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Magnetics, IEEE Transactions on

Issue 11  Part 2 • Date Nov. 2008

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Displaying Results 1 - 25 of 308
  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 3325 - 3359
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    Freely Available from IEEE
  • Monolithically Fabricated Hybrid Head for Near-Field Assisted Magnetic Recording

    Page(s): 3360 - 3363
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1375 KB) |  | HTML iconHTML  

    In this paper, we show a monolithically fabricated hybrid head with a GaAs-based laser diode capable of near-field-assisted magnetic recording. A bottlenecked conductor was placed beside the laser cavity formed on the trailing side of the head. The bottlenecked structure is used as a generator of magnetic and near fields. The structure consists of a couple of opposite electrodes with a 200-nm gap and a bridge connection between the electrodes. The magnetic field is mainly generated around the bottleneck by feeding current through the conductor. The near field is produced along edges of the bottleneck by irradiating a laser beam. We confirmed the 3-D localization of near field in the nanometer size around the bottleneck by means of a near-field scanning optical microscope. We attained the nanosized overlap between magnetic filed and near-field distributions on the hybrid head with the laser diode. View full abstract»

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  • Design, Fabrication, and Characterization of Near-Field Apertures for 1 Tbit/in ^{2} Areal Density

    Page(s): 3364 - 3367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (735 KB) |  | HTML iconHTML  

    Today, conventional magnetic recording schemes are coming to an end because of the superparamagnetic limit. Heat-assisted magnetic recording (HAMR) may ultimately extend data densities beyond 1 TB/in2. HAMR systems utilize the phenomenon during which the magnetic properties of the recording media could be locally modified via heating (optionally, by an optical source in the near field) to temperature in the vicinity of the Curie value of the media material. As a result, heat induced by the optical source can temporarily reduce the magnetic coercivity of high anisotropy material to a level attainable by the magnetic writing head, thus making it feasible to record on relatively small ultra-high anisotropy (and thermally stable) grains, consequently enhancing the areal density dramatically. The key challenge is to develop a near-field transducer capable of delivering over 50 nW into a spot diameter of 30 nm. Traditional fiber schemes are barely capable of 0.1 nW. To resolve the issue, a laser diode could be placed with the emitting edge only a few nanometers away from the recording media. The light can propagate through a nanoaperture on the surface of an aluminum-coated emitting edge. This paper will present an experimental study of recording characteristics of various near-field transducers fabricated via focused ion beam (FIB). To count the number of photons emitted in the near field, a scanning near-field optical microscopy system has been implemented. The experiments indicate that the FIB-fabricated transducers could deliver power of over a few microwatt into a 30-nm spot (Fig. 7). View full abstract»

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  • Magnetic Properties of Amorphous Magnetic Film on Self-Assembled Convex Pattern

    Page(s): 3368 - 3371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1200 KB) |  | HTML iconHTML  

    In this paper, we evaluated magnetic properties of amorphous Tb-Fe-Co magnetic film on self-assembled convex pattern fabricated using conventional sputtering and reactive ion etching equipments. Fabricated pattern had 2-D periodicity of around 28 nm. Tb-Fe-Co film on the pattern indicated that the domain-wall (DW) energy was reduced at the steep region of the pattern, and magnetic reversal behavior became more like Stoner-Wohlfarth mode than DW motion mode. Magnetic force microscope observation showed the magnetic domain whose sizes are as small as 50 nm. View full abstract»

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  • Application of Circularly Polarized Plasmon Resonance Modes to All-Optical Magnetic Recording

    Page(s): 3372 - 3375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    The numerical study of circularly polarized plasmon resonance modes in metallic nanoparticles with uniaxial symmetry is reported. These plasmon modes provide optical means for nanoscale focusing of circularly polarized light. For this reason, these modes are promising for all-optical magnetization reversals of nanoscale spots of magnetic recording media. A general theoretical approach to the analysis of circularly polarized plasmon modes is presented and then applied to two specific designs of silver nano-rings and spherical nanoshells on dielectric substrates. View full abstract»

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  • Narrow Track Confinement by AC Field Generation Layer in Microwave Assisted Magnetic Recording

    Page(s): 3376 - 3379
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB) |  | HTML iconHTML  

    Microwave assisted magnetic recording (MAMR) has been proposed to provide sufficient writability in magnetic recording when the magnetic grain has a large crystalline anisotropy field in high recording density. In this paper, the relationship between the track width and recording head designs in this novel recording scheme is studied using micromagnetic modeling. By controlling the AC field generation layer width, high track density can be obtained without decreasing the main pole width in the writer. A quantitive result shows 770 KTPI can be realized in MAMR with a 120 nm wide main pole and 25 nm wide AC field generation layer. View full abstract»

