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Gottwald M.,CNRS Jean Lamour Institute | Gottwald M.,Center for Magnetic Recording Research | Hehn M.,CNRS Jean Lamour Institute | Lacour D.,CNRS Jean Lamour Institute | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Magnetization reversal has been studied in a Co 74Tb 26/Cu/Co 88Tb 12 system, which is a perpendicularly magnetized ferrimagnetic bilayer separated by a nonmagnetic layer. The Co 88Tb 12 (soft) layer (SL) exhibits a switching field much lower than the Co 74Tb 26 (hard) layer (HL), which enabled us to study the magnetization reversal of the SL for different magnetic states of the HL. We found an asymmetric hysteresis loop for the SL, when the HL is not fully saturated. Using careful analysis of magnetic force microscopy measurements we conclude that the asymmetry originates from magnetic domains formed in the HL that affect the SL reversal. A simple model based on magnetic dipolar interaction between the two layers is found to be in good agreement with the experimental data. © 2012 American Physical Society. Source

Brunner R.,Center for Magnetic Recording Research | Tyndall G.W.,Ferrari | Waltman R.J.,CA Technologies | Talke F.E.,Center for Magnetic Recording Research
Tribology Letters | Year: 2010

The relationship between the adhesion of surfaces separated by a molecularly thin liquid film and the surface energy of the film was investigated. AFM-based force-distance curves were measured on a series of carbon surfaces coated with hydroxyl-terminated perfluoropolyether (PFPE) films. The surface energy of the PFPE films was varied by altering either the total film thickness or the bonding ratio of the film by changing the concentration of the PFPE film in the solution and/or the pull-rate during dip-coating. A linear relationship between adhesion force and surface energy was observed. Adhesion was found to vanish at non-zero values of surface energy. The experimental results indicate that the adhesive force between macroscopic bodies separated by molecularly thin liquid films is linearly proportional to the excess surface energy of the film. © 2010 The Author(s). Source

Qin M.,Center for Magnetic Recording Research | Yaakobi E.,Center for Magnetic Recording Research | Yaakobi E.,California Institute of Technology | Siegel P.H.,Center for Magnetic Recording Research
IEEE Transactions on Information Theory | Year: 2014

Multilevel flash memory contains blocks of cells that represent data by the amount of charge stored in them. The cell writing - or programming - process applies specified voltages in a sequential manner, injecting charge to achieve a desired level. Reducing a cell level requires a costly block erasure, so programming only increases cell levels. Parallel programming, whereby a common voltage is applied to a group of cells to inject charge simultaneously, simplifies circuitry and increases programming speed. However, cell-to-cell variations and limited programming round can adversely affect its precision. In this paper, we consider algorithms for efficient cell programming. Since cell levels are quantized to a discrete set of values, our objective is to minimize the number of cells that are not quantized to their target levels. For a specified number of programming rounds, we derive an optimal parallel programming algorithm with complexity that is polynomial in the number of cells. We extend the algorithm to account for intercell interference, where the voltage applied to a cell can affect the level of adjacent cells. We then consider noisy programming of a single cell, with and without feedback about the cell level. In both scenarios, we present an algorithm that, for a given number of programming rounds, minimizes the probability of an incorrect cell level. © 2014 IEEE. Source

Yoon Y.,Center for Magnetic Recording Research | Talke F.E.,Center for Magnetic Recording Research
Microsystem Technologies | Year: 2010

The touch-down and take-off characteristics of a typical pico-type magnetic recording slider is investigated as a function of pressure level and groove dimensions of discrete track recording (DTR) media. Keeping the ambient pressure constant, we found that the touch-down velocity was higher for DTR disks than for "smooth" disks without discrete tracks. Likewise, the "ambient" touch-down pressure at constant velocity was found to be higher for DTR disks than for smooth media. The hysteresis between touch-down and take-off velocity and touch-down and take-off ambient pressure was found to be larger for DTR media than for smooth media. Start/stop tests on discrete track media were performed to investigate the effect of grooves of discrete track media on the tribology of the head/disk interface. Source

Yoon Y.,Center for Magnetic Recording Research | Talke F.E.,Center for Magnetic Recording Research
Microsystem Technologies | Year: 2011

The contact deformation and wear characteristics of smooth and discrete track recording (DTR) media are investigated using nano-indentation and nano-scratch testing. Plastic deformation of the land areas between adjacent grooves was found to be substantially larger than in the smooth regions of the same disk. Reciprocating wear tests showed that wear was more severe for discrete track disks than for smooth disks. To improve the tribology of DTR media, planarization of discrete track disks appears to be necessary. © 2011 The Author(s). Source

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