording performance of the disks was evaluated by a spin-stand. The obtained results reveal a close correlation between the recording performance and magnetic properties. The thermal stability of the granular-type FePt media was studied using high-temperature magnetic force microscopy (MFM) technique, equipped with in situ sample heating, in the temperature range 25°C-200°C. The estimated signal decay at high temperature is ascribed to the temperature dependent magnetic anisotropy behavior. View full abstract»

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  • High-anisotropy nanocluster films for high-density perpendicular recording

    Page(s): 560 - 565
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    This paper reports results on the synthesis and magnetic properties of L10:X nanocomposite films, where L10=FePt, CoPt, and X=C, Ag, etc. Two fabrication methods are discussed: nonepitaxial growth of oriented perpendicular media, and monodispersed nanoparticle-assembled films grown with a gas-aggregation source. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. The films show promise for development as recording media at extremely high areal densities. View full abstract»

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  • High-potential magnetic anisotropy of CoPtCr-SiO2 perpendicular recording media

    Page(s): 566 - 571
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    The magnetic anisotropy of CoPtCr-SiO2 perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy Ku at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches ∼15×106 erg/cm3. The addition of SiO2 to the CoPtCr films reduces the grain Ku, however the grain Ku maintains a large value of 8×106 erg/cm3 even when 10at%SiO2 is added to (Co90Cr10)80Pt20, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in2 revealed that the ratio of the high-energy anisotropy term Ku2 to Ku1(Ku=Ku1+Ku2) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small Ku2 values, however, the values of Ku1 and Ku2 vary significantly with the seed layer material used. Ku1 decreases almost linearly as the Ku2 value increases. It is concluded that CoPtCr films have a sufficient potential in the values of Ku1 and Ku2 for high-density perpendicular media. View full abstract»

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  • Very high-density and low-cost perpendicular magnetic recording media including new layer-structure "U-Mag"

    Page(s): 572 - 576
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    We have fabricated a new layered structure, named "U-mag," for perpendicular magnetic recording media, in terms of stacked films including a very thin (2 nm) ferromagnetic (Co) intermediate layer and lattice spacing control layers. The formed medium having a 100-nm soft magnetic underlayer with high coercivity over 6 kOe and sufficient nucleation field (-1.5 kOe) shows higher signal-to-noise ratio (SNR) than a medium with a conventional Ru underlayer. The detailed microstructures of the U-mag medium were also revealed by a transmission electron microscope with an energy dispersive spectrometer. A double Co intermediate layer gave a significant improvement in the SNR compared to a single Co layer. View full abstract»

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  • Exchange-biased soft underlayers for perpendicular recording

    Page(s): 577 - 580
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    We inserted NiFe/CoFe/antiferromagnetic-MnIr/CoFe layers between two CoTaZr soft layers to enhance the exchange-bias field (Heb) and then evaluated the effect of this lamination on the spike noise and recording characteristics of CoCrPt-SiOx media with an exchange-biased soft magnetic underlayer (SUL). The two CoTaZr layers were exchange-biased radially throughout the disk, and a higher Heb was obtained for the upper CoTaZr layer. By using the laminated SUL, spike noise was suppressed even when the total thickness of the CoTaZr layers was increased to 300 nm. Although the medium had a high Hc of 7.0 kOe, a fairly good overwrite and signal-to-noise ratio were obtained. As another application of exchange biasing, we also examined the possibility of combining exchange biasing and antiparallel-coupled (APC) soft layers; i.e., a pinned APC SUL. An exchange-bias field from the pinning layers to the lower CoTaZr layer and an exchange-coupled field between the two CoTaZr layers were successfully applied. The medium with the pinned APC SUL showed no spike noise throughout the disk, and wide-area adjacent track erasure was effectively suppressed. View full abstract»

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  • Preconditioning, write width, and recording properties of Co-Cr-Pt-O perpendicular media with various underlayer designs

    Page(s): 581 - 586
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    The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (tSUL) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (∼80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (∼50 nm) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for tSUL<100 nm. Comparable performance is achieved relative to media with tSUL∼150 nm. View full abstract»

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  • Recording performance characteristics of granular perpendicular media