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  • Compositional Dependence of g-Factor and Damping Constant of GdFeCo Amorphous Alloy Films

    Page(s): 3380 - 3383
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (122 KB) |  | HTML iconHTML  

    Time-domain magnetization dynamics of sputtered GdFeCo (30 nm) amorphous alloy films was measured by pump-probe method using high-power ultra-short pulse fiber laser. The effective g-factor g eff and effective damping constant alphaeff of the GdFeCo films were estimated by using a numerical calculation of Landau-Lifshitz-Gilbert equation. The precessional frequency took a maximum near the magnetization compensation composition C M of the GdFeCo, while the estimated g eff and alphaeff increased around the angular momentum compensation composition C A. The compositional dependences of g eff and alphaeff were roughly described by a mean-field model. The g eff and alphaeff were also estimated from the ferromagnetic resonance (FMR) spectra, and the data from the FMR spectra agreed well with those from the pump-probe measurement except for the composition near C M. The FMR method was unable to excite the magnetization near C M because of the small net magnetization. View full abstract»

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  • A Simple Model for Optimal Read Width Due to Finite Write Width and Offtrack Interference

    Page(s): 3384 - 3387
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB) |  | HTML iconHTML  

    With increasing recording areal density, the read width needs to be continuously reduced. For a given density, a narrower reader is preferred because of the reduced side reading from residual old information and adjacent tracks. On the other hand, for the written track, better crosstrack averaging and, thus, a higher signal-to-noise ratio (SNR) comes with a wider reader. As a result, an optimal read width exists for a certain recording system. In this paper, a simple estimate of SNR is presented that includes the effect of the finite widths of the reader, the written track, as well as the offtrack interference. The optimal read width is obtained by maximizing the SNR value with a different read width. The effect of read width on offtrack capability, SNR to written track width sensitivity, and the impact of the shape of the microtrack profile will also be discussed. A comparison with an experiment shows good agreement between measurements and calculations. View full abstract»

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  • Micromagnetic Study of Short and Long Yoke PMR Head With Trailing Shield

    Page(s): 3388 - 3391
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    The response of a trailing shielded perpendicular magnetic recording (PMR) write head with a three-turn two-layer coils is calculated using a full micromagnetic large scale model including return pole and soft underlayer. We study the effect of PMR yoke length and write current overshoot on the dynamic response of the head at high frequency. In particular, recording performance parameter, nonlinear transition shift (NLTS) is simulated using micromagnetic media model. Shorter yoke length head improves NLTS as compared with longer yoke length. Measured NLTS has qualitative agreement with micromagnetic model results. View full abstract»

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  • Reduction in Switching Field for a Granular Perpendicular Medium Using Microwave Assisted Magnetic Recording

    Page(s): 3392 - 3395
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB) |  | HTML iconHTML  

    This paper describes the basic physics of magnetization switching in the presence of a dc bias and an in-plane radio-frequency (RF) field using a micromagnetic model based on the Landau-Lifshitz-Gilbert formulation for the magnetization dynamics. We start with the case of a uniform granular media at T = 0 K without any distributions in grains or medium properties. The switching behavior of this medium is essentially the same as that of a single grain and can be described by replacing HK of the grain with H'K = HK- 4piMs of the medium. Significantly smaller values of the dc bias field compared to the Stoner-Wohlfarth field are needed to reverse the medium for the assumed medium properties at low damping constant alpha. This reduction in dc bias field is progressively less at higher values of damping constant. However, increasing RF field magnitude can provide a significant reduction in the dc bias field even for high alpha values. As grain size distributions are added, the coherent precession of the medium grains can be sustained only for very short duration due to varying self-demagnetization of individual grains. Once the coherent precession is lost, a higher dc bias field compared to the case of uniform granular medium is required to completely reverse all the grains in the medium. At finite temperature and with the inclusion of grain size and magnetic materials distributions, the coherent precession is completely lost, thereby requiring even larger dc bias field for complete reversal of the grains. However, this dc bias field is still significantly smaller compared to the dc field required without the presence of RF field. The need for smaller dc bias field may mitigate the writeability requirements for high areal density recording. View full abstract»

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  • A Trailing Shield Perpendicular Writer Design With Tapered Write Gap for High Density Recording

    Page(s): 3396 - 3399
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    With the continuous push for high areal density, the conventional trailing shield perpendicular writer design faces an increasing challenge in maintaining sufficient writability while scaling down the dimensions of the write pole and the shield. In this work, we investigate an improved trailing shield design with the tapered write gap (TWG). It has been found that the TWG design has two unique recording characteristics that enable better extendibility: 1) flux concentration and 2) self-compensation. Both modeling and experimental results show that the TWG design has superior dynamic performance (DP) than conventional trailing shield design, while the sigma of DP parameters induced by the wafer/back-end variations is reduced. View full abstract»

