Main Pole Research Articles

THE EFFECTS OF OPERATING CONDITIONS ON THE RELIABILITY OF THE COMPRESSOR MOTORS OF ELECTRIC DIRECT CURRENT

On the basis of the statistical data it is lead, research of influence of conditions of operation on reliability of engines of compressors. A principal cause of failure of engines is significant overheating windings of an anchor and the main poles owing to long overloads a current. One of ways of the decision of this problem is improvement of the equipment of protection.

Comparison of Micromagnetic and Point Probe Model in Magnetic Force Microscope Simulation

We developed a micromagnetic model of magnetic force microscopy (MFM) tip to compare it with the simple point probe model. We simulated the MFM signal to provide an understanding of the measurement of the field generated by the write head in perpendicular recording hard disk drives. When the magnetic pole density at the air-bearing surface of the head's main pole is increased from 0.2 T to 1 T, the MFM tip with vertical anisotropy shows a flower-state magnetization, while the tip with horizontal anisotropy has more complicated switching modes. It is found that the signal ratio of the two MFM tips with vertical/horizontal anisotropy does have a one-to-one correspondence to the average magnetic field in the tip; however, the signal ratio may change sign because of the magnetic moments' switching in the tip with vertical anisotropy. The result of micromagnetic simulation is quite similar to that of the point probe model, and has good agreement with experiments.

Automatic Calibration of Frequency Compensation System in Computer-Controlled Patch-Clamp Amplifier

Computer-controlled patch-clamp amplifier is a digitally controlled analog device used to record the cellular ion channel currents in electrophysiology research. The inherent bandwidth and performance of the headstage is limited by the stray capacitance and distributed capacitance across the feedback resistors. In order to effectively improve the performance of the headstage, the paper advanced a simplified automatic calibration method of frequency compensation system in resistor-feedback patch-clamp amplifier. The dynamic model of headstage was approximate as a two poles and one zero system in the transfer function by experience and test results, so the dynamic characteristics of the headstage were obtained employing least squares parameter estimation algorithm. Further more, the compensation parameter of high frequency booster can be estimated by the time constant of main pole of headstage. And automatic adjustment of the parameters in transient response correction stage was performed as a least squares fitting problem. The software routine running on the host computer conducted all operations of frequency compensation. Experimental results demonstrate that the simplified automatic calibration method can substantially extend the bandwidth and minimize step response error of headstage.

Micromagnetic Analysis of Switching Characteristics for Main Pole in Single-Pole-Type Head

A 3D micromagnetic model is established to analyze the dynamics of single-pole-type (SPT) heads, in which a main pole and a soft underlayer (SUL) are included. It is found that, in an SPT head whose write pole thickness L m and pole width W are 40 nm each, the throat height should be no greater than the pole tip width to avoid high remnant field at the static state. The influences of the head's parameters and the damping constant on switching time of SPT head are analyzed respectively. The crystalline anisotropy field of SUL is also proved to have great effect on the switching characteristics: a high anisotropy field along the cross-track direction could stabilize the magnetic moments in SUL and greatly shorten the switching time.

FEM Model Analysis of Single-Pole-Type Heads with Different Coil Structures

Pole-tip-driven structure, which is composed of a coil wounded at the main pole tip, is favorable for obtaining a sharp and strong head field as a single-pole-type head. Three kinds of pole-tip-driven-type heads with different yoke and coil structures are investigated in terms of magnetomotive force dependence of head field and effect of coil recession. Field calculation by finite-element method (FEM) showed that the three heads exhibited the same field sensitivity in spite of the difference in distribution of coil exciting field and magnetization of the main pole. In a lower range of magnetomotive force the heads showed different dependence of field sensitivity on the coil recession. However, there was not much difference in degradation of sensitivity in a region near the saturation of field. Thus, the importance of reducing coil recession was confirmed as reported earlier.

A Write Head Integrated With a Solid-Immersion-Lens System for Heat-Assisted Magnetic Recording

We have developed for heat-assisted magnetic recording a novel write head in which a magnetic writer and a near-field optical lens system are integrated. The single-pole type (SPT) write head is embedded in the hemispherical lens of a solid immersion lens (SIL) system, which has an effective NA of 1.44 at a wavelength of 405 nm. The SPT head, which has high magnetic efficiency and minimizes light scattering, consists of a main pole and vertical-turns type (VTT) coils. With an FWHM spot diameter of 130 nm and a main pole 2 mum wide, the head is estimated to be capable of small-spot writing

Return Field-Induced Partial Erasure in Perpendicular Recording Using Trailing-Edge Shielded Writers

