Anomalous wavelength response of a thin film head from double-layer perpendicular media

The readback signal of a thin film head from a double-layer perpendicular medium shows enhanced undulations in the amplitude versus density plot. These undulations are an order of magnitude greater than that observed in the longitudinal recording. In addition, the null response usually occurs at a wavelength much longer than the gap length. This anomalous wavelength response is attributed to the interaction between the head and the underlayer. Three models with different degrees of head-underlayer interaction are used to analyze this phenomenon. Experimental data are presented and compared with these models. The effect of the pole length, gap length, medium thickness, and head-to-medium spacing on the wavelength response is also discussed.     

Pulse distortion in transitions recorded with thin film pole tips

The transitions recorded on particulate, longitudinal media by a thin film ring head can exhibit a distortion at high write currents that adds an oscillatory structure to the density response and also degrades the amplitude at high density. The main data transition is recorded at the trailing edge of the gap, while the distortion is a second pulse written at the edges of the data track by the trailing edge of the trailing pole tip and at the expense of the transition recorded by the gap. This produces two pulses of opposite polarity with a constant peak-to-peak amplitude, separated by a distance equal to the thickness of the trailing pole tip and with the distortion appearing as a spurious pulse ahead of the data pulse.     

A graded magnetization single pole head for perpendicular recording

The magnetic field of a graded magnetization single pole head in the presence of a highly permeable magnetic underlayer is analyzed. Vertical field amplitudes and gradients in the region close to the trailing edge of the pole are shown to be higher than those produced by a conventional single pole. For a perpendicularly magnetized medium, output spectral response functions, roll-off curves and peak shift computations indicate improved replay performance. The exact theoretical solution is obtained in the form of an infinite series using Fourier analysis but it is shown that the leading term alone can lead to a simple and accurate approximation. New theoretical results are also presented for a constant potential pole, including a simple approximation to the field and explicit exact formulae for certain output calculations     

Improved method of calculating the Fourier coefficients of amagnetic pole head

An improved method of calculating the Fourier coefficients for a single unshielded magnetic pole head is presented. The method is based on the knowledge of the exact Fourier coefficients for a magnetic ring head     

Effect of pole-tip size on perpendicular recording head remanence

To aid understanding the physical mechanisms responsible for the perpendicular write head remanent field and thereby improve the write head design, we studied the remanence of single-pole perpendicular recording heads with trailing shield by using a contact scanning recording tester. We used two different pole-tip size heads in the study. We found that the remanence areas of the heads tested usually locate at the trailing edge corners of the pole tip. We also found that the remanence areas of both types of heads are also the head field easy-rising areas when the heads are driven by low write currents. Additionally, the current level that leads to remanence is the same for both types of heads. However, the remanence of the small pole-tip heads can be demagnetized by a much lower amplitude reverse current than that of the large pole-tip heads.     

Efficiency and inductance analysis of a three-region thin-film head

Expressions for the efficiency and inductance of a thin-film magnetic head are derived using an extended transmission-line model. This extension was performed by applying the Paton-Jones unidimensional model to an actual head geometry, with three regions in the longitudinal cross section: a pole tip region, a coil region, and a back protection region. The computer analysis of the efficiency and inductance is used to predict geometry optimization of the head.     

The dependence of recording characteristics of thin metal tapes on their magnetic properties and on the replay head

A theory is derived to explain the recording properties of thin metal tapes in terms of their magnetic properties and in terms of the losses within the replay head. The tape losses are considered as being due to self-demagnetization and head losses resulting from gap and separation effects. The reproduction of isolated pulses is first considered and then modified to the condition of pulse crowding. A comparison of theory with experiment shows that the theory is sufficient in its prediction of head losses but has some limitations in its prediction of tape losses at high packing densities.     

Application of thin film head technology to a high performance head/track disk file

Processing technologies and performance parameters of thin film recording heads used in a 6.7Mbyte disk memory are presented. Photolithographic, vacuum deposition, and ceramic substrate fabrication procedures are described for a single turn, multi-track head assembly. Interlayer diffusion and thermal heating are described. Data relating spacing loss, bit density, gap geometry, and write currents to signal amplitude and timing are given for NiCo media. Special cables and integrated write/read IC's are described.     

