Parkway, CA, United States
Parkway, CA, United States

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Quinsat M.,CEA Grenoble | Tiberkevich V.,Oakland University | Gusakova D.,CEA Grenoble | Slavin A.,Oakland University | And 7 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In an isochronous auto-oscillator, where the auto-oscillation frequency f does not depend on the oscillation amplitude, the linewidth of the nth harmonic is n2 times larger than the linewidth of the main auto-oscillation mode. Here we present a theoretical description that predicts that the increase in the linewidth of higher harmonics with harmonic number n is substantially slower in the case of a nonisoschronous oscillator, where f depends strongly on amplitude. Using spin-torque nano-oscillators as an example of a nonisochronous oscillator, this description is confirmed numerically and experimentally. The presented model allows one to extract important nonlinear parameters of an auto-oscillator of any physical nature from the measurement of higher harmonic linewidths. © 2012 American Physical Society.


Marchon B.,San Jose Research Center | Guo X.C.,San Jose Research Center | Canchi S.,San Jose Research Center | Wang R.H.,San Jose Research Center | And 7 more authors.
Tribology Letters | Year: 2012

Experimental data are presented, showing that the flying height of a slider in a hard disk drive can be altered by the chemical nature of the molecularly-thin lubricant film on the disk surface. It is suggested that this effect is likely due to entrapment of the air molecules, both nitrogen and oxygen, within the lubricant film, which results in pressurization loss within the air bearing gap, and lower slider flying height. For the two advanced multidentate lubricants reported in this study, the amount of flying height change is almost insignificant for one of them, but amount to about 0.7 nm, i.e. a significant fraction of the magnetic spacing budget for the other. Bulk air solubility data suggest that the magnitude of this effect is diminished for lubricant molecules with a lower density of backbone ether linkages. © Springer Science+Business Media, LLC 2012.


Li J.,Hitachi Ltd. | Xu J.,Hitachi Ltd. | Shimizu Y.,Hitachi Ltd. | Honchi M.,Hitachi GST | And 2 more authors.
Journal of Tribology | Year: 2010

Perturbation and modal-analysis methods were employed to systematically study a damped slider's dynamic characteristics, including an air-bearing slider's stiffness, damping coefficient, frequency response to translation and wavy motion, natural frequencies, damping ratios, and modal shape-node line. We found that a design with grooves distributed on a trailing pad effectively improved the slider's damping ratio in the second pitch mode; however, parametric studies revealed that the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider we designed with distributed damped grooves on a trailing pad had a higher damping ratio in the second pitch mode, and hence, its responses in the second pitch mode were greatly reduced, which were clarified through simulation and an experiment. Some issues on air-bearing stiffness reduction and negative damping at low frequency and contamination and lube pickup on the damped grooves were also evaluated in the experiment. No degradation could be found in the damped slider. © 2010 by ASME.


Li J.,Hitachi Ltd. | Xu J.,Hitachi Ltd. | Shimizu Y.,Hitachi Ltd. | Honchi M.,Hitachi GST | Ono K.,Hitachi Ltd.
Proceedings of the ASME/STLE International Joint Tribology Conference 2009, IJTC2009 | Year: 2010

Small perturbation and modal-analysis methods were employed to systematically study a damped slider's dynamic characteristics. We found that a design with grooves distributed on a trailing pad effectively improved the slider's damping at higher frequencies, and the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider with distributed damping grooves on a trailing pad had a higher damping ratio in the third mode, and hence, its responses to disk parallel and wavy motion were greatly reduced. This new design for the damped slider was an effective solution reducing the slider's modulation. © 2009 by ASME.


Waltman R.J.,Hitachi GST | Deng H.,Hitachi GST | Wang G.J.,Hitachi GST | Zhu H.,Hitachi GST | Tyndall G.W.,Ferrari
Tribology Letters | Year: 2010

Lubricant pick-up by a low-flying slider is investigated for hydroxyl-terminated perfluoropolyethers as a function of the number of hydroxyl (OH) groups and of film thickness on the surface of finished rigid disks. The total number of hydroxyl (OH) groups per main chain is 2, 4, and 8 for Zdol, Z-Tetraol, and ZTMD, respectively. The amount of disk lubricant that is picked up by the low-flying slider decreases with decreasing PFPE film thickness and increasing number of OH functional groups. The results are discussed in terms of the disjoining pressure characterizing the lubricant film on the disk surface. © 2010 Springer Science+Business Media, LLC.