    Page(s): 587 - 592
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    The recording performance of CoCrPtO granular-type perpendicular media was examined with two types of perpendicular heads to demonstrate the importance of matching head and media designs in perpendicular recording. Shielded-pole heads with high write field gradients, field angles, and sufficient write field magnitude yielded superior writability and signal-to-noise ratio as compared to mono-pole heads. The recording performance dependences on head-to-medium spacing, interlayer thickness, and soft-underlayer (SUL) thickness were also weaker with the shielded-pole heads. In addition, the effect of stray fields on the SUL domain noise was investigated for a synthetic antiferromagnetically-coupled (SAF) SUL. A radial field close to the exchange field of the SAF SUL was found to induce domain noises that could potentially cause errors in recording systems. View full abstract»

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  • Humidity effects in magnetic recording

    Page(s): 593 - 598
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    Humidity effects in magnetic recording are reviewed. We highlight the progress made toward quantifying water adsorption on lubricated overcoats, leading up to the present understanding of humidity effects on magnetic recording tribology. Recently, it was found that moisture is also absorbed by hygroscopic atmospheric contaminants to form liquid nanodroplets on the overcoat. Rheological and dielectric measurements were performed to investigate the properties of the nanodroplets. Solutions of 1 wt% to 10 wt% water in Ztetraol are gel like and highly viscous. Dissolved water increases the low-frequency permittivity and conductivity, and shortens the dielectric relaxation time, relative to dry lubricant. View full abstract»

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  • Self-assembled monolayers as lubricants for magnetic disk drives

    Page(s): 599 - 603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB) |  | HTML iconHTML  

    Self-assembled monolayers (SAMs) are an attractive alternative to perfluoropolyether (PFPE) lubricants because they have a strong adsorption to a solid surface and have the potential to overcome the limitations of PFPE, such as thermodynamic instability, nonuniformity, and spin off. In this paper, we describe the possibility of SAMs as lubricants (or as a component of a lubricant system) for magnetic disk drives. We also discuss a strongly bonded hydrocarbon film deposited on an amorphous carbon film using a vacuum vapor deposition technique. View full abstract»

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  • Modeling and simulation of hard-particle interaction in head/disk interfaces

    Page(s): 604 - 609
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    A hard particle interacting with a slider and a disk in the head/disk interface of hard-disk drives can produce a scratch on the disk and result in data loss. Our work emphasizes modeling and simulation of slider, particle, and disk interactions, scratch generating mechanisms, and linking of scratch to interface design parameters. Two models are presented. The Monte Carlo method was used to calculate scratch probabilities and parametric studies were performed to determine the effect on scratch probability of various parameters, such as friction coefficients, particle mean size, slider wall angles, the ion-milling (IM) etch depth from the air-bearing surface (ABS) of the slider, and the efficacy of additional ABS structures acting as particle shields. Simulation results show that the friction coefficient is a dominant parameter. If the disk friction coefficient is smaller than the slider friction coefficient, scratches are not produced. Using shallow IM depths is an effective and practical way to reduce the scratch probability. Experimental results are very close to the simulation predictions. View full abstract»

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  • Dynamics of sub-5-nm air-bearing sliders in the presence of electrostatic and intermolecular forces at the head-disk interface

    Page(s): 610 - 615
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    A head-disk interface (HDI) model has been used to investigate the effect of the intermolecular and electrostatic forces on the static and dynamic performance of air-bearing sliders. It is seen that the intermolecular and electrostatic forces increase the level of flying height modulations at low flying heights, which in turn results in dynamic instability of the system similar to what has also been observed in experiments. In the analysis a stiffness matrix is defined to characterize the stability in the vertical, pitch, and roll directions. Fly height diagrams are used to examine the multiple equilibriums that exist for low flying sliders. In addition, the simulation results are compared with previously published experiments for validation. View full abstract»

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  • The physics of disk lubricant in the continuum picture

    Page(s): 616 - 620
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    Molecular dynamics simulation would be well suited to predict the physics of molecularly-thick lubricants on magnetic disk surfaces. The difficulty in defining suitable interatomic potentials, as well as the requirement for large computing power, makes this type of study difficult. Treating the lubricant film in the framework of fluid dynamics has proven a much better way to model its behavior. This paper describes a full numerical model of lubricant moguls and ripples formation using finite difference analysis. We demonstrate that both moguls and ripples result from slider-induced air shear. Ripples tend to form at higher disk speed and narrower slider width, whereas moguls are seen at lower speed and larger slider width. Both moguls and ripples are enhanced for thicker lubricants, higher waviness, and lower flying heights. Ripple instabilities that were predicted earlier using a stability analysis are also quantitatively confirmed using this numerical model. View full abstract»

