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Magnetics, IEEE Transactions on

Issue 1  Part 1 • Date Jan. 2011

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  • [Front cover]

    Publication Year: 2011 , Page(s): C1
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  • IEEE Transactions on Magnetics publication information

    Publication Year: 2011 , Page(s): C2
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  • Table of contents

    Publication Year: 2011 , Page(s): 1 - 2
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  • Chairman's Preface

    Publication Year: 2011 , Page(s): 3
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  • Message from the Publications Co-Chairs

    Publication Year: 2011 , Page(s): 4
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  • The 21st Magnetic Recording Conference (TMRC 2010)

    Publication Year: 2011 , Page(s): 5
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  • High-Density Bit Patterned Media: Magnetic Design and Recording Performance

    Publication Year: 2011 , Page(s): 6 - 10
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1664 KB) |  | HTML iconHTML  

    We examine the magnetic properties and recording performance of bit patterned exchange coupled composite (ECC) magnetic media at different bit and island aspect ratios. The ECC media consists of Co/Pd and Co/Ni multilayers whose coupling is controlled using Pd interlayers. We show that this multilayer system can be tuned to provide writeable media with a low switching field distribution for bit patterned magnetic recording. The recording performance of 100 Gb/in2 media shows a sub 1e-4 bit error rate floor and misregistration errors that are well-described by a simple error model. View full abstract»

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  • Write Margin Improvement in Bit Patterned Media With Inclined Anisotropy at High Areal Densities

    Publication Year: 2011 , Page(s): 11 - 17
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1551 KB) |  | HTML iconHTML  

    Bit patterned media with inclined anisotropy were proposed along with media design with a higher saturation magnetization and a small thickness for the dot. Inclination of the anisotropy axis was found to reduce broadened switching field distribution of the media caused by the magnetostatic interaction between the dots. Recording simulation at an areal density of 2.6 Tbit/in2 using a write field of a shielded planar head exhibited substantially increased write shift margins of 6.5 nm and 10 nm in down- and cross track directions, respectively, for the media with inclined anisotropy when the anisotropy dispersion of the media was as small as 2%. Recording density was expected to be increased beyond 4 Tbit/in2 for the media with additional exchange coupling between the dots. View full abstract»

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  • Reversal in Bit Patterned Media With Vertical and Lateral Exchange

    Publication Year: 2011 , Page(s): 18 - 25
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1148 KB) |  | HTML iconHTML  

    The extent to which dipolar interactions affect switching field distributions and thermal stability, and subsequently system performance, depends closely on the areal density, materials properties, and the architecture of the media, as well as the recording scheme and field profiles. This paper assesses, via micromagnetic simulations, the potential of heterogeneous capped bit patterned media and other proposed patterned media designs for ultra-high-density magnetic recording with respect to writability, switching field distributions, and thermal stability at different areal densities. Such media is comprised of an array of homogeneous or exchange coupled composite elements with vertical anisotropy that is ferromagnetically or antiferromagnetically coupled to a continuous horizontal layer. It is shown that such systems, characterized by lateral and vertical exchange, enable ultra-high-density recording at low switching fields while ensuring high thermal stability and low switching field distributions. Mechanisms leading to improved performance in capped systems are investigated. Structural and material considerations are provided for all media models. View full abstract»

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  • Statistical Modeling of Write Error Rates in Bit Patterned Media for 10 \hbox {Tb/\in}^{2} Recording

    Publication Year: 2011 , Page(s): 26 - 34
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (890 KB) |  | HTML iconHTML  

    A crucial issue for bit patterned media recording is write-errors. This is an essential concern for media whose individual bits are represented by single switching units (dots) due to the insufficient writing field gradient at high areal densities. In this paper a statistical approach to clarify the write error rate for a system with a switching field distribution and a head field gradient is established using binomial distribution modeling. Then, two approaches to reduce the write error rate are presented. The first is multi-dot recording with a bit patterned structure, in which the error rate is reduced due to the averaging effect of recording on several dots. The switching field distribution can also be reduced if exchange coupling is introduced between the dots. The second possible approach is the combination of bit patterned media and temperature gradient recording. This effectively improves the writing gradient. The minimum bit length and achievable areal density is estimated taking into account the switching field distribution and writing field gradient. View full abstract»

