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Magnetics, IEEE Transactions on

Issue 2 • Date Jan. 2007

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Displaying Results 1 - 25 of 95
  • [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): 589 - 591
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  • Message from the Conference Chair

    Page(s): 592
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  • TMRC 2006 Conference Committee

    Page(s): 593
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  • Relationship Between Head Design and Media Remanent Magnetization in Perpendicular Magnetic Recording

    Page(s): 594 - 599
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3027 KB) |  | HTML iconHTML  

    This paper presents micromagnetic modeling results in a perpendicular magnetic recording, which consists of a single-pole head and double-layered media. To know the inplane head field contribution, the relationship between applied angular field and media remanence is studied, and we propose a perpendicular corresponding field for the head field assessment, which can explain media remanence as well such as the main-pole footprint on the media. The shielded-pole/single-coil head shows the best signal-to-noise ratio but the overwrite performance is somewhat poorer than monopole heads, with a large positive to negative head field, which implies a large field gradient. Although the shielded-pole head has smaller erase bands with straight transitions, it can cause trailing-shield-related erasure by the negative field under the high write current input in the single-coil design View full abstract»

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  • Return Field-Induced Partial Erasure in Perpendicular Recording Using Trailing-Edge Shielded Writers

    Page(s): 600 - 604
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    Return field-induced partial erasure (RFPE) in trailing-edge shielded perpendicular writers has been studied, both by modeling and by experiments. For a given head-media combination, the return field underneath the trailing shield increases with increasing write current. Once exceeding a certain threshold, it will cause partial erasure of the bits that have just been written by the main pole. Recording performance, such as reverse overwrite, spectral signal-to-noise ratio, and bit-error rate are all found degraded at high write currents, due to RFPE. Design optimization of both head and media together is needed, in order to maximize the advantage of a trailing-edge shielded pole head and minimize the impact of RFPE View full abstract»

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  • Challenges for Perpendicular Write Heads at High Recording Density

    Page(s): 605 - 608
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    Perpendicular recording technology has become the main stream for 130 Gb/in2 HDD products. In this paper, challenges in perpendicular write head are discussed. Design tradeoffs and concerns of narrow-track single-pole heads, trailing shield heads, floating TS heads, and wrapped-around-shield (WAS) heads are discussed. Experimental data show that WAS heads provide good narrow track and high linear density performance. An areal density of 343 Gb/in2 has been achieved at a very aggressive magnetic spacing condition View full abstract»

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  • High Moment Materials and Fabrication Processes for Shielded Perpendicular Write Head Beyond 200 Gb/in2

    Page(s): 609 - 614
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    Commercial hard-drive products utilizing perpendicular magnetic recording technology have recently been announced and introduced. In this paper, we review key magnetic materials characteristics and wafer process attributes in fabricating perpendicular write heads. It becomes increasingly important for write-head materials to possess not only high magnetic moment, but also optimal coercivity, remanence, anisotropy Hk, magnetostriction, and stress in order to meet head performance and reliability requirements. Advanced materials and film architectures discussed in this paper resulted in a significantly improved performance margin, including reduced pole erasure; hence enabling higher recording densities. Novel wafer-processing techniques are required for fabrication of 3-D pole features with controlled shape, and with critical dimensions of less than 150 nm. The advance in wafer process has been driven by rapidly decreasing trackwidth, as well as by the evolving head architecture from unshielded rectangular pole to shielded trapezoidal pole View full abstract»

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  • Effect of Oxygen Incorporation on Microstructure and Media Performance in CoCrPt–SiO2 Perpendicular Recording Media

    Page(s): 615 - 620
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    The effect of oxygen incorporation on microstructure and media performance in CoCrPt-SiO2 films with various oxygen contents (OC) from 3 to 10 at% at different CoCrPt-SiO2 film thicknesses (tMAG) from 2 to 27 nm is investigated. Nonuniform microstructure with less grain isolation close to Ru and more grain isolation at the top region is clearly seen. Higher density of stacking faults is found at the top region. A higher OC is needed to reduce the thickness of the initial layer with less grain isolation. The increase in coercivity and saturation magnetization with increasing OC is due to the formation of lower Cr and higher Pt-containing core grains caused by the preferred oxidation of Cr. These excess Pt atoms mostly align along the c-axis direction. The magnetocrystalline anisotropy constant enhanced by the excess Pt improves thermal stability factor but it is sensitive to temperature. Crystallographic c-axis orientation and magnetic anisotropy dispersion deteriorate with increasing OC but are independent of tMAG View full abstract»

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  • Magnetic Anisotropy of Perpendicular Media: Measurement and Intermediate Layer Effect

    Page(s): 621 - 626
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (414 KB) |  | HTML iconHTML  

    We investigated the uniaxial magnetic anisotropy of perpendicular magnetic film formed on various intermediate layers (IMLs) using torque magnetometry. We carefully analyzed the shapes of the torque curves so that we could separate the magnitudes of the quadratic (Ku1) and quartic (Ku2) anisotropy energy terms. However, it turned out that the Ku values contained inevitable errors caused by the dispersion of magnetic anisotropy when they were estimated at a finite measurement magnetic field (Hext), and that the true Ku2 terms were close to zero among all of our samples. Then, we utilized the Hext dependence of the apparent Ku values for the analysis of magnetic anisotropy dispersion of perpendicular media. Through a systematic study on various IMLs, it was directly proven that the magnetic dispersion of the CoCrPt-SiO2 storage layer arose not only from the addition of oxide into the storage layer but also from the crystal growth on ill-suited IMLs. We further demonstrated that a Pt-Cr/Ru-laminated IML successfully avoided magnetic dispersion, which led to excellent recording performance with less total spacing between the storage layer and the soft-magnetic underlayer View full abstract»

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  • Determination of the Anisotropy Field Distribution in Perpendicular Media and Its Correlation With Microstructure and Recording

    Page(s): 627 - 632
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    A complex transverse ac susceptibility (chiT) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin-film recording media. The technique has been used to measure the dispersions in grain size and the anisotropy field of perpendicular magnetic recording media. Experiments have been designed to study the key factors contributing to the anisotropy field distribution (sigmaHk) in perpendicular media. The correlation between anisotropy dispersion, stacking faults, and recording performance have also been studied. A good correlation between stacking faults and sigmaHK has been established. Lower stacking faults result in smaller anisotropy distribution and better media signal-to-noise ratio. The main factors controlling stacking faults are studied. Theoretical studies of the effect of interactions on the chiT are also presented View full abstract»

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  • Magnetic and Microstructural Properties of CoCrPt:Oxide Perpendicular Recording Media With Novel Intermediate Layers

    Page(s): 633 - 638
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    Novel recording media layer structures for reducing the spacing between the soft magnetic underlayer and the writing head have been studied. In this paper, the kink in Kerr loops at zero fields is explained to arise from the depth-sensitive Kerr effect. Novel intermediate layer structures with two (RuCu) or three elements (RuCr:Oxide) are also proposed to reduce the grain size in the intermediate layer. This would, in turn, lead to a reduced grain size and grain size distribution in the CoCrPt:SiO2 recording layer View full abstract»

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  • Microstructure and Exchange Coupling of Segregated Oxide Perpendicular Recording Media

    Page(s): 639 - 644
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    The magnetic properties and corresponding microstructure of (Co 80Pt20)x (metal oxide)1-x perpendicular recording media have been studied as a function of the volume percentage (vol%) of metal oxide sputtering into the magnetic film. The exchange coupling field (Hex) estimated from the coercivity (H c) and nucleation field (Hn) decreases rapidly between 0-20 vol% of metal oxide. The analytical transmission electron microscope composition analysis of (Co80Pt20)x(TiO2)1-x media confirms that the microstructure includes crystalline grain cores in an apparently amorphous oxide matrix. The grain cores comprise only Co and Pt in a nearly constant ratio independent of the vol% of oxide addition. The amorphous matrix contains Co, Ti, and O, but no Pt. The Co concentration is nearly constant in grain boundary and core regions, unlike high-temperature longitudinal recording media wherein Co segregates to form a concentration gradient in the grain core. Perpendicular media thus maintain fairly high anisotropy of the grain core phase, even for very high-oxide concentrations that significantly decrease remanant magnetization (Mrt), Hc, and thermal stability (KuV/kT) View full abstract»

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  • Current-in-Plane GMR Trilayer Head Design for Hard-Disk Drives: Characterization and Extendibility

    Page(s): 645 - 650
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    The current-in-plane giant magnetoresistive (GMR) trilayer readback sensor (CIP-3L), where only one permanent magnet at the back edge of the GMR stack is used to stabilize and bias a dual free layer system, is reviewed. Micromagnetic modeling is employed to show that the design has improved efficiency over abutted junction (ABJ) tunneling magnetoresistive (TMR) head designs. An experimental evaluation of how permanent magnet thickness (PM Th), interlayer exchange coupling (J), and stripe height impact the signal-to-noise ratio, symmetry, and stability of prototype CIP-3L heads is conducted. The study indicates that PM Th >400 nm, J<-0.8 erg/cm2, and a read width to SH aspect ratio of 1:1 to 0.75:1, gives optimal transfer curve performance. A head gimbal assembly spinstand comparison on perpendicular recording media with best-in-class TMR readers shows that although the amplitude of the CIP-3L heads is lower (believed to be process related), the symmetry, stability, and most important, bit-error rate normalized to electrical write width and read width, are comparable. In addition, the CIP-3L design shows better linearity and low-frequency noise performance than TMR heads. The areal density performance of the best CIP-3L heads shows 195 Gb/in2 recording capability and linear densities of 1100 kbpi View full abstract»

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  • Current-in-Plane Giant Magnetoresistance Sensor Using a Thin Cu Spacer and Dual Nano-Oxide Layers With a DR Greater Than 20 Ohms/sq.

    Page(s): 651 - 656
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    The magnetoresistance (MR) of the current-in-plane spin-valve, which is currently utilized as the readback sensor in the majority of hard disk drives, has reached a maximum MR of DR/Rmin.~20% and DRsheet~4 Omega/sq. A new sensor film stack will be introduced here that utilizes a trilayer (CoFeCuCoFe) where the Cu interlayer is very thin (~10 Aring) to enhance the MR and where the Cu thickness is chosen such that the ferromagnetic Neel coupling and the antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between the CoFe layers partially cancel one another, to maximize the sensitivity. By changing the Cu interlayer thickness, the overall interlayer coupling was adjusted from about -0.05 erg/cm2 to -0.4 erg/cm2 while keeping the MR large. Nano-oxide layers (NOLs) are also incorporated below and above the trilayer sensor to enhance the MR. An example of this sensor is NiFeCr 20 Aring/CoFeO 10 Aring/CoFe 15 Aring/Cu 10.5 Aring/CoFe 15 Aring/AlO 30 Aring and will be referred to as CIP-3L. With the combination of the thin Cu spacer, the NOLs and minimal additional layers to shunt the current around the trilayer sensor (no antiferromagnetic material and no pinned layers), as deposited sheet films with an MR of DR/R >25% and DR/sq. >20 Omega/sq. were achieved. This paper shows the optimization of the sensor stack, such as film thicknesses, NOL material, and oxidation process, the adjustability of the interlayer exchange coupling between the CoFe layers and also shows the repeatability of the sensor deposition View full abstract»

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  • Scalable Toggle Read Sensor

    Page(s): 657 - 662
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    A read sensor working in the toggle mode is presented. The free layer comprises a balanced synthetic-antiferromagnetic (SAF) multilayer. The magnetization of the free SAF layer is perpendicular to the air-bearing surface (ABS) when bias field is applied in the direction of the ABS. The magnetization of the reference layer is fixed to be parallel to the ABS instead of perpendicular as is the conventional case. The sensitivity of the toggle read sensor (for small track width) improves significantly compared to the conventional abutted junction bias type. For a toggle sensor with long height structure, performance in both the sensitivity and linearity has also been improved because increased sensor height can be used for the lower bias field. The lower bias field is also compatible with the small gap structure of an in-stack bias scheme. Simulation results also show that the thermal magnetic noise in the toggle sensor is much smaller than that in the conventional biased sensor. Experimental results for both the current-in-plane (CIP) and tunneling-magneto-resistive (TMR) sensors with toggle mode are consistent with our calculation results View full abstract»

