Recording media research for future hard disk drives

Perpendicular magnetic recording (PMR) technology has recently been introduced in hard disk drives (HDDs) by almost all the HDD manufacturers. It is expected that because of PMR technology, the superparamagnetic limit can be circumvented until around 2012. At this stage, it is necessary to seek out alternatives to extend the current PMR technology, or to invent new alternatives to move beyond the PMR technology. There are several research opportunities becoming available, as we try to extend the competitive advantage of magnetic recording. This article is an attempt to provide a brief review of the research that has been carried out, interspersed with an analysis of possible new directions.     

A new lubrication equation for ultra-thin gas film in hard disk drives

To overcome the complicated and time-consuming difficulties of current models, a new lubrication equation based on boundary velocity slip model for solving the ultra-thin film gas lubrication in hard disk drives is proposed by adopting the nanoscale effect function, N _p. The present model is easy to calculate and applicable at nanoscale. The results of numerical calculations indicate that the present model produces a close approximation to that of the exact Boltzmann model.     

A new lubrication equation for ultra-thin gas film in hard disk drives

To overcome the complicated and time-consuming difficulties of current models, a new lubrication equation based on boundary velocity slip model for solving the ultra-thin film gas lubrication in hard disk drives is proposed by adopting the nanoscale effect function, Np. The present model is easy to calculate and applicable at nanoscale.The results of numerical calculations indicate that the present model produces a close approximation to that of the exact Boltzmann model.     

Design and analysis of vibration isolation systems for hard disk drives

Hard disk drives (HDD) are increasingly being used in mobile applications and consumer electronic devices in potentially harsh dynamic environments. In mission-critical applications such as in computers on board trains and military vehicles, the vibration experienced by the operating HDD can be very severe. An effective suspension system is necessary to isolate the HDD from the strong vibration transmitted from the ground, vehicle engine, etc. This paper gives details on how to design, test and evaluate vibration isolation systems for operating HDD subjected to very severe random vibrations based on military specifications MIL-STD-810E. One design is presented and evaluated based on well-defined criteria. Design principles on how to achieve the required degree of vibration isolation is described. A computer simulation model of an example design is formulated and correlated with experiments. It is shown that a low-cost, vibration isolation system can indeed be made that will allow an HDD to operate well when subjected to strong input vibration.     

硬盘驱动器巨磁电阻(GMR)磁头:从微米到纳米

近年来电脑硬盘存储密度的飞速增长(年增长100％)已超出摩尔定律的预言．这种惊人的高速增长中，最关键的因素是自旋阀纳米多层膜结构，即巨磁电阻(GMR)读传感器磁头的应用．事实上，巨磁电阻磁头读传感器(reader sensor)已经实现由微电子器件向纳米电子器件转化，并且形成大规模产业．这一过程包含了自旋电子学、材料科学、微电子工程学、化学、微机械力学和工程学等诸学科和相关微加工技术综合性挑战极限，进入纳米科技领域实质性进步．     

On the absence of charge symmetry in electrostatic interaction between charged drops and hard particles

It is shown that the analytical expressions for the energy and force of electrostatic interaction between charged conducting particles (drops), a point charge, and a finite-size particle, as well as between a particle (a drop or a point charge) and a conducting plane, are asymmetric with respect to the sign of one of the charges. This is because the polarization interaction is always attractive irrespective of the signs of interacting particles. The absence of this symmetry leads to the self-constriction of charged aerodispersed systems containing a condensed phase, for example, plasma or liquid-droplet systems.     

The mean spherical model for charged hard spheres

The reduced mean electrostatic potential v(r) and the radial distribution functions gij(r) for a system of charged hard spheres of equal diameter are calculated from the solution of the mean spherical model equation given by Waisman and Lebowitz. An analytical solution is given for v(r) and the gij(r) are shown to be the sum of the Percus-Yevick uncharged hard-sphere distribution function and an electrostatic term. The correct qualitative behaviour of the mean potential is predicted at high concentrations but the radial distribution functions are only accurate for low valency electrolytes at high concentrations.     

Equations of state for the hard disk fluids

By using the published accurate new virial coefficients B₁₁～B₁₄ for the hard disk fluids [C. Zhang and B.M. Pettitt, Mol. Phys., 2014, 112, 1427], we here propose a new updated version of Tian-Gui-Mulero equation of state [J.X. Tian, Y.X. Gui and A. Mulero, Phys. Chem. Chem. Phys., 2010, 12, 13597]. Compared with other proposals, the new version stands strongly to be the only which can reproduce the known virial coefficients B₂～B₁₃ at the same time that can describe the relation of the compressibility factor versus the packing fraction for the hard disk fluids with high accuracy.     

Simple approach for charge renormalization in highly charged macroions

We revisit the notion of renormalized charge, which is a concept of central importance in the field of highly charged colloidal or polyelectrolyte solutions. Working at the level of a linear Debye-Hückel-like theory only, we propose a versatile method to predict the saturated amount of charge renormalization, which is, however, a nonlinear effect arising at strong electrostatic coupling. The results are successfully tested against nonlinear Poisson-Boltzmann theory for polyions of various shapes (planar, cylindrical, and spherical), both in the infinite dilution limit or in confined geometry, with or without added electrolyte. Our approach, accurate for monovalent microions in solvents such as water, is finally confronted against experimental results on charged colloids and B-DNA solutions.     