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  • Write Channel Model for Bit-Patterned Media Recording

    Publication Year: 2011 , Page(s): 35 - 45
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (807 KB) |  | HTML iconHTML  

    We propose a new write channel model for bit-patterned media recording that reflects the data dependence of write synchronization errors. It is shown that this model accommodates both substitution-like errors and insertion-deletion errors whose statistics are determined by an underlying channel state process. We study information theoretic properties of the write channel model, including the capacity, symmetric information rate, Markov-1 rate, and the zero-error capacity. View full abstract»

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  • Dynamic Fly Performance of Air Bearing Sliders on Patterned Media

    Publication Year: 2011 , Page(s): 46 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1479 KB) |  | HTML iconHTML  

    It is anticipated that a radical shift in design paradigm will be required in order to enable perpendicular magnetic recording (PMR) areal densities beyond 1 Tb/in2 . The shift in question will involve the use of advanced magnetic recording assist technologies such as patterned media, heat-assisted magnetic recording (HAMR), or microwave-assisted magnetic recording (MAMR). This paper is concerned with one of the challenges associated with the practical implementation of patterned media technology, namely, the impact of non-planarity, and shifts in pattern orientation (at data-servo transitions, in particular) on the dynamic fly performance of air bearing sliders. The nature of the latter challenge becomes apparent when considering that key to realizing recording areal densities exceeding 1 Tb/in2 will be air bearing sliders with superior dynamic fly stability at sub-2 nm clearances. Of the two types of patterned media technologies in development in the disk drive industry, namely, discrete track media (DTM) and bit patterned media (BPM), the former was chosen as a case study in this work. View full abstract»

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  • Fabrication of Ridge-and-Groove Servo Pattern Consisting of Self-Assembled Dots for 2.5 \hbox {Tb/\in}^{2} Bit Patterned Media

    Publication Year: 2011 , Page(s): 51 - 54
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1094 KB) |  | HTML iconHTML  

    Bit patterned media (BPM) is fabricated by a directed self-assembled polymer mask. CoPt magnetic dots with 17 nm pitch (2.5 Tb/in2) consists of ridge-and-groove servo patterns as well as circular data tracks. Distribution of dot size and dot pitch is 16% and 15%, respectively. The position error signal (PES) is estimated numerically employing a simulation model using estimated deviation of dot size and pitch. PES linearity was found to be fairly good in spite of large dot pitch deviation. Distribution of dot size and dot pitch causes distortion in the reproduced waveform, but it does not degrade the phase information of the servo signal. This result indicates that the ridge-and-groove servo has a high tolerance to the amplitude noise and is suitable for BPM. When the width of the read head is close to the dot pitch, the linearity error increases owing to the dot size and dot pitch deviation. Reduction of these distributions is necessary in order to apply BPM to hard disk drives. View full abstract»

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  • Writeability Enhancement in Perpendicular Magnetic Multilayered Oxide Media for High Areal Density Recording

    Publication Year: 2011 , Page(s): 55 - 62
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1155 KB) |  | HTML iconHTML  

    A systematic investigation of the switching behavior and writeability characteristics of perpendicular magnetic oxide media was performed by varying the number of oxide layers as well as the anisotropy Ku gradient in multilayered oxides. The media switching behavior highly depends on the magnetic volume of laterally exchange-coupled cap layer as well as the vertical exchange coupling between oxide and cap layers. The media switching field is significantly reduced with incoherent switching mode. The media writeability is further enhanced by employing the multilayered oxides whose anisotropy values vary. Higher Ku graded oxide media exhibits improved resolution, sharper transition, and higher signal-to-noise ratio. An analytical 9-spin model is used to study the impact of anisotropy grading, intergranular and interlayer exchange coupling on writeability and noise performance. The 9-spin model is found to qualitatively agree with the experimental results. Both model and experiment indicate that optimal tuning of the media anisotropy and exchange to the head design is critical in attaining good recording performance. View full abstract»