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  • ESCA-thickness metrology and head-medium spacing impact of disk lubricant

    Page(s): 621 - 625
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    Electron spectroscopy for chemical analysis (ESCA) has been commonly used as a metrology tool for lubricant film-thickness measurement on magnetic hard disks. The accuracy of the ESCA-thickness measurement rests solely with the calibration accuracy of the characteristic photoelectron attenuation length in the lubricant film. Several past studies on this subject yielded widely divergent results, due to the difficulty in obtaining an accurate, absolute lubricant film-thickness measurement. In this paper, we revisited the calibration issue and, instead of following the same paths pursued in the past, used a derivative method to yield an accurate calibration of the photoelectron attenuation length. We also compared the various methods for lubricant film-thickness calculation based on ESCA measurements and determined that the most accurate method is to use only the photoemission signal from the lubricant film. In addition, by studying the lubricant film-thickness effect on the electrical readback signal, we found that the lubricant film leads to an increase in the head-medium spacing by an amount greater than one times, but less than two times, its physical thickness. View full abstract»

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  • Will the numbers add up for sub-7-nm magnetic spacings? Future metrology issues for disk drive lubricants, overcoats, and topographies

    Page(s): 626 - 631
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB) |  | HTML iconHTML  

    To achieve disk drive recording densities greater than one terabit per square inch, future head-media spacings (HMSs) will need to be less than 7 nm. This will place severe demands on the metrology tools used to measure the thickness and topographies of the contributors to the head-media spacing. Here, we first review some of the metrologies used for characterizing overcoats, lubricants, and topographies and discuss some of the limits that will make it difficult to achieve a sub-7-nm HMS. We next show new results for measuring lubricant redistribution on disk surfaces after contact with a small pad on the slider and present a new method for determining wear rates of these slider contact pads. View full abstract»

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  • Effect of radial curvature of magnetic media on glide avalanche

    Page(s): 632 - 635
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    Spacing loss due to micro-waviness and curvature effects in the radial direction of a disk was investigated via numerical simulations and measurements. New techniques based on interferometry and laser scanning were employed to measure radius of curvature (ROC) and to reconstruct the profiles at the outer edge of a disk. A good correlation between ROC values and fly height degradation was obtained, and ROC less than 50 m clearly showed the deterioration in fly height by as much as 1.5 nm. The new measurement techniques proved to be an important means to improve substrate manufacturing processes. View full abstract»

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  • Synthetic ferrimagnetic media: effects of thermally assisted writing

    Page(s): 636 - 641
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    Thermally assisted writing on high-coercivity synthetic ferrimagnetic media (SFM) was demonstrated using a conventional spin stand equipped with an optical head for commercial magnetooptical drives. The laser light (λ = 685 nm) was focused through a glass substrate onto a recording layer. The optical spot size was 1.1 μm and a commercial magnetic head had a writer width of ∼0.25 μm. The recording properties were measured as a function of the writing current (Iw) and the laser power (Pw). For the thermally stable medium with Hc = 6 kOe, a laser irradiation with an optimum power significantly improved the overwrite performance and the signal-to-noise ratio (SNR) values. The SNR values were improved by optimizing Pw over a wide writing current range. The improvements with the assist were found in both the signal and the noise. The media with a large dynamic coercivity value or with thick magnetic layers clearly showed the advantages with thermal assist. View full abstract»

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  • Laminated antiferromagnetically coupled media - optimization and extendibility

    Page(s): 642 - 647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    Lamination of multiple isolated magnetic layers has been shown to be an effective method to significantly increase signal-to-noise ratio in longitudinal media. These laminated media, however, are accompanied by low overwrite and wide magnetic pulse width, mainly as a result of poor writing of the bit transitions in the magnetic layer further away from the head and an offset in the transition position in the multiple magnetic layers resulting from head field spacing loss. We have demonstrated that the transition writing and transition alignment in the multiple magnetic layers of the laminated antiferromagnetically coupled (AFC) media can be optimized by adjusting the magnetic anisotropy of the relevant magnetic layers to compensate for the reduction of the head field magnitude with spacing. Such optimization results in significant improvements in media recording performance, leading to successful application of this medium technology. In this paper, we will highlight some of these improvements and discuss our approaches to further improve the recording performance by reducing the thicknesses of the magnetic layers and the lamination spacer layer in the laminated AFC film stack and by introducing additional elements in the magnetic layer. View full abstract»

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Aims & Scope

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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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology