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Magnetics, IEEE Transactions on

Issue 1 • Date Jan. 2008

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Displaying Results 1 - 25 of 34
  • [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): 85 - 86
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  • Message from the Conference Chair

    Page(s): 87
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  • Klaas Berend Klaassen September 10, 1941 - September 3, 2007

    Page(s): 88 - 89
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  • All-Metal Current-Perpendicular-to-Plane Giant Magnetoresistance Sensors for Narrow-Track Magnetic Recording

    Page(s): 90 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (359 KB) |  | HTML iconHTML  

    Read heads using current-perpendicular-to-plane (CPP) giant magnetoresistance sensors have been fabricated and tested under high-density recording conditions. A magnetoresistance of 5.5% and shield-to-shield spacing of 45 nm have been achieved by using an all-metal single-spin-valve with Heusler-alloy-based free and reference magnetic layers. Read heads with magnetic read widths ~45 nm were tested on perpendicular media, resulting in signals above 1 mV and signal-to-noise ratio ~30 dB. Linear densities in excess of 1050 kbpi were achieved with thermal fly-height control, compatible with recording areal densities of ~400 Gb/in2. Current-induced spin-torque effects in the recording head were observed to result in rapid performance degradation above a threshold bias voltage of about 75 mV, corresponding to current densities >108 A/cm2. View full abstract»

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  • CPP–GMR Heads With a Current Screen Layer for 300 \hbox {Gb/in}^{2} Recording

    Page(s): 95 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) heads with a current screen layer were fabricated, and the recording performance was measured. An output voltage of 1.9 mV and head-amp signal-to-noise ratio (SNR) of about 30 dB were obtained from a 50-nm-wide head with an operating voltage of 120 mV. The MR ratio was 4%-5%, shield gap was 36 nm and resistance was 72 Omega. With using the thermal fly-height control (TFC), the fabricated head showed a potential to yield a 382 Gb/in2 recording (1252 kBPI times 305 kTPI). The current screen structure reduced the spin torque noise since just a low sensing current of 1-2 mA was required for obtaining a high output. Newly developed CPP-GMR films with a current screen layer showed the MR ratio of 18%-19% with the RA product of 0.2-0.3 Omega ldr mum2. Calculation showed that this film allows us to achieve 30 dB or more in the head-amp SNR when the sensor width was 40 nm or larger. The current screen CPP-GMR head is thus an attractive candidate that has a high potential suitable for an areal density of 500 Gb/in2 or more. Below 40 nm, an all metal CPP-GMR head with the MR ratio of 10% or more would be the best candidate. View full abstract»

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  • Accelerated Lifetime Test for TMR Heads by Ramped Stress

    Page(s): 100 - 103
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    Ramped stress breakdown test was applied to estimate lifetime of tunneling magnetoresistance (TMR) heads for the intrinsic and extrinsic breakdown failure mode based on both E and 1/E models. The ramp voltage stress failure was transferred into the constant voltage stress prediction and closed form expressions of time-to-failure for both E and 1/E models were deduced. The parameters for these expressions were fitted by the experimental data at various ramp step times and the time-to-failure was calculated using these fitted parameters. The heads with larger breakdown voltage showed longer lifetime for the same ramp step time, and the shorter lifetime heads were from the lower magnetic reader resistance range. The thermal acceleration was too slow for TMR lifetime projection, and the lifetime showed bimodal distribution due to the extrinsic and intrinsic breakdown behaviors, the extrinsic breakdown heads showed shorter lifetime compared with the intrinsic breakdown heads. View full abstract»

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  • Anti-Static Robustness Enhancement and High-Frequency Noise Pickup Immunity by Internal Shunting for Tunneling Magnetoresistive Sensors

    Page(s): 104 - 106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (623 KB) |  | HTML iconHTML  

    Internal shunting is introduced on tunneling magnetoresistive heads to enhance device anti-static robustness and external high-frequency noise pickup immunity. The details of the shunting scheme and the mechanism leading to both anti-static robustness and reduced high-frequency noise pickup are discussed. View full abstract»

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  • A Study of Media Dependence of Trailing Shield Perpendicular Write Head

    Page(s): 107 - 112
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1474 KB) |  | HTML iconHTML  