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  • Effect of Composite Designs on Writability and Thermal Stability of Perpendicular Recording Media

    Publication Year: 2011 , Page(s): 63 - 68
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    The function of two types of magnetic inhomogeneity employed in perpendicular magnetic recording media designs are analyzed. Continuous granular composite (CGC) media have variable lateral exchange coupling (Hex) through the thickness of the magnetic layers, which can reduce coercivity (Hc) and narrow switching field distribution (SFD). Exchange coupled composite (ECC) media have variable crystalline anisotropy field (Hk) and interlayer exchange coupling (J) through the film thickness, which also reduces Hc. Interactions between the Hk, Hex, and J values of combined ECC+CGC media are presented. The optimum anisotropy profile for conventional ECC media is found to be different than previously modeled. A CGC layer included in the ECC media architecture is shown to change the optimal anisotropy profile and interlayer coupling values. View full abstract»

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  • Magnetic Damage and Performance Recovery in Discrete Track Media

    Publication Year: 2011 , Page(s): 69 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1042 KB) |  | HTML iconHTML  

    Discrete track media (DTM) has been widely studied recently as a solution to achieve high track density for hard disk drives. In DTM, nano-patterning process is used to isolate magnetic tracks. During the fabrication process, magnetic damage occurs in the resist striping process using O2 plasma. The on-track SNR of DTM degrades by ~ 2-3 dB. We used Ar IBE cleaning process to remove the oxide layer. The removal process induces unexpected magnetic property change. Nevertheless, this process can still improve the SNR significantly. However, the cleaning step also causes track corner rounding, and results in a faster SNR roll-off at high linear densities. Several methods for further improving DTM performance are discussed in this paper, including using a protective cap layer and media magnetic design reoptimization. View full abstract»

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  • Noise Mechanisms in Small Grain Size Perpendicular Thin Film Media

    Publication Year: 2011 , Page(s): 74 - 80
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1700 KB) |  | HTML iconHTML  

    In this paper, we present a set of systematic experimental investigations on possible noise mechanisms for current perpendicular thin film media of small grain sizes. In particular, we focus on intergranular exchange coupling and grain boundary surface anisotropy in the granular layer of the present continuous-granular-composite film structure. Micromagnetic modeling studies are conducted to study the impact of the observed experimental phenomenon. Modeled experiments show that significant intergranular exchange coupling may occur when oxide grain boundary thickness becomes less than 1 nm. If the grain boundary thickness has significant distribution below this critical value, the exponential dependence of the coupling strength on the oxide thickness would yield significant degradation of the medium signal-to-noise ratio. Carefully designed experiments have also been conducted to study possible grain boundary interfacial anisotropy. Co/Cr, CoPt/Cr, Co/SiO2, Co/Cr2O3, and Co/TiO 2 interfaces are investigated and the corresponding interfacial anisotropy strengths are quantitatively measured. Although Co/SiO2 interfacial anisotropy appears to be the weakest among them, the measured interfacial anisotropy energy strengths for all of them are significant fractions of the crystalline perpendicular anisotropy of the grains at present grain sizes. Finally, we investigated the impact of stacking faults in hcp Co-alloy grains. It is found that when the anisotropy strength of a small segment of a grain substantially reduces due to the existence of stacking faults, it will yield a switching field reduction disproportional to the volume ratio of the segment. View full abstract»

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  • Highly Ordered FePt L1_{0} Thin Films With Small Grains on RuAl Seed Layers

    Publication Year: 2011 , Page(s): 81 - 86
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1219 KB) |  | HTML iconHTML  