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  • Electrical Low-Frequency Noise in Tunneling Magnetoresitive Heads: Phenomena and Origins

    Page(s): 663 - 670
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    Tunneling magnetoresistive (TMR) heads have been observed to exhibit relatively large low-frequency noise. Observation in a saturating field reveals that a substantial part of this noise is of electrical origin. Two distinctly different electrical noise phenomena are observed: 1/f noise and random telegraph (RT) noise. 1/f noise appears in all heads, RT noise only in some. The magnitude of the noise tracks the device resistance and the electrical bias. Therefore, the question arises if it is caused by resistance fluctuations or by the electrical bias. To answer this question, the paper describes a measurement setup to determine the TMR device noise in thermodynamic equilibrium (no bias). It is concluded that at zero bias there is no electrical low-frequency noise; neither 1/f noise nor RT noise was detected. Further, the paper proposes an electroacoustic model for the origin of the 1/f noise and estimates the expected magnitude. For the RT noise, in addition to the well-known trapped charge blocking model, an electromigratory model is proposed to better cover all observed RT noise features View full abstract»

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  • Magnetic and Read–Write Properties of Coupled Granular/Continuous Perpendicular Recording Media and Magnetization Reversal Process

    Page(s): 671 - 675
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    Coupled granular/continuous (CGC) media are formed by depositing a 6 nm Co/Pd multilayer onto a CoCrPt-SiO2 granular magnetic layer. The multilayer reduces magnetic saturation field Hs from 11.4 to 7.2 kOe. The lower Hs is reflected in the recording overwrite (OW) improvement of around 20 dB. The thermal stability factor KuV/kBT also increases with addition of the multilayer, from 60 to 100, resulting in the improvement of thermal stability for CGC media. The origin of the KuV/k BT increase derives from the larger activation volume. The CGC media has coherent magnetization reversal and very weak exchange coupling, similar to the base granular media. The coherent magnetization reversal with very weak exchange coupling contributes to a signal-to-noise-ratio (SNR) improvement of around 1 dB. These results suggest that CGC media have a recording advantage over the conventional structure media, and are a promising approach to avoid the limitations of the "magnetic recording tri-lemma" and realize future ultrahigh density recording media View full abstract»

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  • Issues in Recording Exchange Coupled Composite Media

    Page(s): 676 - 681
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    Exchange coupled composite (ECC) media exhibits a lower switching field than conventional perpendicular media at the same level of thermal stability, and thus is able to achieve higher areal density. The inhomogeneity of ECC media is predicted to enhance the thermal attempt frequency: this increases both writability and adjacent track erasure (ATE). The adverse change in ATE is, however, countered by the angular dependence of the ECC media switching field. This angular dependence is further exploited with a head design featuring a larger pole width than track width and the introduction of notches in the down track direction. This reduces the effect of head skew and increases the write field. An optimized head is found to be consistent with terabit/in2 recording View full abstract»

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  • Fabrication and Characterization of Exchange Coupled Composite Media

    Page(s): 682 - 686
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    Magnetic hard and soft phases CoCrPt-SiO2 thin films were developed to fabricate exchange coupled composite (ECC) media. Domain wall nucleation and propagation from the soft regions to the hard regions in the composite grains was found to be the switching mechanism in the ECC media. ECC media on the disk substrate with soft underlayer was fabricated. Interlayer thickness dependence of saturation field and domain wall length in CoCrPt-SiO2 soft layer suggested that domain wall nucleation and propagation in ECC media. Spin-stand testing showed more than a six-times reduction of saturation writing current and more than a 10 dB increase of total signal-to-noise ratio (SNR) for ECC media. Time decay results of readback signals indicated that there is no thermal stability problem for ECC media. The roll-off curve of ECC media showed the same SNR level as a state-of-art reference perpendicular media targeted around 200 Gb/in2. With further optimizations, areal densities beyond 1 Tb/in2 seem achievable for ECC media View full abstract»