    The performance of two types of trailing shield perpendicular writers with either double coil or single coil are investigated. It has been found that signal-to-noise ratio (SNR) performance of different designs strongly depends on the tradeoff of field gradient and writability. Reverse DC noise analysis is used to understand the recording properties of head and media quantitatively. To realize the performance advantages of the single coil design and to suppress the trailing shield erasure, a novel single coil structure with double write gap is proposed. View full abstract»

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  • High Magnetic Saturation Poles for Advanced Perpendicular Writers

    Page(s): 113 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB) |  | HTML iconHTML  

    Advanced perpendicular writers continue to demand maximum write fields, fast rise times at ever vanishing head-media spacing and strict reliability standards. This means that the asymptotic progression to a 2.4 T pole with nearly ideal magnetic response continues. At the same time we must control critical pole dimensions, fabricate at a reasonable cost while protecting against corrosion and erasure risks. We will review progress made to meet this challenge in a discussion of high moment materials utilizing electroplating and sputter deposition for single layer films and laminates. Concerns for corrosion will be assessed and minimized by controls on key contaminants. Micromagnetic modeling will be used to study the phenomenology and expected performance impacts of these various materials and structures. Results will be used to provide a better insight into the potential materials/design tradeoffs that must be made. In conclusion, performance and reliability will be assessed through electrical testing. View full abstract»

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  • Integrated Heat Assisted Magnetic Recording Head: Design and Recording Demonstration

    Page(s): 119 - 124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (877 KB) |  | HTML iconHTML  

    Scaling the areal density, while maintaining a proper balance between media signal-to-noise ratio, thermal stability, and writability, will soon require an alternative recording technology. Heat assisted magnetic recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g., by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) magnetic field delivery; 2) optical delivery; and 3) magnetic and optical field delivery integration. Thousands of these HAMR heads were built into sliders and head-gimbal assemblies, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~ lambda/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. A magnetic force microscopy image of HAMR media shows that non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, but transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is ~350 nm, but the written track is ~200 nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned. View full abstract»

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  • Microwave Assisted Magnetic Recording

    Page(s): 125 - 131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1627 KB) |  | HTML iconHTML  

    In this paper, we present a novel mechanism for recording at a head held significantly below the medium coercivity in a perpendicular recording geometry. By applying a localized ac field at adequate frequency to the perpendicular recording medium, saturation recording can be achieved with recording field amplitudes significantly below the medium coercivity, or the medium perpendicular anisotropy field. A scheme utilizing spin torque to generate a localized ac field at high frequency (tens of gigahertz) with kilo-oersted field amplitude in the medium is proposed along with a systematic modeling analysis. Recording simulations at high linear densities are presented. View full abstract»

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  • Production and Performance of {\hbox {Si/SiO}}_{2} Magnetic Recording Head Sliders

    Page(s): 132 - 137
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    An alternative has been sought for the very hard ceramic material (Al2O3 plus TiC) used as the substrate for magnetic recording heads. We have substituted silicon as the substrate and slider body material; the primary insulator enclosing the recording head was made of SiO2. We built and tested these sliders with full read and write capability in disk drives. Si provides improvement with respect to hardness, modulus, and thermal conductivity, and adds the potential of active electronics located immediately adjacent to the recording head. We describe a novel means of producing heads, using entirely dry etching, rather than diamond sawing. The sliders were etched from the finished wafers in the form of individual sliders, rather than rows of sliders, and were processed individually through to completion. Conventional air bearings were etched into the sliders, suspensions were attached, and drives were built and tested. The outcome shows a profound advantage in the mechanical head/disk interaction, particularly under shock conditions. Other results and slider characterization are described. View full abstract»

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  • Optimal Slider-Disk Surface Topography for Head-Disk Interface Stability in Hard Disk Drives

    Page(s): 138 - 144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1399 KB) |  | HTML iconHTML  

    In order to achieve an areal density of 1 Tb/in2 and beyond, not only the mechanical spacing between the slider and the disk but also the track misregistration (TMR) and the fly height modulation (FHM) should be reduced below current levels. But at reduced mechanical spacing there will be elevated excitation due to slider-disk contacts resulting in increased slider vibrations and head-disk interface (HDI) failures. Thus, there is a need to study the effect of slider-disk topography on the slider dynamics and stability at a higher level of complexity. In this paper, we do so by dividing the slider-disk surface features into three regimes based on the amplitude and the wavelength range of the features. Further, we have also proposed several ways of achieving an optimal slider-disk topography that can help reduce the slider vibrations and increase the stability of the HDI. View full abstract»