    We present an experimental approach for obtaining highly ordered L10 FePt-oxide thin film media with small grains by using a RuAl layer as a grain size defining underlayer. In most previous studies, the FePt grain size was controlled by tuning the oxide volume fraction of the film. By introducing the RuAl grain size defining layer, 6 nm of FePt grains can be obtained at 520°C with 9% SiO2 in the film. A 5 nm thin barrier layer was introduced between FePt and RuAl to prevent the inter-diffusion between RuAl and FePt. The influence of different barrier layers was studied. With a thin Ag sacrificial layer inserted between the barrier layer and the FePt magnetic layer, a smaller grain size can be achieved, the ordering temperature was lowered, and the (001) texture of FePt was enhanced. View full abstract»

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  • Hierarchical Multiscale Modeling Method for Head/Disk Interface

    Publication Year: 2011 , Page(s): 87 - 93
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (719 KB) |  | HTML iconHTML  

    Multiscale modeling opens a new paradigm by providing a novel methodology of establishing molecular design criteria and potentially gives several orders of magnitude advances in nanotechnology. The head/disk interface (HDI) in the hard disk drive system investigated here can be used as a benchmark for multiscale modeling. Our approach, stemmed from the novel middle-out approach in modern multiscale modeling using the lattice Boltzmann method (LBM) as the centerpiece formulation, marches towards continuum level (top) and molecular level (bottom). This approach will become an extremely valuable tool in generating design criteria of HDI. View full abstract»

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  • Effect of Ultraviolet Irradiation on Adhesion of Nanometer-Thick Lubricant Films Coated on Magnetic Disk Surfaces

    Publication Year: 2011 , Page(s): 94 - 99
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (209 KB) |  | HTML iconHTML  

    By measuring force-distance curves with an environmental scanning probe microscope (SPM), we quantitatively evaluated the effect of ultraviolet (UV) irradiation on the adhesive properties of nanometer-thick perfluoropolyether (PFPE) Z03 films coated on magnetic disks. The experimental results indicated that UV irradiation shows negligible influence on the adhesion of the disk surface and on the adhesion of the mobile fraction contained in the UV-irradiated Z03 films. The effect of UV irradiation on the adhesion of Z03 films is essentially achieved by its effect that improves the bonding of the Z03 molecules to the disk surfaces. As the bonding ratio increased with UV irradiation, the adhesive force measured on the 2-nm-thick PFPE Z03 films initially decreased, but it increased after reaching a minimum at a bonding ratio of about 0.6. This is possibly attributed to the increase of the meniscus force caused by decreased mobile lubricant thickness and the decrease of the van der Waals force between the SPM probe and the sample surfaces caused by increased bonded lubricant thickness. View full abstract»

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  • Thermal Flying-Height Control Sliders in Air-Helium Gas Mixtures

    Publication Year: 2011 , Page(s): 100 - 104
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    Filling hard disk drives with air-helium gas mixtures instead of pure helium can balance performance improvement, such as reduced power cost, increased capacity and improved reliability, against manufacturing cost increase. A consistent approach is proposed here to investigate the flying performance of thermal flying height control sliders flying in air-helium gas mixtures. It is found that the smallest power required for a designated flying height appears when the gas mixture is composed of about half helium and half air. The proposed numerical approach can also find application in investigating a slider's flying performance in a humid environment. View full abstract»

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  • Lubricant Depletion Characteristics Induced by Rapid Laser Heating in Thermally Assisted Magnetic Recording

    Publication Year: 2011 , Page(s): 105 - 110
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (930 KB) |  | HTML iconHTML  

    In this study, fundamental research was conducted on lubricant depletion due to rapid laser heating in thermally assisted magnetic recording (TAMR) systems. The effects of lubricant film thickness on lubricant depletion were investigated using a conventional lubricant, Zdol2000. The lubricant depletion characteristics resulting from laser heating were found to largely depend on the lubricant film thickness. Lubricant depletion mechanisms were also studied. In this study, it was found that lubricant depletion is predominantly due to lubricant evaporation for cases in which the lubricant film thickness is greater than one monolayer. In addition, the effect of laser irradiation duration on lubricant depletion was investigated using both continuous and 300-kHz pulsed laser irradiations, since actual TAMR systems require pulsed laser irradiation lasting a few nanoseconds. The differences between the fundamental lubricant depletion characteristics of continuous and pulsed laser irradiations were elucidated on the basis of the experimental results obtained in this study. Furthermore, it has been suggested that diamond-like-carbon (DLC) thin films on the disk surfaces are also affected by rapid laser heating, because the temperature of the films increases to more than 500 K upon laser heating. Therefore, we also studied the damage to DLC thin films due to rapid laser heating and found that the reflectivity of the DLC thin films changed; this change was presumably due to the decrease in the DLC density as well as the asperity in the laser-irradiated region. View full abstract»