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  • Micromagnetics of Percolated Perpendicular Media

    Page(s): 687 - 692
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    In this paper, we present a systematic micromagnetic analysis on the magnetic properties, thermal magnetic stability, and recording performance of percolated perpendicular media (PPM), a novel film microstructure of exchange coupled small-size magnetic grains with densely distributed nonmagnetic pinning sites. The analysis shows that the PPM microstructure can substantially reduce medium noise over the conventional granular perpendicular media while maintaining sufficient magnetic stability View full abstract»

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  • Fabrication, Microstructure, Magnetic, and Recording Properties of Percolated Perpendicular Media

    Page(s): 693 - 697
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    In this paper, a new type of perpendicular magnetic media which we have termed percolated perpendicular media is discussed. We present the method we used to fabricate the media as well as an energetic rationale for the driving force to produce the desired microstructure. The microstructures of samples with various amounts of oxide material are presented and the optimum one for our investigation is presented. We also present some preliminary drag test data that can be used to evaluate the recording properties of this media View full abstract»

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  • 2.5-mm-Thick 10 GB Hard Disk Drive Using 1-inch Single Side Perpendicular Recording

    Page(s): 698 - 703
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    A 2.5-mm-thick head disk assembly (HDA) was made for a capacity of 10 GB using 1-inch single-side perpendicular magnetic recording. Two types of chassis were prepared for investigating capability. All devices were assembled within 2.5 mm thickness on a sufficiently thick base for a block-type HDA, and devices were also assembled on 2.5-mm-thick pressed chassis for a card-type HDA. A 2.4-mm-thick fluid dynamic bearing spindle motor was used for both types of HDAs. The top cover of the chassis was screwed to the fixed central shaft of the spindle motor to ensure the mechanical stability of the card-type HDA. A thin pivot bearing was developed for the HDA. Mechanical simulation revealed that mechanical stability in a 2.5-mm-thick HDA is by no means inferior to that in 5-mm-thick HDA. The areal density of 200 Gb/in2 was found in a spin stand using CoCrPt-SiO2-based a perpendicular medium and a TuMR magnetic head. A new servo track writer was developed for thin HDAs using highly accurate laser scales. A servo signal with a track pitch of 100 nm (250 kTPI) was written on a block-type HDA. Track-pitch positioning accuracy of plusmn7% was achieved at a track pitch of 150 nm (169 kTPI) for both types of HDAs. Write and read performance was investigated in the hard disk assembly combined with printed circuit board View full abstract»

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  • Perpendicular Magnetic Recording Integration and Robust Design

    Page(s): 704 - 708
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    We have investigated the effects of stray magnetic field upon a perpendicular magnetic recording (PMR) system, which consists of a single pole type head and a double-layered perpendicular medium. We found that fields in the plane of the disk could cause serious erasure. External magnetic flux concentrates around the edges of a return pole and can cause very large fields to appear in the medium. In addition, the writing operation significantly enhances this erasure. We called this kind of erasure "corner erasure." Experimental 2.5-inch hard disk drives (HDDs) were used to study the combined effect of the external field and write field. We checked SER degradation after applying an in-plane field of 0.8 kA/m (10 Oe). With no write-current applied, there is no degradation. However, as little as 0.8 kA/m (10 Oe) applied during writing causes severe degradation equivalent to that produced by a 4.0 kA/m (50 Oe) field applied when the head is reading on-track. It is concluded that the realization of PMR in commercial HDD would require new transducer designs to solve these problems. We devised a new return pole design which has a stepped-back wing to improve the robustness against in-plane stray fields. The alternative design greatly reduces the concentration of magnetic flux at the edges of return pole. Consequently, the stepped wing structure achieves about twice the robustness of the conventional rectangular return pole. A method was developed to allow external field sensitivity to be carefully checked. The method allows the degraded areas of data to be associated with the exact feature on the head that caused the problem 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