Waltman R.J.,Hitachi GST | Guo X.-C.,Hitachi GST
Tribology Letters | Year: 2012

AFM force-distance curves on 10-Å films of Zdol, Z-Tetraol, and ZTMD were investigated using a carbon-modified AFM tip. The forces were non-specific dominated by adhesive and/or capillary forces. The snap-to distances for unbaked Zdol, Z-Tetraol, and ZTMD were 1.9, 1.0, and 0.8 nm, respectively, and decreased with increasing molecular polarity. ZTMD allowed the closest approach before snap-to, by approximately 1 nm. However, annealed samples showed an identical 1.6 nm snap-to distance, indicating that an identical perfluoropolyether backbone was presented to the AFM tip at the PFPE/air interface. The pull-out forces for unbaked Zdol, Z-Tetraol, and ZTMD were in the 15-40 nN range and increased with increasing molecular polarity and loading rate. After annealing, the pull-out forces for the baked Zdol, Z-Tetraol, and ZTMD were significantly reduced to 10-20 nN, indicating that the polar end groups were less involved by bonding to the underlying surface. Force-distance curves for single-chain unbinding and entropic elasticity were computed to be near 300 and <100 pN, respectively, indicating that the force-distance curves for the experimental tip-PFPE interactions originated from multiple PFPE interactions with the tip. © 2011 Springer Science+Business Media, LLC.


Waltman R.J.,Hitachi GST | Joseph J.,Hitachi GST | Guo X.-C.,Hitachi GST
Corrosion Science | Year: 2010

The corrosion susceptibility of a cobalt-based magnetic alloy as a function of overcoat film thickness at 20 °C and 50% relative humidity is investigated using atomic force microscopy. The overcoat films include ion beam-deposited nitrogenated carbon (IBDN), and sputter-deposited silicon carbide (SiC) and silicon nitride (SiNx). In all cases, corrosion decreases with increasing overcoat film thickness. The critical overcoat film thickness for corrosion inhibition is approximately 25, 25 and 20 Å for IBDN, SiC and SiNx, respectively. However, larger corrosion particles are found for IBDN and SiC with increasing thickness just below the critical thickness for coverage. © 2010 Elsevier Ltd. All rights reserved.


Ab initio quantum chemical computations on model perfluoropolyether (PFPE) boundary lubricant film structures are used to study the effect of main chain confinement on dynamic main chain expansion in the direction perpendicular to the underlying surface. The simulations are conducted on single-chain PFPE structures that contain a pendant branch in the middle of the main chain anchored to the underlying surface. Results indicate a substantial increase in the energy required to expand the branched chain compared to an identical but unbranched main chain. Conformational analyses as a function of main chain expansion indicate the removal of low energy torsional pathways in the branched main chain that could otherwise provide low energy pathways for conformational rearrangement to allow the main chain expansion. © 2011 Springer Science+Business Media, LLC.


Wood R.,Hitachi GST
IEEE Transactions on Magnetics | Year: 2012

Analytic expressions are derived in the 2D frequency-domain for the interaction between magnetized layers that lie between two sheets of soft magnetic material. For example, in writing and reading with perpendicular magnetic recording, a multilayer hard magnetic medium lies between the soft magnetic underlayer (SUL) of the medium and the soft structures (including shields) that form the read and write heads. The expression for the interaction between different layers is an extension of earlier work, however the derivation of the self-interaction of a single layer is novel as is the translation of these interactions into tensor form in Cartesian coordinates suitable for micromagnetic modeling. © 1965-2012 IEEE.


Waltman R.J.,Hitachi GST | Kobayashi N.,Matsumura Oil Research Corporation
Tribology Transactions | Year: 2011

The thin-film properties of some perfluoropolyether boundary lubricants based on hydroxyl-termination of the n-perfluoropropylene oxide monomer units are investigated as a function of molecular polarity. The n-perfluoropropylene oxide monomer units provide a stiffer main chain than perfluoropolyethers comprised of a copolymer of perfluoro-methylene oxide and -ethylene oxide monomer units. Terraced flow and bonding kinetics show that the stiffer main chain reduces lubricant mobility on the disk surface but provides a lower profile lubricant film. The lack of mobility attributed to the main chain can be compensated for by decreasing the number of OH end groups. The Hamaker constants, derived from surface energy vs. thickness measurements are larger than the corresponding flexible main chains, suggesting an increased adhesion to the underlying carbon surface.

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