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  • Effect of Interlayer on Read Write Processes in Perpendicular Recording

    Page(s): 3400 - 3403
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    The interlayer in perpendicular recording affects the distance between the head and the soft underlayer (SUL, or keeper) and thus plays an important role in overall recording performance. We investigate the effect of interlayer thickness on read write processes in perpendicular recording. We show that different media designs lead to different responses during the write process. On the other hand, the effect of the interlayer thickness on the read-back process is more complicated; reducing the interlayer thickness may not necessarily lead to better performance. View full abstract»

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  • Influence of Negative Field on Media Noise in Combinations of Capped Medium and Shielded Pole Heads

    Page(s): 3404 - 3407
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (509 KB) |  | HTML iconHTML  

    In this study, a new mechanism responsible for the increase in media noise in perpendicular magnetic recording is discussed. We observed that the media noise of a particular linear density drastically increased for some combinations of shielded pole heads and capped media with higher Ms of cap layers and thinner SUL. A MFM observation indicated that the transition jitter increased at a linear density, which correlated with the domain width in the AC-erased region. It was assumed that the reconstruction of the magnetic domains due to the negative field around the trailing shield occurred when the transition period was comparable to the magnetic cluster size. These results indicated that the optimization of the field at the edge of the trailing shield and that of the magnetic characteristics for the cap layer were important for improving the overall R/W performance. View full abstract»

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  • Investigation on Magnetic Fields From Field-Generating Layer in MAMR

    Page(s): 3408 - 3411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (634 KB) |  | HTML iconHTML  

    Microwave-assisted magnetic recording (MAMR) has recently emerged as a candidate to solve the trilemma in magnetic recording. In this study, the fundamental characteristics of the magnetic fields generated by a field-generating layer (FGL) are investigated using micromagnetic simulations. The relationships between the fields generated by the FGL and magnetic parameters, such as interlayer exchange coupling strength (Aperp) and the anisotropy constant (K), are investigated. In addition, oscillation behaviors are investigated by examining the magnetization configurations of the FGL. A Bloch-line-like magnetic structure is observed in the FGL in the stable oscillation mode. The Bloch-line-like structure functions as a rotation axis. However, it disappears in the unstable oscillation mode. View full abstract»

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  • Effect of Media Reversal Mode on Head Footprint

    Page(s): 3412 - 3415
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    Using a ldquodragrdquo tester in which the recording head is in direct contact with a perpendicular media disc, we show experimentally that the footprint of the head has a ldquodoughnutrdquo shape, as predicted by theory. A change in the switching properties of the media, from coherent rotation in conventional perpendicular media to incoherent rotation in exchange spring media, can be detected through the transformation of the head footprint, from ldquodoughnutrdquo to a dome-like shape. View full abstract»

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  • Feasibility of Perpendicular Magnetic Printing at 1 Tb/in ^{2}

    Page(s): 3416 - 3418
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    The feasibility of perpendicular magnetic printing for ultrahigh-density hard disks (HDs) was investigated by using the micromagnetic simulation. Our results suggest that the exchange constant dependence of the printing performance has a maximum value and the applied printing field should be less than the coercivity. Although the printing performance slightly deteriorates as the recording density increases, the printing performance is expected to be kept 70% at 1 Tb/in2 . Therefore, it was clarified that the perpendicular magnetic printing is feasible even at ultrahigh density such as 1 Tb/in 2. View full abstract»

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  • Overwrite Induced Divergent Transition by Trapezoid Pole Head

    Page(s): 3419 - 3422
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (497 KB) |  | HTML iconHTML  

    Perpendicular magnetic recording has to use a trapezoid writing pole in order not to enlarge the width of the erasing band at large skew angles. During the overwriting process, the footprint of a trapezoidal field bubble occupies a portion of the rectangular or parallelogram shaped bit(s) to be overwritten. When the magnetization of an unoccupied portion is in the opposite direction of the head field, the demagnetizing field from the unoccupied region shifts the trailing edge transition. When the skew angle is large, this effect can make the center transition line not parallel to the reader sensor. In this condition, one can observe a clear variation when the head reads at the two sides of the track. We call it a divergent transition, meaning the transition line diverges away from the plane of reader sensor. In this study, experimental observations prove the existence of this phenomenon. A simulation study illustrates the observation and clearly gives a complete understanding of this phenomenon. View full abstract»

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  • Modeling and Simulation of the Writing Process on Bit-Patterned Perpendicular Media

    Page(s): 3423 - 3429
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB) |  | HTML iconHTML  