Return field-induced partial erasure (RFPE) in trailing-edge shielded perpendicular writers has been studied, both by modeling and by experiments. For a given head-media combination, the return field underneath the trailing shield increases with increasing write current. Once exceeding a certain threshold, it will cause partial erasure of the bits that have just been written by the main pole. Recording performance, such as reverse overwrite, spectral signal-to-noise ratio, and bit-error rate are all found degraded at high write currents, due to RFPE. Design optimization of both head and media together is needed, in order to maximize the advantage of a trailing-edge shielded pole head and minimize the impact of RFPE

Write field measurements of a perpendicular head on a soft underlayer film

We demonstrate a technique to measure the field of a perpendicular head on a soft underlayer. We built a current-perpendicular-to-the-plane giant magnetoresistive sensor deposited on a soft underlayer and placed it on the write-read contact tester. Scanning a perpendicular head over the device with sub-nm resolution allowed us to map the field spatially and by changing the writer current, obtain saturation curves of both the main pole and the return pole.

Ultra-high magnetic moment films for write head

Novel magnetic materials with ultra-high magnetic moment are presented. The Fe/sub 70/Co/sub 30/ alloy is known to have the highest saturation magnetization of 2.45 T in nature. On the other hand, sputtered Fe/sub 70/Co/sub 30/:Pd and [Fe/sub 70/Co/sub 30//Pd]/sub n/ super-lattice films revealed higher saturation magnetization of 2.49 and 2.57 T at room temperature, respectively, while that of a Fe/sub 70/Co/sub 30/ single-layered film was 2.38 T. These values seemed to be acceptable of a main pole material of the write head in the hard-disk drive with an areal recording density above 160 Gbits/in/sup 2/. In addition, these films can be synthesized using a conventional sputtering apparatus as same as a Fe/sub 70/Co/sub 30/ films. Therefore, these films will promise a feasible way for the increase of an areal recording density without any additional technologies, such as a heat assisted recording, contact recording, or further development of the media.

Radar target identification using a likelihood ratio test and matching pursuit technique

On the basis of likelihood ratio test (LRT) theory, a new method for radar target identification with matching pursuits, including the estimation method for target scattering response and the extraction technique for the reference atom dictionary to characterise the target scattering, is introduced. When compared with the generalised LRT (GLRT) target identification method, there is a very important contribution in our method that the whole scattering waveform, not only a few main poles, is used to identify targets without any prior parameterisation model hypothesis. Furthermore, the identification to candidate targets can be performed in an almost aspect-independent manner over a full aspect angle in white Gaussian noise through a finite size reference atom dictionary. Simulation results using scattered responses synthesised from weighted sums of some exponentially damped sinusoids and calculated scattering signatures of three thin wires through a time-domain electric field integral equation are presented to contrast the performance of our method to the GLRT and the best LRT target identification method as a function of signal-to-noise ratio.

めっき法により作製したカスプコイル励磁型単磁極ヘッド

To enhance the write performance of a CF-SPT head, a smaller main pole of Co-Ni-Fe and a finer coil were fabricated by using the electrodeposition method. Fine coils with 2.5 μm pitch were obtained by the damascene process. The magnetic domain structure of the 15-μm-high and 20-μm-wide main poles could be controlled by changing their taper angles. A head with a favorable domain except at its tip exhibited stable write performance and no pole erasure. Thus, it was concluded that a control of the magnetic domain was necessary for write heads.

Newly developed wraparound-shielded head for perpendicular recording

We describe a fabrication process for a wraparound shield for perpendicular recording heads. We successfully made a wraparound shield on a main pole using this process. A wraparound-shielded head improved the resolution, and the byte error rate is lower compared to a single-pole head because the wraparound shield increased the gradient of the magnetic field from the main pole. Measurements in the cross-track direction showed that the wraparound shield improved the magnetic field profile at near the bottom of the profile.

The effect of write head structures on written transitions in perpendicular media

To increase the linear recording density in perpendicular media there are at least two issues, which should be addressed. The first is reduction of transition curvature, this can reduce the amplitude of the output signal and limit the linear recording density. A crescent-shaped main pole head has been proposed as one way to reduce transition-curvature. A second, related problem is how to increase the head-field gradient in the down-track direction. Higher head-field gradients allow sharper transitions to be written and delay the onset of percolation between written bits. One way to increase the head field gradient is to place a trailing shield behind the main pole. In this paper we make a detailed investigation of crescent-shaped main-pole heads and compare their recording performance with rectangular main-pole heads and heads with trailing shields.

Distribution of slanted write field for perpendicular recording heads with shielded pole

The write field distribution for a perpendicular writer was investigated using finite-element (FE) analysis. The slanted write fields due to shield pieces at the trailing edge and the leading edge of the pole tip, and the side shields are analyzed. The analysis shows that the use of the shielded pole leads to a change in the saturation levels in the main pole tip, affecting the write field distribution. The effects of the side shield and other design parameters on the write field in cross-track direction are discussed.

