Hitachi San Jose Research Center

Hayward, CA, United States

Hitachi San Jose Research Center

Hayward, CA, United States

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Hofmann T.,Brookhaven National Laboratory | Tasinkevych M.,Max Planck Institute for Intelligent Systems (Stuttgart) | Tasinkevych M.,University of Stuttgart | Checco A.,Brookhaven National Laboratory | And 4 more authors.
Physical Review Letters | Year: 2010

The wetting by perfluoromethylcyclohexane of a well-defined silicon grating with a channel width of 16 nm has been studied using transmission small angle x-ray scattering. Prefilling, capillary filling, and postfilling wetting regimes have been identified. A detailed comparison of the data with theory reveals the importance of long-ranged substrate-fluid and fluid-fluid interactions for determining the wetting behavior on these length scales, especially at the onset of capillary condensation and in the prefilling regime. © 2010 The American Physical Society.


Kalezhi J.,University of Manchester | Kalezhi J.,Copperbelt University | Greaves S.J.,Tohoku University | Kanai Y.,Niigata Institute of Technology | And 3 more authors.
Journal of Applied Physics | Year: 2012

In bit patterned media (BPM), a magnetic data storage medium is patterned into nanoscale magnetic islands each representing one binary digit (bit). The recording performance of BPM depends upon the variability of island position, geometry, and magnetic characteristics. To understand the impact of the distributions of these parameters on the performance of BPM a detailed statistical model of write-errors has been developed. The islands can either be single layer or two-layer exchange coupled composite (ECC) structures. The modeling of ECC islands was made possible by the development of a 2-spin model to calculate switching field, coercivity, and energy barrier as a function of applied field which enables medium design to be optimized for a non-uniform write head field. The statistical model predicts coercivities and error rates in good agreement with a micromagnetic model but at significantly lower implementation and computational cost and shows good agreement with experimental data from drag-test experiments at 500 Gbit/in 2. The model enables the position tolerance of the write head to be determined from the magnetic characteristics of the write head and the storage medium and it is therefore a valuable system design tool. © 2012 American Institute of Physics.


Briones J.,CNRS Jean Lamour Institute | Montaigne F.,CNRS Jean Lamour Institute | Hehn M.,CNRS Jean Lamour Institute | Lacour D.,CNRS Jean Lamour Institute | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We study the thermally induced depinning process of a single magnetic domain wall (DW) under applied field when the DW is trapped by a notch made in a nanowire shaped from a spin-valve multilayer with in-plane magnetization. In such devices depinning is typically a stochastic process and the depinning field distribution exhibits complex features. By analyzing simultaneously depinning field distributions and relaxation data, we observe two distinct sources of "complexity" in DW depinning processes: multiplicity in the DW structure and fundamental complexity in the depinning process. © 2011 American Physical Society.


Listera S.J.,University of St. Andrews | Kohlbrecher J.,Paul Scherrer Institute | Venkataramanaa V.,University of St. Andrews | Thomsonc T.,University of Manchester | And 2 more authors.
International Journal of Materials Research | Year: 2011

Perpendicular magnetic recording media based on CoCrPt-SiO x thin-films have been studied with polarised small angle neutron scattering (SANSPOL) to probe the local (sub-10nm) granular structure and its magnetisation distribution. SANSPOL is sensitive to the direction of the magnetisation vector in the grains over a size range of 1-100 nm. This allows the grain size dependent magnetic reversal process to be probed in the recording layer. SANSPOL data can be analysed both using numerical models and through comparison with the granular structure determined using transmission electron microscopy. In this paper we compare these two methods in detail and demonstrate that both approaches arrive at very similar conclusions. © 2011 Carl Hanser Verlag, Munich, Germany.


Lister S.J.,University of St. Andrews | Thomson T.,University of Manchester | Kohlbrecher J.,Paul Scherrer Institute | Takano K.,Hitachi San Jose Research Center | And 7 more authors.
Applied Physics Letters | Year: 2010

Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt-SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter. © 2010 American Institute of Physics.