    The recording physics of bit-patterned media is studied for areal densities of around 2 Tbits/inch2 . A model of the writing process, based on the head field gradient and switching field distribution, including various interference fields, is presented to extract the write-head and media parameters which are necessary to attain a wider write margin. Write head field distributions, calculated by the finite-element method, are presented for various head pole structures with side- and trailing-shields to improve head field gradient. Optimization of the pole configuration increased the gradient to over 500 Oe/nm for a head-to-soft magnetic under layer (SUL) spacing of 14 nm. Using the head field distribution, a recording performance analysis by micromagnetic simulation indicated that the write margin was improved. Position and size dispersions of the dots deteriorated the signal-to-noise ratio (SNR) and increased adjacent track erasure (ATE). View full abstract»

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  • Magnetic Recording in Patterned Media at 5–10 Tb/in ^{2}

    Page(s): 3430 - 3433
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB) |  | HTML iconHTML  

    In this paper, the feasibility of patterned media systems able to support areal densities of 5-10 Tb/in2 is examined. The systems considered used only a conventional write head, without additional electromagnetic devices. Despite the use of a shielded head and contact recording it was impossible to discriminate reliably between bits at 10 Tb/in2 . Areal densities of around 5 Tb/in2 appear feasible, but only if geometrical and material parameter dispersions are minimized. Including such dispersions reduced the maximum areal density to around 4 Tb/in2. View full abstract»

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  • Characterization of a 2 {\hbox {Tb\it/\in}}^{2} Patterned Media Recording System

    Page(s): 3434 - 3437
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (517 KB) |  | HTML iconHTML  

    The characteristics of bit patterned media with an areal density of 2 Tbit/in2 were investigated using micromagnetic simulations. The influence of dot size and position dispersions on the signal-to-noise ratio (SNR) was clarified. The head-medium synchronization tolerance (write margin) for error-free writing was calculated, and the feasibility of achieving 2 Tbit/in2 recording with bit patterned media was demonstrated. View full abstract»

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  • Simulation Study of High-Density Bit-Patterned Media With Inclined Anisotropy

    Page(s): 3438 - 3441
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (595 KB) |  | HTML iconHTML  

    A new method was proposed to realize high areal densities beyond 2 Tbit/in2 for bit-patterned media. Introduction of inclined anisotropy to the media was found to decrease the effect of magnetostatic interaction between the dots at high areal densities. Recording simulation with a perpendicular recording head revealed increased recording shift margins in both down and cross track directions. It was expected that shift margins of greater than 7 nm were expected in the both directions for recording at 2.6 Tbit/in2 using a shielded planar head for the media with inclined anisotropy. Proposed method would be one of promising techniques for realizing high density recording beyond 2 Tbit/in2. View full abstract»

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  • Writability in Discrete Track Media

    Page(s): 3442 - 3445
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    Discrete track recording has emerged as a promising candidate for high storage capacity since it reduces adjacent track erasing (ATE) and alleviates narrow head requirements. In this paper, the writability of discrete lines was studied in discrete track media (DTM) fabricated by e-beam lithography and ion-milling on perpendicular magnetic recording (PMR) media. The writability of discrete lines with finite length and three kinds of line width (50, 100, and 150 nm) is compared with continuous media on the same track. When writing current is small (less than 12 mA), the narrowest discrete lines (50 nm) are not easily magnetized, most likely due to deformed magnetic layer created by a shallow wall angle. Conversely, wider discrete lines ( ges 100 nm) are magnetized like continuous media. No difference in the level of magnetization was observed for the narrowest lines if writing current was large enough (more than 12 mA). This smooth magnetization of the narrowest line at sufficient writing current flow makes it certain that narrow discrete line can be used for high capacity storage. View full abstract»

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  • Magnetization Switching Experiments on Sub-Micron Co/Pt Multilayer Dot Using a Pulse Field Generator With Nanoseconds Duration

    Page(s): 3446 - 3449
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (378 KB) |  | HTML iconHTML  

    A pulse generator with large amplitude of 160 V and fast rise time of less than 0.4 ns has been built using a coaxial cable as a capacitor. By combining with the anomalous Hall effect technique for a single magnetic nanodot, magnetization response of one Co/Pt nanodot of 400 nm in diameter to the pulse was examined. By applying a pulse field with the maximum amplitude of 740 Oe and the duration of 10 ns, magnetization switching of the dot by the pulse was successfully observed. The pulse amplitude dependence of switching field suggested that the pulse field and the dc bias field could be treated as a simple summation of the both fields in the time scale of 10 ns. All the results of magnetization switching by the pulse field could be explained qualitatively by classical thermal relaxation process. 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.

Full Aims & Scope

Meet Our Editors

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