A least squares method for fitting head fields by parametricequations

Models of magnetic recording systems generally require the field of the record head to be calculated. In the interests of speed a simple, but accurate, analytic expression is desirable. In this paper the method of minimization of squared residuals is used to obtain parameters defining a parametric approximation to the head field. As an example parameters are obtained which give best fits to finite pole tip head fields produced by conformal mapping. It is found that a good set of parameters is obtained by separately characterizing the infinite pole length head field and correction terms due to the outer pole edges evaluated at the medium surface. The same method could be used to fit measured data or fields obtained using numerical models     

斯特林型脉冲管制冷机中压缩机与冷指耦合实验研究

从理论上分析了质量流和压力波对脉冲管制冷机中冷指和压缩机耦合的影响, 针对1台6 W/95 K斯特林型脉冲管制冷机行了具体研究.实验分析表明:只有当线性压缩机能够提供脉冲管冷指所需的压力波动和质量流量时,整机才可能取得较好的性能;运行频率和整机的输入功率对压缩机效率的影响都小于2%.     

A new thin film scanning head for magnetic printing

Magnetic printers are subject to serious limitations, due either to the requirement to move the printing head, or to use multiple heads. The purpose of this paper is to describe the principle of a new head which allows a microline to be recorded by scanning a stress in a head which has magnetostrictive pole pieces. Stress characteristics are described and the changes in the magnetic behaviour of two suitable stress sensitive magnetic alloys are given. Finally, the head limitations are discussed.     

A new W-shaped single-pole head and a high density flexible disk perpendicular magnetic recording system

A new single-pole head with no auxiliary pole was developed for perpendicular magnetic recording. The head is called WSP head (W-shaped Single Pole head) because the head has a W-shaped side core which contributes to increase the recording and reproducing sensitivitiy. The head field of the new head has the same distribusion as that of an auxiliary pole head[1]. The recording and reproducing sensitivity of the head is equal to or higher than that of a ring-type video head. The head eliminates mechanical problems which prevent its application in perpendicular magnetic recording because we can locate the head on one side of the recording medium. As a possible application of the WSP head, a 3 1/2-inch flexible disk recording system was constructed. A linear recording density of the flexible disk system was 65.5 kbits/inch. This density is equivalent to 8 times that of the existing high-density 3 1/2-inch micro-floppy and 11 times that of a 5 1/4-inch floppy disk. In termes of information storage, this density gives a 4 megabyte unformated capacity on one side of a 3 1/2-inch flexible disk. The overwrite signal-to-noise ratio was greater than 30 dB and the peakshift displacement was less than 10 % at the linear dinsity of 65.5 kbits/inch.     

Design and performance of a recessed thin film inductive transducer

An improved inductive transducer is achieved by placing the coil and the majority of the transducer body into a recessed alumina basecoat. Process advantages of a recessed over planar structure includes lower top pole topography, improved pole trim capability, and improved top pole composition uniformity. Coil and photoresist processing in a recessed cavity allows for multiple layers with lower resistance without increasing transducer Permalloy path length. Recessed trimmed design performance has increased efficiency with higher amplitude and a narrower pulse width along with improved overwrite compared to planar untrimmed transducers. The recessed basecoat design is explained, and compared to planar transducers using modeling and performance results     

移动硬盘磁头驱动臂的模态分析与脉冲响应

磁头驱动臂组件是硬盘驱动器内重要的机械部件,其冲击载荷下的动态响应是影响硬盘驱动器抗振性能好坏的主要指标。本文以2.5英寸移动硬盘驱动器组件为研究对象,在考虑枢轴轴承刚度影响的基础上,建立了驱动臂组件的三维有限元模型,分析了其各阶振动模态,并讨论了脉冲波形、脉冲幅值、脉冲宽度对磁头驱动臂组件动态响应的影响。     

The reading characteristics of a finite length pole piece recording head

The frequency response of a finite-length pole piece recording head is calculated numerically for various gap-to-pole-length ratios as well as for differing head-to-medium separations for an idealized sinusoidal magnetization distribution by application of the Cooley-Tukey fast Fourier transform.     