Carey M.J.,Hitachi San Jose Research Center | Maat S.,Hitachi San Jose Research Center | Chandrashekariaih S.,Hitachi San Jose Research Center | Katine J.A.,Hitachi San Jose Research Center | And 3 more authors.
Journal of Applied Physics | Year: 2011

Magnetic and magnetotransport properties of current-perpendicular-to-the- plane (CPP) giant-magnetoresistance (GMR) spin-valve sensors containing the Heusler alloy Co2MnGe are presented. The geometrical and head integration constraints which exist for recording head applications are discussed and dictate various design compromises which determine the final device properties. Here we show that even for small total sensor thicknesses 400 Å and anneal temperatures ≤250° we can obtain CPP-GMR signal levels up to δRA 4 mω-μm2 at room temperature when inserting Co2MnGe in both the free layer and reference layers of the spin valve. Output levels increase to 10 mω-μm2 when reducing the temperature below 100 K, demonstrating the strong temperature dependence of the spin-dependent scattering in the Co2MnGe-based magnetic layers. © 2011 American Institute of Physics.


Lille J.,Hitachi San Jose Research Center | Patel K.,Hitachi San Jose Research Center | Ruiz R.,Hitachi San Jose Research Center | Wu T.-W.,Hitachi San Jose Research Center | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Bit patterned media (BPM) for magnetic recording has emerged as a promising technology to deliver thermally stable magnetic storage at densities beyond 1Tb/in2. Insertion of BPM into hard disk drives will require the introduction of nanoimprint lithography and other nanofabrication processes for the first time. In this work, we focus on nanoimprint and nanofabrication challenges that are being overcome in order to produce patterned media. Patterned media has created the need for new tools and processes, such as an advanced rotary e-beam lithography tool and block copolymer integration. The integration of block copolymer is through the use of a chemical contrast pattern on the substrate which guides the alignment of di-block copolymers. Most of the work on directed self assembly for patterned media applications has, until recently, concentrated on the formation of circular dot patterns in a hexagonal close packed lattice. However, interactions between the read head and media favor a bit aspect ratio (BAR) greater than one. This design constraint has motivated new approaches for using self-assembly to create suitable high-BAR master patterns and has implications for template fabrication. © 2011 SPIE.


Mosendz O.,Hitachi San Jose Research Center | Pisana S.,Hitachi San Jose Research Center | Reiner J.W.,Hitachi San Jose Research Center | Stipe B.,Hitachi San Jose Research Center | Weller D.,Hitachi San Jose Research Center
Journal of Applied Physics | Year: 2012

Thermally assisted magnetic recording (TAR), a promising approach to extend data storage densities beyond 1 terabit/in. 2, requires high anisotropy granular magnetic media with small grains and a tight grain size distribution. We demonstrate sputtered chemically ordered granular L1 0 Fe 45Pt 45Ag 10 media using carbon segregant on glass substrates. X-ray diffraction and transmission electron microscopy reveal high chemical ordering, an average grain size of D 7.2 nm and a size distribution as low as σ D / D = 16 %. Magnetic properties studied with a vibrating sample magnetometer show H c 4.8 T, H k > 9 T, and K u > 4.5 × 10 7 erg/cm 3. Drag testing of this media shows recording areal densities of 620 Gb/in. 2. © 2012 American Institute of Physics.


Lille J.,Hitachi San Jose Research Center | Ruiz R.,Hitachi San Jose Research Center | Wan L.,Hitachi San Jose Research Center | Gao H.,Hitachi San Jose Research Center | And 7 more authors.
IEEE Transactions on Magnetics | Year: 2012

Magnetic recording bit patterned media (BPM) stands as a promising technology to deliver thermally stable magnetic storage at densities beyond 1 Tb/in 2. High throughput BPM fabrication will be enabled by nanoimprint lithography which relies on a high-quality master template to be able to meet pattern fidelity and low defectivity specifications. Master template fabrication for BPM can be done by e-beam lithography alone or by e-beam directed self-assembly of block copolymers. Incorporating servo features in the fabrication of master templates brings numerous nanofabrication challenges that vary depending on which method is used. Here we demonstrate the fabrication of conventional servo features at 200 Gd/in 2 using e-beam lithography and we explore some nonconventional servo geometries that are compatible with self-assembly for BPM beyond 1 Td/in 2. © 2012 IEEE.


Mate C.M.,Hitachi San Jose Research Center | Marchon B.,Hitachi San Jose Research Center | Murthy A.N.,CA Technologies | Kim S.-H.,CA Technologies
Tribology Letters | Year: 2010

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased slider-disk spacing during disk drive operations. This is done using both a new experimental methodology, called the "droplet stress test," and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider. © 2009 Springer Science+Business Media, LLC.

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