Waltman R.J.,HGST Western Digital Company
Tribology Online | Year: 2014
Infrared specular reflection spectra of the TA-30, D-4OH and C4-4OH perfluoropolyether liquid films on gold substrates are simulated and studied experimentally. The simulated spectra were obtained using a classical dispersion analysis coupled with solutions of Maxwell's equations for transmission and reflection of electromagnetic radiation. The simulated spectra, which are based on a randomly oriented sample, provide excellent fits for the perfluoropolyethers over a wide film thickness range. Spectroscopic data are provided for TA-30, D-4OH and C4-4OH. The differences in the transverse and longitudinal optical IR spectra are discussed for off-normal reflection spectra in the thin film limit. Corrections to the IR reflection spectra for sub-monolayer coverage using effective medium theory are also discussed. © 2014 Japanese Society of Tribologists.
Waltman R.,HGST Western Digital Company
Tribology Online | Year: 2014
The D-4OH adsorbed film structure is investigated as a function of film thickness and of molecular weight via surface energy measurements, terraced flow profiles, and ellipsometric imaging for film dewetting. The D-4OH monolayer thickness on a carbon surface exhibited a power law dependence on molecular weight, where the exponent was determined to be 0.70. With decreasing film thickness, the in-plane component of the radius of gyration, normalized to the bulk radius of gyration, increased to ~ 1.5, consistent with an ellipsoidal conformation on the carbon surface. Confinement effects increased with increasing molecular weight. Copyright © 2014 Japanese Society of Tribologists.
Kilic U.,Bogazici University |
Kilic U.,Istanbul Bilgi University |
Finocchio G.,Messina University |
Hauet T.,CNRS Jean Lamour Institute |
And 3 more authors.
Applied Physics Letters | Year: 2012
High-temperature (near Curie-point) magnetization-behavior in materials with strong-perpendicular-magnetocrystalline-anisotropy has recently gained importance due to potential applications in thermally/heat-assisted-magnetic- recording (TAR/HAMR) systems. We have implemented a macrospin-model within the Landau-Lifshitz-Bloch formalism for strongly exchange-coupled CoNi/Pd multilayers subject to nanosecond-scale localized-heat and magnetic-field pulses. The temperature dependence of the longitudinal-susceptibility, as determined from a single-fitting-parameter of the experimental coercive-field, is consistent with the previously reported ab initio calculations. We demonstrate that this model is able to predict the full map of switching-speed as a function of magnetic-field and local-temperature providing a robust tool for the evaluation of this and similar material systems in TAR/HAMR applications. © 2012 American Institute of Physics.
Waltman R.,HGST Western Digital Company |
Wiita C.,HGST Western Digital Company
Tribology Online | Year: 2015
The interfacial properties of perfluoropolyether (PFPE) films having the [(CF2)nO] main chain with n = 1.5, 3 and 4, were systematically compared on carbon surfaces. The monolayer thickness decreases with increasing n, indicating that stiffer chains (larger n) lie flatter on the surface. The surface energy-derived disjoining pressure also increased with increasing n. Spin-stand tribological experiments indicated that clearance (slider-disk spacing) increased and PFPE lubricant pick-up decreased with increasing disjoining pressure and main chain stiffness. Slider wear rate increased with decreasing PFPE coverage and increasing main chain stiffness. Structure-property correlations are developed and discussed. Copyright © 2015 Japanese Society of Tribologists.