Perpendicular stand-still recording in Co-Cr films

Some features of perpendicular recording were investigated by means of stand-still recording experiments. For this purpose several radio frequency (RF)-sputtered Co-Cr layers of two different compositions were used as media while a Permalloy single pole (SP) head was used as a write transducer. A magnetoresistive transducer (MRT) was utilized to read the recorded pattern. Further, an analytical model was developed enabling the magnetization induced by the head field in the recording medium to be calculated. Both calculations and experimental results show a sharpening of the transition, due to the demagnetizing field. For a good approximation it is sufficient to consider only the vertical head field component and vertical magnetization in the recording medium. This is a consequence of the well-developed perpendicular anisotropy and negligible in-plane remanence of the Co-Cr layers. In addition the read-out signal is completely determined by the magnetic surface charges. The remanent magnetization in the recording medium and therefore the read-out amplitude is limited by demagnetization and consequently determined by the coercivity of the Co-Cr layer. The medium noise of a dc-erased medium indicates magnetic structures of much larger dimensions than the size of the individual crystallites. This noise appears to be dependent on the saturation magnetization of the Co-Cr medium. Activation of the single pole head by a homogeneous field results in a nonlinear behavior, caused by head saturation effects. This is supported by simple one-dimensional calculations of the head field.     

Wavelength response of perpendicular magnetic recording

From the measurements of the surface field of a recording medium, it was obtained that an almost ideal step change distribution of magnetization is formed in perpendicular recording for digital signals. The fact represents that the upper limit of usable recording density is determined only by the resolution of a reproducing head. Therefore, the reproduction by a perpendicular head was successfully analyzed by using the reciprocity theorem. By introducing thickness loss of main pole of the head, the satisfactory coincidence was obtained between the calculated and the measured results in the wavelength response even at the densities of more than 150 kMRPI. In reproducing process, the magnetic interaction between the main pole and the medium acts so as to decrease the effective spacing between them.     

Dependence of reproducing gap null on head geometry

The spatial frequency response of reproduce heads with infinite depth, but finite pole length, is determined to very good accuracy by superposition of conformal map solutions for simpler geometries. This approach yields closed form approximations of the frequency response which are accurate to better than 7% for any head length-to-gap length ratio and any spatial frequency. In particular, the effect of this ratio on the location of the first gap null in the frequency response spectrum is explored for narrow pole length heads. The results lead to design considerations for extending the useful frequency range of thin film reproduce heads.     

A technique for measuring pole tip saturation of low inductance heads

Increasing the coercive force of a magnetic recording medium normally improves high density digital performance. However, in rigid disk systems, the head is not in intimate contact with the disk. In addition, the ferrites employed as head materials have much lower saturation magnetization than the metals normally used in other types of heads. Under these conditions, the head field may be inadequate to fully saturate recording media of higher than normal coercive force. In the development of the latest disk products, increasing the coercive force has not improved performance but has increased overwrite modulation. This situation has not been improved by increasing write current amplitude. Pole tip and core saturation of the record head has been suspected as the cause of these observations. This paper describes a method of characterizing saturation effects in low inductance heads such as those used with rigid disks. Evidence of the deterioration of performance due to pole tip and core saturation is shown from isolated pulse measurements on a rigid disk with NiZn and MnZn ferrite heads.     

Monte Carlo simulation of thin film head read-write performance

Read-write simulations of thin-film head longitudinal recording performance with thin-film disks are described. Acceptable electrical performance of thin-film heads depends on tight control of numerous parameters, and Monte Carlo simulation is used to quantify read-write sensitivity to head variations and to identify the critical parameters. A population of similar heads is assumed, and ten head parameters are subjected to random variations. The resultant electrical performance is dominated by head-disk spacing, with throat height, gap length, trackwidth, and pole thickness following in order of importance. Reasonable variations in coil resistance insulation thickness, yoke thickness, magnetic permeability, or inductance show relatively little influence on recording performance