Analysis of Rarefied Effects of a Nano-scale Magnetic Head/Disk

When the decrease in the space between magnetic head and disk arrived at 10 nm or less, which is much lower than the mean free path of gas molecules, the gas flow presents distinctive features against the macro features because of the rarefied effects. The modified Reynolds equation considering rarefied gas effect is used to calculate the rarefied region of a negative pressure magnetic head working in the distance of 10 nm. Inverse Knudsen number was adopted to calculating the ratio of the rarefied area. According to the numerical resuks, discussions and analyses are then presented to reveal the rarefied effect on the working performances of a magnetic head. The results show that the magnetic head works in the slip-flow and transition regions and moves to the transition region with the increase in velocity. Furthermore, the maximum rarefied effects occur at the side edges where the flying height is thinner and pressure is lower, rather than in the minimum flying height on the rear. The results also show that with considering the rarefied effects, the load-carrying capacity of the magnetic head and the maximum pressure decrease significantly, but the minimum pressure slightly changes.

STABILITY ANALYSIS OF COUPLED SYSTEM OF MAGNETIC HEAD AND ULTRA-THIN GAS FILM

This paper presents a pressure perturbation equation for the ultra-thin gas film lubrication of magnetic head-disk based on a generalized gas lubrication equation applicable to arbitrary Knudsen number. The gas film pressure of Air Bearing Slider (ABS) was obtained by using the operator-splitting and finite element method. The pressure perturbation equation was solved by the finite element method with unstructured triangle grids to calculate the stiffness and damping coefficients of the gas film. Modal analysis of coupled system of magnetic head and gas film was carried out to obtain natural frequencies, damping rates and mode shapes of the magnetic head vibrations. Vibration stability of Ω-type magnetic head was predicted in this work. Numerical results indicate that the natural frequencies of the coupled system increases as the gas film thickness decreases, and the natural frequencies and damping rate of the coupled vibration modes of heave and pitch motions are much lower than those of uncoupled modes. And it is concluded that the stability of magnetic head is slightly worsened when the disk rotation speed increases.

SUB-NANOMETER POLISHING OF MAGNETIC RIGID DISK HEADS TO AVOID POLE TIP RECESSION

For the purpose of solving the problem that too large pole tip recession （PTR） is produced in magnetic rigid disk heads by mechanical polishing, a chemical mechanical nano-grinding experiment is performed by using a float-piece polisher with a tin plate to achieve a more plane and smoother surface. A basal solution, addition agents and a range of pH value are suitably selected to find a kind of slurry, with which the PTR can be controlled on sub-nanometer scale and the giant magnetic resistance （GMR） corrosion and electrostatic damage （ESD） can be avoided. Moreover, the cause that TiC protrudes from the substrate surface of the heads is studied. The appropriate shape and size of diamond abrasive are selected according to the chemical activation of A1203 and TiC in the same slurry. In this way, the chemical and mechanical interactions are optimized and the optimal surface that has small PTR and TiC asperity is achieved. Ultimatily, the chemical mechanical nano-grinding in combination with mechanical nano-grinding is adopted. Sub-nanometer PTR is achieved and the TiC asperity is eliminated by the chemical mechanical nano-grinding with large size ofmonocrystalline followed by mechanical nano-grinding with smalle polycrystalline diamonds.

Analysis on Dynamic Characteristics in Time Domain of Slider with Ultra Thin Spacing

With increasing recording density in computer hard disks,the flying height of the magnetic head becomes 10 nm or less.The numerical method of the control equations needs to be optimized consistently with the decrease of the flying height.The iterative process is usually divergent with traditional methods which cannot ensure the accuracy of the analysis results and the stability of numerical calculations.Firstly,a new scheme is presented to solve the ultra-thin lubricating control equations in this paper.The equilibrium equation is obtained by taking the Couette flow terms and time term as dominating terms in iterative process.Moreover,the weighting flow factor is introduced for the abrupt change of film thickness in order to reduce calculated deviation.Secondly,the rules for variation of flying pose of the magnetic head with time are obtained by the time domain analysis.The results show that the magnetic head can recover to the equilibrium position after being slightly influenced by outside disturbance.And the dynamic lubrication properties of the head suffer heavily from the vibrations in the height direction and fluctuation in the pitch direction.Finally,the analysis of the sine roughness-passing capacity of the head indicates that the head can surpass small sine waves and the equilibrium position can be retrieved after a period of decaying oscillation.The proposed research ensures the accuracy and stability of the numerical calculation of the control equations,and the dynamic characteristics and flying stability of a magnetic head is studied systematically.It can also be the theoretical basis for the analysis of the flight characteristics of the slider.

The Laser Doppler Shift Method for Measuring Slider Flying Characteristics

The basic principle ,optical system and measured results of the laser Doppler shift method for measuring slider flying characteristics are presented in this paper.