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Magnetics, IEEE Transactions on

Issue 2  Part 1 • Date Feb. 2006

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  • [Front cover]

    Publication Year: 2006 , Page(s): c1 - c4
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  • IEEE Transactions on Magnetics publication information

    Publication Year: 2006 , Page(s): c2
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  • Table of contents

    Publication Year: 2006 , Page(s): 89 - 90
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  • Message From the Conference Chair

    Publication Year: 2006 , Page(s): 91
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  • TMRC 2005 Conference Committee

    Publication Year: 2006 , Page(s): 92
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  • A performance study of next generation's TMR heads beyond 200 gb/in2

    Publication Year: 2006 , Page(s): 93 - 96
    Cited by:  Papers (11)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Practical level performance for ∼200 Gb/in2 has been verified by AlOx barrier tunneling magnetoresistive (TMR) heads, which resistance area product (RA) is more than 3 ohm·μm2, in perpendicular recording mode. In addition, improved AlOx barrier magnetic tunnel junctions (MTJs) formed on plated bottom shield with smoothed surface achieved TMR ratio of 25% and 16% with RA of 1.9 and 1.0 ohm·μm2, respectively, indicating over 200 Gb/in2 is also possible by the AlOx barrier TMR heads with lower RA. Furthermore, TMR heads with crystalline MgO barrier were fabricated. The MgO barrier MTJs formed on plated bottom shield with smoothed surface achieved TMR ratio of 88% with RA of 2.0 ohm·μm2, which is 3.5 times higher than that of AlOx barrier MTJs under similar RA. Dynamic electrical test was also performed for TMR heads with the MgO barrier. As a result, good readback waveform with huge output was obtained. This is the first confirmation of readback waveform generated from TMR heads with crystalline MgO barrier. Our results indicate that the future of TMR heads technology is promising beyond 200 Gb/in2 application. View full abstract»

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  • Commercial TMR heads for hard disk drives: characterization and extendibility at 300 gbit/in2

    Publication Year: 2006 , Page(s): 97 - 102
    Cited by:  Papers (33)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1352 KB) |  | HTML iconHTML  

    Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in2 in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in2 has been demonstrated. Advanced design can reach 311 Gbit/in2. View full abstract»

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  • Huge magnetoresistance and low junction resistance in magnetic tunnel junctions with crystalline MgO barrier

    Publication Year: 2006 , Page(s): 103 - 107
    Cited by:  Papers (13)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    Inserting a 4 Å-Mg metal layer between the amorphous CoFeB bottom electrode layer and the MgO barrier layer was found to be effective in realizing huge magnetoresistance effect in low-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). As a result, magnetoresistance (MR) ratio as high as 138% at resistance-area product (RA) of about 2.4 Ω·μm2 was obtained. This value is about seven times that of state-of-the-art MTJs for magnetic sensor application. X-ray diffraction analysis clarified that crystal orientation of the poly-crystalline MgO(001) barrier layer was improved by the Mg layer. It is suggested that the higher crystalline orientation of the MgO(001) barrier layer could have enhanced the coherent tunneling of Δ1 electrons, resulting in an increase of MR ratio at the low RA (thin MgO thickness) region. The annealing temperature and free layer materials have also been optimized to satisfy the requirements for practical read head application. Although this optimization resulted in a reduction in the MR ratio to about 45%-53%, this value is still more than twice the highest MR ratio of conventional MTJs. The currently developed fabrication process will accelerate the development of highly sensitive read heads for ultrahigh-density hard-disk drives. View full abstract»

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  • Simulation of noise, signal-to-noise and bandwidth of TMR and CIP/CPP GMR heads

    Publication Year: 2006 , Page(s): 108 - 113
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    In magnetic data storage the noise and signal-to-noise ratio (SNR) of the read heads is becoming more and more of a limiting factor given the smaller readout devices needed to follow the ever higher areal densities. For higher data rates this problem is aggravated by the needed wider signal bandwidths. This study presents the magnetic simulation of noise, SNR, and bandwidth for the most common types of head: tunneling magnetoresistive heads, CIP-GMR heads, and CPP-GMR heads. Such simulations allow the comparison of these different types of head. The sensitivity factors of the SNR for the most important head parameters are determined as well. The SNR of the total read path is also determined, including the head-amplifier interconnect and the electronics. View full abstract»

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  • Thermal and spin-torque noise in CPP (TMR and/or GMR) read sensors

    Publication Year: 2006 , Page(s): 114 - 119
    Cited by:  Papers (29)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    This paper considers magnetization fluctuations (mag-noise) in current-perpendicular-to-plane (CPP) read sensors, due to either thermal fluctuations or spin-torque induced instability. The former are relevant to both tunneling (TMR) and giant-magnetoresistance (GMR) devices, the latter a potentially more serious limitation most relevant to all-metal GMR sensors. Discussion of thermal mag-noise is here treated by micromagnetic simulation. Discussion of spin-torque instability includes analytical modeling combined with experimental measurements. View full abstract»

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  • Enhanced GMR ratio of dual spin valve with monolayer pinned structure

    Publication Year: 2006 , Page(s): 120 - 125
    Cited by:  Papers (2)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A new type of dual spin valve (DSV) structure with enhanced giant magnetoresistance (GMR) ratio is proposed, and the performance is characterized by the prototype read heads. The bottom part of DSV is kept as a synthetic pinned structure and only the top part adopts a monolayer pinned structure. The top monolayer pin DSV (TM-DSV) showed three percentage points higher GMR ratio and 20% higher ΔR value. After the mechanical lapping process, the monolayer pinned layer can be stabilized by not only sense current but also large stress induced anisotropy due to Villari effect. After the quantitative analysis, the induced stress is measured to be about 4.2×109 N/m2. The bias point was tuned by adjustment of Cu spacer layer thickness using the RKKY interaction between pinned layer and free layer. There is no reliability concern related to the monolayer pinned structure. In a perpendicular magnetic recording system, TM-DSV technology could successfully demonstrate the output of 35.5 mV/μm and ∼170 Gbits/in2 density feasibility. View full abstract»

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  • Relationship between head design, pole-tip magnetization, head field, and media magnetization in longitudinal recording

    Publication Year: 2006 , Page(s): 126 - 131
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1464 KB) |  | HTML iconHTML  

    We investigated the relationship between head design, pole-tip magnetization, head field, and media magnetization in longitudinal recording. At first we estimate the effective switching field of current mobile media with isotropic anisotropy, and introduce longitudinal corresponding field for the head field assessment. The smaller perpendicular component or large perpendicular field gradient of the head field at the upper pole improves the transition quality, but the small perpendicular field degrades the overwrite performance. So the ideal head field is large longitudinal and perpendicular field for good overwrite and fast attenuation with the large perpendicular field gradient for the transition quality. Some head designs make it possible to control the ratio of the perpendicular component to the longitudinal head field, by changing the pole-tip magnetization direction. As a project to control it, we discuss the effect of the bottom and upper poles configuration on the transition, overwrite, and adjacent track erasure in longitudinal recording. View full abstract»

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  • Pulse electrodeposition of 2.4 T Co37Fe63 alloys at nanoscale for magnetic recording application

    Publication Year: 2006 , Page(s): 132 - 139
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (992 KB) |  | HTML iconHTML  

    Pulse deposition of 2.4 T Co37Fe63 alloy in photoresist features with 40 nm critical dimension and high aspect ratio is presented. The design of the pulse deposition parameters is described in terms of the transport limitations through the diffusion layer, electrochemical interface stability with respect to Fe(OH)3 precipitation, and the optimum conditions for additive (Saccharin) adsorption. The alloy grain size and crystal structure in the nanoconfined electrode geometry is compared versus the thin film and relevant implications for magnetic recording are discussed. The 2.4 T Co38Fe61Pd1 alloy is introduced as a possible way to improve the corrosion properties of 2.4 T Co37Fe63 alloy. View full abstract»

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  • Ultra-high magnetic moment films for write head

    Publication Year: 2006 , Page(s): 140 - 144
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    Novel magnetic materials with ultra-high magnetic moment are presented. The Fe70Co30 alloy is known to have the highest saturation magnetization of 2.45 T in nature. On the other hand, sputtered Fe70Co30:Pd and [Fe70Co30/Pd]n super-lattice films revealed higher saturation magnetization of 2.49 and 2.57 T at room temperature, respectively, while that of a Fe70Co30 single-layered film was 2.38 T. These values seemed to be acceptable of a main pole material of the write head in the hard-disk drive with an areal recording density above 160 Gbits/in2. In addition, these films can be synthesized using a conventional sputtering apparatus as same as a Fe70Co30 films. Therefore, these films will promise a feasible way for the increase of an areal recording density without any additional technologies, such as a heat assisted recording, contact recording, or further development of the media. View full abstract»

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  • Head challenges for perpendicular recording at high areal density

    Publication Year: 2006 , Page(s): 145 - 150
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB) |  | HTML iconHTML  

    To explore recording head challenges for perpendicular recording at 200 Gb/in2 and beyond, the design, fabrication and performance of narrow track dual-element heads were studied using an ABS trailing shield writer design and a conventional CIP-GMR reader design. Parametric recording tests of these heads on low noise CoCrPt/SUL media show that, with the trailing shield design, good writability and low disk transition jitter around 2.5 nm were achieved at narrow write trackwidths down to 120 nm. In addition, peak-to-peak signal amplitudes around 1 mV and T50 widths around 28 nm were also achieved at read trackwidths around 60 nm. The areal density potential of these heads was studied using a PRML channel at ∼50 MB/s data rate. Results show linear densities around 1000 Kbpi at ontrack byte error rates of 10-4, and track densities around 200-240 ktpi using a criterion of 15% offtrack to trackpitch ratio. In all, areal densities of 210-230 Gb/in2 were achieved with these head and disk components. View full abstract»

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  • Direct and reverse overwrite processes in perpendicular recording

    Publication Year: 2006 , Page(s): 151 - 156
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Excellent overwrite (OVW) performance has to be guaranteed for two cases, namely, the case where a low frequency (LF) background data pattern is overwritten by a high frequency (HF) data pattern and the reverse case, e.g., the reverse overwrite (ROVW) situation where a high linear density background pattern is overwritten by a low linear density data pattern. In this work, the spectra of both OVW and ROVW processes have been investigated experimentally to identify the intrinsic characteristics of residual noise in the OVW and ROVW processes in perpendicular recording. Specifically the spectra of both OVW and ROVW processes have been quantitatively analyzed to quantify the characteristics of relevant amplitude modulation or amplitude cancellation process. View full abstract»

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  • Media saturation and overwrite in perpendicular recording

    Publication Year: 2006 , Page(s): 157 - 162
    Cited by:  Papers (17)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB) |  | HTML iconHTML  

    A novel spin-stand method for measuring the perpendicular write pole "footprint" is proposed. This method allows the detailed study of the spatio-temporal pole footprint dynamics and the two-dimensional media saturation and noise. Experimental footprint measurements are presented and the problems caused by the magnetic nonuniformity of the poles are addressed. The perpendicular overwrite process is studied by time-domain waveform analysis. The spatial distribution of the overwrite signal is determined by the geometry and the magnetic uniformity of the write pole footprint. The dependence of recording parameters on write current overshoot in perpendicular recording is also analyzed. View full abstract»

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  • Write field measurements of a perpendicular head on a soft underlayer film

    Publication Year: 2006 , Page(s): 163 - 165
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    We demonstrate a technique to measure the field of a perpendicular head on a soft underlayer. We built a current-perpendicular-to-the-plane giant magnetoresistive sensor deposited on a soft underlayer and placed it on the write-read contact tester. Scanning a perpendicular head over the device with sub-nm resolution allowed us to map the field spatially and by changing the writer current, obtain saturation curves of both the main pole and the return pole. View full abstract»

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  • Direct measurement of magnetodynamics in a perpendicular recording system

    Publication Year: 2006 , Page(s): 166 - 170
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    To characterize the magnetodynamic properties of a perpendicular recording system, consisting of a pole head, a recording layer, an exchangebreak layer, and a soft underlayer (SUL), we have built a test vehicle by depositing either the SUL, or the full medium stack on the air-bearing surface of the recording head. Using ultra-high-speed scanning Kerr microscopy, the intrinsic switching characteristics of the SUL and the impact of the recording layer on the former has been measured. One important feature found is the formation of vortices during reversal which are much larger than the pole area as well as evidence for spin wave excitation in the SUL. Both fast write current steps, and complex write current waveforms have been applied and significant differences of the magnetic responses are observed. Though the Kerr signal probes the temporal evolution of the SUL surface magnetization, it is possible to determine the onset of the recording layer switching by taking its magnetostatic coupling to the SUL into account. The magnetization state of the recording layer also impacts the switching speed of the SUL. The noise characteristics of the Kerr signal gives information about nonreproducible magnetization processes in the SUL. View full abstract»

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  • Perpendicular drive integration

    Publication Year: 2006 , Page(s): 171 - 175
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    This paper reports on progress in perpendicular drive integration. In the first part, the performance of a series of perpendicular media with different coercivity (5-6 kOe), nucleation field, and soft-underlayer thickness (120/80 nm) is compared using two different head designs. Good overwrite and bit error rate performance is achieved for all head/media combinations. Higher coercivity leads to lower linear density but higher track density, resulting in approximately equal areal density capability. The thinner soft underlayer causes wider erase bands and therefore a loss of areal density. Wide-area track erasure measurements were performed on all media. The media with lower coercivity do not show any measurable amplitude loss, due to their larger absolute value of the nucleation field and the smaller write current needed to write on them. Two types of single-head, 7200 RPM desktop perpendicular drives (40 and 80 GB capacity) were built using 95 mm perpendicular media. They both achieve good bit error rate and off-track capability in all zones. The thermal decay for the 40 GB drive was measured and compared to a similar longitudinal drive. It was found that the thermal decay rate is much smaller in the case of the perpendicular drive in the range -6°C to +80°C. View full abstract»