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  • Low Flying-Height Slider With High Thermal Actuation Efficiency and Small Flying-Height Modulation Caused by Disk Waviness

    Page(s): 145 - 150
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (955 KB) |  | HTML iconHTML  

    To sustain an ultra-low and stable flying height (FH) is crucial for achieving high areal densities in magnetic recording. Recently, a new method called thermal flying height control (TFC) has been introduced to the latest generations of disk drives for precise control of slider-disk spacing. It is noted that the TFC technique is able to eliminate almost all static FH loss, but is unable to circumvent dynamic FH loss such as flying height modulation (FHM) due to disk waviness. It is therefore advantageous to have both high thermal actuation efficiency and low FHM due to disk waviness characteristics in a TFC slider design. This paper investigates the effects of air bearings on the thermal actuation efficiency and the capability in following disk waviness of the TFC sliders. Air bearing surface (ABS) design strategies for TFC slider are proposed and investigated with simulations. The results show that both excellent thermal actuation efficiency and strong capability in following disk waviness can be achieved through proper arrangements of air bearing pressure distribution on the ABS of TFC sliders. View full abstract»

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  • Head Slider Designs Considering Dynamic L/UL Systems for 1-in Disk Drives

    Page(s): 151 - 156
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    This paper focuses on air bearing surface (ABS) design optimizations in order to reduce the lift-off force during the unloading process while satisfying the desired static flying performances. Since it takes a huge amount of computational time to solve time-dependent dynamic load/unload (L/UL) equations, an approximate lift-off force is created as a function of the air bearing suction force and flying attitude parameters by the kriging method. The design framework is employed in wrapping effectively and connecting the kriging model and the static analyzer to the optimizer. An optimization problem is formulated to minimize the amplitude of the lift-off force during the unloading process while keeping the flying height, pitch, and roll angles within suitable ranges over the entire recording band as well as reducing the possibility of slider-disk contact in steady state. Then, two different sizes of slider models are optimally designed for L/UL applications with 1-in disk drive. The L/UL simulation results show that the optimized ABS designs have reduced the lift-off force in the loading process by approximately 62% and 11% for pico and femto design respectively, while satisfying desired static flying performance. In addition, results demonstrated that the optimum slider incorporated with the suspension were not only properly unloaded onto the ramp but also smoothly loaded onto the rotating disk. Therefore, it is believed that the proposed design approach works efficiently in ABS designs for L/UL applications. View full abstract»

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  • Friction Force Measurements and Modeling in Hard Disk Drives

    Page(s): 157 - 162
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (582 KB) |  | HTML iconHTML  

    Friction in a head disk interface (HDI) is investigated considering the surface energy of the lubricant and the type of carbon overcoat (COC). Perfluoropolyether Z-Tetraol lubricant with A20H additive is applied on two types of COC (type-A and type-B) with lubricant thicknesses in the range of 11-19 A. The polar and dispersive components of the surface energy are measured from contact angle experiments. For each case, friction is measured using actual hard disk drives, and they are compared with the measured surface energy values of the disk samples. As the lubricant thickness increases, both the surface energy and friction decrease. Comparing friction and surface energy values for the two types of COC disks, type-A disks are found to exhibit lower surface energy and higher friction at all lubricant thicknesses. This is attributed to the effects of surface roughness, surface energy of the COC film, and lubricant interactions. View full abstract»

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  • Feasibility of Recording 1 \hbox {Tb/in}^{2} Areal Density

    Page(s): 163 - 168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    Exchange coupled composite media has a lower switching field compared to conventional perpendicular media at the same level of thermal stability, making it promising for high areal density recording. In this paper, we propose head and media specifications, calculated micromagnetically at a density of 1 Tb/in2, using a composite media with a synthetic antiferromagnet hard layer. We assume realistic constraints such as jitter to bit length ratio, skew, seed layer, and grain boundaries. T50 of the read back pulse is estimated using a current perpendicular to plane (CPP) giant magnetoresistive (GMR) reader and the magnetization noise is calculated. The signal to dc noise ratio is also estimated for the media used. View full abstract»