Variational charge renormalization in charged systems

We apply general variational techniques to the problem of the counterion distribution around highly charged objects where strong condensation of counterions takes place. Within a field-theoretic formulation using a fluctuating electrostatic potential, the concept of surface-charge renormalization is recovered within a simple one-parameter variational procedure. As a test, we reproduce the Poisson-Boltzmann surface potential for a single-charged planar surface both in the weak-charge and strong-charge regime. We then apply our techniques to non-planar geometries where closed-form solutions of the non-linear Poisson-Boltzmann equation are not available. In the cylindrical case, the Manning charge renormalization result is obtained in the limit of vanishing salt concentration. However, for intermediate salt concentrations a slow crossover to the non-charged-renormalized regime (at high salt) is found with a quasi-power-law behavior which helps to understand conflicting experimental and theoretical results for the electrostatic persistence length of polyelectrolytes. In the spherical geometry charge renormalization is only found at intermediate salt concentrations, in agreement with previous numerical results.Received: 16 December 2002, Published online: 22 July 2003PACS: 82.70.-y Disperse systems; complex fluids - 61.20.Ja Computer simulation of liquid structure - 61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc.     

磁记录硬盘介质研究进展

硬盘磁记录介质是磁性材料应用的一个重要方面,目前在信息存储领域占有重要的地位.文章概述了磁记录硬盘介质的发展过程以及研究和开发的状况,并对硬盘未来的发展前景作了分析.     

磁记录硬盘介质研究进展

硬盘磁记录介质足磁性材料应用的一个重要方面,目前在信息存储领域占有重要的地位.文章概述了磁记录硬盘介质的发展过程以及研究和开发的状况,并对硬盘未来的发展前景作了分析.     

磁盘润滑膜全氟聚醚的分子动力学模拟研究

纳米润滑膜全氟聚醚(perfluoropolyether，简称PFPE)在固体表面的结构和迁移特性对于计 算机磁盘磁头驱动系统的可靠性具有重要的作用. 采用基于粗粒珠簧模型的分子动力学模拟 方法，考察了不同壁面和端基极性对于PFPE膜静态特性（如分子构型、单体密度分布、端基 密度分布）以及动态特性（如自扩散系数）的影响. 静态特性的模拟结果表明，非极性PFPE 膜在壁面附近具有单层厚度为一个单体直径的层状结构，而极性PFPE膜则具有复杂的层状结 构. 动态特性的模拟结果表明，PFPE膜的扩散能力因壁面作用而增强并因端基极性作用而减 弱. 关键词： 全氟聚醚膜 分子动力学模拟 薄膜润滑 固液界面结构     

A miniature ultransonic pump using a bending disk transducer and a gap

It is known that if a pipe end is faced at a vibrating surface in liquid with a small gap, liquid is suctioned into the pipe. As a miniature configuration, we introduce a bending disk transducer 30 mm in diameter using a ring-shaped PZT element. The disk vibrator is worked at the fundamental resonance frequency of 19 kHz of the bending mode. To optimize the pipe geometry, we experimentally investigated the effect of the outer diameter on the pump performance. As a result, the outer/inner diameter ratio of 3:2 is optimum for the gap smaller than 20 microm. We achieved the maximum pump pressure of 14.8 kPa and the maximum flow rate of 10 ml/min. using the prototype pump.     

Glass transition line for the system of charged hard spheres

We locate the glass transition line of the charged-hard-sphere system in the density-temperature plane, using a mean-field hypernetted chain approximation within the replica-symmetry-breaking scenario [S. Franz and G. Parisi, Phys. Rev. Lett. 79 (1997) 2486. [11]]. Our results demonstrate a dominant role of the steric factor and explain the ineffectiveness of purely Coulombic interactions in driving phase transitions.     

Study of attempt frequency in Sharrock's formula for perpendicular recording hard disk media

Change of the attempt frequency f_o in Sharrock's formula as functions of magnetostatic and inter-grain exchange couplings has been investigated using micromagnetic simulation. It was found that f_o increases monotonically with increasing the magnetostatic coupling, whose mechanism is not understood yet. It was also found that f_o decreases initially with increasing the inter-grain exchange coupling, below a critical value and increases above it. The initial decrease is likely due to that the exchange coupling depresses the effect of the magnetostatic coupling, because the effective fields from the neighboring grains are competing with each other. The increase of f_o above the critical value is deeply related to the increase of the thermal activation volume V.     

波带板法检测非球面技术

总结了在波带板干涉技术检测非球面方面最近的发展和应用，比较了不同方法的优缺点。叙述了用一块改进型波带板检测非球面的原理和方法。还分析了波带板的安装与测量精度的关系。针对干涉条纹在周边弯曲的现象，对波带板的设计进行了改进。最后给出了实验结果。     

Hydrated zirconia nanoparticles as media for electrical charge accumulation

Journal of Nanoparticle Research - The series of LaF3 nanoparticles with closed pores filled with water H2O and heavy water D2O are synthesized by the hydrothermal treatment in autoclave at...     

Electrostatic field and charge distribution in small charged dielectric droplets

The charge distribution in small dielectric droplets is calculated on the basis of continuum medium approximation. There are considered charged liquid spherical droplets of methanol in the range of nanometer sizes. The problem is solved by the following way. We find the free energy of some ion in dielectric droplet, which is a function of distribution of other ions in the droplet. The probability of location of the ion in some element of volume in the droplet is a function of its free energy in this element of volume. The same approach can be applied to other ions in the droplet. The obtained charge distribution differs considerably from the surface distribution. The curve of the charge distribution in the droplet as a function of radius has maximum near the surface. Relative concentration of charges in the vicinity of the center of the droplet does not equal to zero, and it is the higher, the less is the total charge of the droplet. According to the estimates the model is applicable if the droplet radius is larger than 10 nm.