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  • Channel characterization methods using dipulse extraction

    Publication Year: 2006 , Page(s): 176 - 181
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    We present dibit extraction with a nonlinear representation of the readback signal in terms of a finite Volterra series. We show that the extracted dibit response is the linear combination of the cyclically shifted Volterra kernels. Then we explore several implications of this to dibit extraction and system characterization such as the indistinguishability of physical mechanisms from output observation, bandwidth expansion, and requirements on the length of the pseudorandom binary sequences that arise when viewing the system in the wider context of the finite Volterra series. View full abstract»

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  • Recording over 15 ktpi using multichannel heads in a tape system

    Publication Year: 2006 , Page(s): 182 - 187
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB) |  | HTML iconHTML  

    In magnetic recording systems, it has been reported that sufficient signal-to-noise ratio (SNR) was obtained with a narrow track width, using a spin-valve head and metal-evaporated tape. In order to apply this to a helical-scan tape system, techniques for writing narrow tracks and reading them exactly were required. However, the degree of mechanical accuracy demanded was too high to realize. With this in mind, we have developed multichannel heads which can write and read certain tracks with a single scan, as well as a nontracking technique removing the need for such precise mechanical accuracy. A prototype tape drive employing these techniques was developed, and a track density exceeding 15 ktpi was achieved. View full abstract»

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  • Drive-independent data recovery: the current state-of-the-art

    Publication Year: 2006 , Page(s): 188 - 193
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    The term "data recovery" herein refers to accessing logically and/or physically damaged storage media, for which no functioning backup exists. The state-of-the-art physical techniques for recovering data from failed hardware can all be described as "part replacement." To achieve high data density and high manufacturing yields, modern drives are "hyper-tuned" in the factory so that their data layout, zone frequencies, and various channel settings are optimized for each head, surface, and zone. This greatly complicates part replacement because a transplanted headstack, for example, no longer matches the servo, preamp, and read channel parameters that were optimized for the original headstack. Methods and challenges are discussed for replacing, or "refreshing," firmware and system area information and for replacing all of the drive's electronics. The data recovery industry's point of view, limitations of current techniques, and some probable future directions in data recovery are also presented. It is predicted that data recovery will be more important in the future as drives are exposed to more extreme mobile environments. Drive manufacturers may be able to differentiate themselves from their competition by designing for recoverability. View full abstract»

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  • Extraction of timing error parameters from readback waveforms

    Publication Year: 2006 , Page(s): 194 - 199
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    In this paper, we consider the problem of modeling the timing error process in magnetic recording systems. We propose a discrete-valued Markov model for the timing error process, and design two methods (data-aided and nondata-aided), based on the Baum-Welch algorithm, to extract the model parameters from the readback waveforms. The channel model we consider is an intersymbol interference (ISI) channel with additive Gaussian noise. The continuous-time readback signal at the output of the channel is sampled at baud-rate. Simulation results show that the estimated parameters are close to the actual values and the convergence is attained in a few iterations of the Baum-Welch algorithm. We also demonstrate the usefulness of the accurate model extraction by comparing a fine-tuned Markov timing recovery loop to the standard Mueller and Muller detector with a tuned second-order loop filter. View full abstract»

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  • System perspectives for the application of structured LDPC codes to data storage devices

    Publication Year: 2006 , Page(s): 200 - 207
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    We have three main goals in this paper. First, we will show the equivalences and relationships among some of the well-known classes of structured low density parity check (LDPC) codes. Second, we consider application of these codes to magnetic recording channel. We will make performance comparisons not only with bit-error-rate (BER) metric but also with sector failure rate (SFR) as the comparison dimension. Such a comparison is more meaningful from a system analysis perspective. Finally, we consider the case of these structured LDPC codes concatenated with conventional Reed-Solomon (RS) codes. We believe LDPC codes will not completely replace RS codes in the future storage devices. From this perspective, for LDPC codes to be contenders for future architectures, they will need to work in harmony with the outer RS codes. This implies that we have to take into account the redundancy introduced by the overall coding scheme, that is, RS code in concatenation with LDPC code, to reach meaningful comparisons from a system design perspective. 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