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  • Exploring Low Loss Suspension Interconnects for High Data Rates in Hard Disk Drives

    Page(s): 169 - 174
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1094 KB) |  | HTML iconHTML  

    For high data rate applications, current suspension interconnect solutions should stay above 50 Ohm differential impedance (Zdiff ) due to footprint limitations and frequency dependent ohmic losses of the stainless steel plane at low Zdiff . This paper describes the impedance and bandwidth (BW) design space of today's interconnects and also shows why this technology is still compatible with current system front-ends up to 3 Gb/s. Furthermore, the benefits of reduced power and higher overshoot using less than 50 Ohm impedance and high bandwidth interconnects are explored with a system model. Three alternate low impedance interconnect structures are used to demonstrate these benefits, and are explored analytically and evaluated for mechanical tradeoffs. View full abstract»

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  • Advanced Interconnect Design for High Data Rate Perpendicular Magnetic Recording

    Page(s): 175 - 180
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (924 KB) |  | HTML iconHTML  

    For present write channel current waveforms, a bandwidth efficiency of 1/2 bps/Hz is shown to be achievable which is 1/4 that of the read channel bandwidth efficiency. Further, with an improved write channel current waveform, the writer bandwidth requirement can be reduced by 1/2 to enable a bandwidth efficiency of 1 bps/Hz. View full abstract»

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  • Iterative Decoding Based on Error Pattern Correction

    Page(s): 181 - 186
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    The error-pattern correction code is a code specialized to correct dominant error patterns observed at the channel detector output in heavy intersymbol interference channels. In this paper, we consider a turbo-equalizer system that utilizes the error-pattern correcting code (EPCC) as a building component. A soft-input soft-output (SISO) decoder for the EPCC is described, and the performance of the proposed turbo equalizer is compared with those of the conventional turbo equalizer and a low density parity check (LDPC) code system. View full abstract»

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  • Macroscopic and Microscopic Approaches in Sector Failure Rate Estimation

    Page(s): 187 - 192
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (225 KB) |  | HTML iconHTML  

    The sector failure rate (SFR) is extremely small at normal operating conditions of hard disk drives. In practice, it cannot be obtained by counting as that would require prohibitively large simulation times. Therefore, appropriate statistical models characterizing the distribution of error symbols are used in order to estimate the SFR. In this paper, we look at the underlying philosophy of existing estimation methods and classify them into macroscopic and microscopic types. We observe that the microscopic approach is well suited for certain iterative channels. View full abstract»

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  • A New Read Channel Model for Patterned Media Storage

    Page(s): 193 - 197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (652 KB) |  | HTML iconHTML  

    It is conceivable that early generations of patterned media will utilize read heads whose dimensions are several times larger than an "island" of magnetization. For such a scenario, we propose a "multiple islands per read head" model where the output from the read head is a function of the magnetization from several independently written tracks of islands. In particular, we focus on a "3 islands per read head" model where the output from the read head is a function of the magnetization from three independently written tracks of islands. The readback signal is determined from a finite track-width magnetoresistive (MR) head model using reciprocity calculations, and two noise sources - island position jitter and AWGN electronics noise - are considered. By sampling the noisy signal at intervals corresponding to the down-track island separation, we obtain a discrete-time readback channel model whose performance is obtained under maximum-likelihood sequence detection. View full abstract»

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  • Viterbi Detector for Non-Markov Recording Channels

    Page(s): 198 - 206
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (265 KB) |  | HTML iconHTML  

    Channel noise in modern perpendicular channels is well approximated by a linear jitter model. In this paper, we propose a new type of Viterbi detector matched to such a channel model. The differentiating feature of this detector is recursive evaluation of whitened noise strengths for survivor paths using the on-the-fly Cholesky factorization of path-dependent correlation matrices. We study the performance of the detector using the simplest example of low-density channels with intersymbol interference length equal to three. We find that at BER = 10-4, the new detector outperforms the data-dependent AR-detector of the comparable complexity by about 0.9 dB. 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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Meet Our Editors

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