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  • Tribological and Dynamic Study of Head Disk Interface at Sub-1-nm Clearance

    Publication Year: 2011 , Page(s): 111 - 116
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1281 KB) |  | HTML iconHTML  

    As the areal recording density approaches to 1 Tb/in2, the spacing between magnetic heads and medium is decreased to sub-1-nm regime with the application of dynamic flying height (DFH) technology. Challenges in tribological flyability and reliability in the head-disk interface (HDI) become formidable at such ultra-low spacing, and it is necessary to achieve from both media and head design. It is also essential to have a better touch-down (TD) detection method and more accurate back-off spacing control for sustainable tribological performances. In this paper, the dynamics and wear during TD process were studied first. The characteristic TD modes were identified by laser Doppler vibrometry (LDV) and the TD induced wear was quantified using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that different TD stages correspond to different TD modes and amount of TD wear. It is found that the identification and capture of the characteristic TD modes, especially the first TD mode, are the key factors to timely detect TD and minimize the TD wear. The tribological performances at sub-1-nm clearance were then investigated with respect to both head and media design. The slider dynamics over a bump was studied to simulate the head reliability when the head intermittently contacts the media. It is found that air bearing surface (ABS) design of the head has a significant influence on the settling time when head passes through the bump. In addition, the flyability over a wavy surface (i.e., media run-out) was also studied to understand the TD repeatability. The results show that media run-out strongly affects TD repeatability and back-off spacing accuracy. Consequently, spacing control to sustain the reliability at sub-l-nm clearance is necessary. With in-depth understanding of dynamics and tribological performances (i.e., flyability and reliability), media and head ABS design are the key factors to achieve a sustainable HDI at sub-1- - -nm clearance. View full abstract»

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  • Experimental Study of Head-Disk Interface Instability on Light Contact Recording Using Dynamic Flying Height Control

    Publication Year: 2011 , Page(s): 117 - 123
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1101 KB) |  | HTML iconHTML  

    The instability of the slider touchdown process was observed by the sensitive method that uses PZT ((Zrx Ti1 - x) O3 ) sensor mounted on a suspension. By using this method, we could differentiate from the contact between the slider and the lubricant surface, the stable regime beyond touchdown (surfing regime), and the final full contact with the disk surface. Z-dol2000S clearly showed the surfing regime, but Z-tetraol2000S did not show the surfing regime on a thin lubricant film with a thickness of less than 16 Å. In the case of Z-dol, the magnitude of the slider vibration at the contact on the lubricant surface depended on the lubricant thickness; in the case of Z-tetraol, a large vibration was observed only at 20 Å. We have tried to explain these phenomena with the help of potential energy curves that are based on intermolecular forces calculated by molecular dynamic simulations. Potential energy curves could be used to explain the stability of the touchdown process. View full abstract»

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  • Taking a Fresh Look at Disjoining Pressure of Lubricants at Slider-Disk Interfaces

    Publication Year: 2011 , Page(s): 124 - 130
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB) |  | HTML iconHTML  

    As the clearances in disk drives approach subnanometer values, accurately predicting lubricant behavior is becoming more critical to designing reliable slider-disk interfaces. Central to any analysis of lubricant in disk drives is the disjoining pressure of the lubricant films on the disk and slider surfaces. This paper reviews current measurement techniques of the disjoining pressure of the lubricants used in disk drives and theoretical expressions of the disjoining pressure as a function of lubricant thickness. This paper also discusses what disjoining pressure analyses will be needed for future disk drive technologies. 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