Write current optimization for single-pole and trailing-shield heads in perpendicular recording

Recording performance as a function of write current is studied for single-pole and trailing-shield heads. Optimal write current is not obvious from saturation curves. Media noise, jitter, and error rate give better guidance. For a single-pole head, there is an optimal write current, beyond which, the field strength may continue to increase, but field gradient degrades leading to higher noise. For trailing shield achieved by reverse-flying longitudinal heads, the field magnitude and gradient from the main pole continue to improve with increasing write current. However, the return pole erasure also increases. There is a critical current, above which, partial erasure from the return pole leads to excessive noise. Finite-element modeling of these two types of write poles has been performed to confirm and understand the experimental findings.

Nuevas tendencias en políticas de garantía de calidad en la educación superior

Higher education in Europe is undergoing a period of major transformations. Everywhere, emphasis is being placed on achieving the most crucial objectives of all : the construction of a common European Higher Education Area (EHEA). The EHEA constitutes a decisive step in the commercialization of higher education. In this context, quality assurance has a central role to play, being as it is at the intersection of current transformations. More in particular, the emergence of accreditation as the dominant objective of national policies for quality assurance in higher education can be understood as a crucial moment in the process of commercialization. The paper underlines this evolution by discussing recent evolutions in the domain quality assurance in higher education and stressing a number of potential risks and nega tive prospects. It offers a reflection organized around three main poles: quality assurance in higher education; the relationships with the process of commercialization and the actual use of the information that be collected through the many existing instruments for quality assurance. The paper strongly argues that a decisive shift has taken place since the late- 1990s that as replace formative purposes of quality assurance with summative ones

Micromagnetic-FEM models of a perpendicular writer and reader

We have developed a micromagnetic finite element method (micromagnetic-FEM) to analyze perpendicular magnetic recording (PMR) writers and readers. The head field reversal time is 0.55-0.76 ns including the 0.2-ns current rise, and it is dependent on the current amplitude. The main pole has a faster reversal time, but the yoke and media soft-magnetic underlayer (SUL) show a slower response. In the media recording layer, the trailing region shows a faster reversal due to the longitudinal head field component of the trailing write shield. After writing, the media state affects the remanent field behavior. Since the moving media changes the head-media coupling, the remanent field can be relieved with a long relaxation time within 10 ns. To suppress the remanent field, a good anisotropy control of the main pole and yoke is required. A TMR reader with a flat top shield shows less side-reading, especially when the physical track width is below 0.1 /spl mu/m. The PMR media plays a role in read width reduction over a wide range of physical track widths.

Simulations of perpendicular media for 400 Gb/in/sup 2/

Head and medium designs to support areal densities of 400 Gb/in/sup 2/ were investigated using micromagnetic modeling. The use of side shields allows the track pitch to be reduced, but only by about 10 nm. Reducing the main pole width also permits higher track densities, but the erase band width does not reduce significantly with the pole width reduction. In addition, the erase band width increases at higher linear densities and forms an increasing fraction of the total track width.

ＳＰＴ垂直ライトヘッドにおける反強磁性結合多層膜の膜構成最適化検討

Perpendicular magnetic recording using a single-pole-type (SPT) writer head and a double-layer perpendicular medium with a soft underlayer (SUL) has several advantages for high-density magnetic recording. It is therefore a promising candidate for a next-generation magnetic recording system. However, the pole-erase phenomenon, which is a signal reduction caused by a remanent head field from the main pole, prevents high-density recording. We investigated an SPT writer head with antiferromagnetic- (AFM-) coupled main pole to avoid the pole-erase phenomenon by using recently developed combined micromagnetics and finite-element method simulations. We demonstrated that the recording head field decreases monotonically with increasing number of AFM-coupled layers. On the other hand, residual field (pole-erase field) strength dramatically decreases to around half while applying an AFM-coupled bi-layer for the main pole. The pole-erase field is almost constant in the case of two or more layers. The optimum layer number of an AFM-coupled multilayer for the main pole is from two to four layers from the recording and pole-erase field point of view. We confirmed the same tendency by experimental observation of the pole-erase.

Controlling the written track width in perpendicular recording media

Recording simulations were used to determine the factors which influence the recorded track width in perpendicular media. Reducing the width of the main pole and adding side shields to the head are effective methods to write narrower tracks, whilst trailing shields can increase the SNR. Exchange coupling in the recording layer increases the track width, but erase bands are narrowed. However, the magnetisation of a pre-recorded track can influence the switching of grains at the edges of adjacent tracks if the exchange coupling strength is large.