Inductive Head Research Articles

Thermal pole tip protrusion finite element analysis of thin film inductive recording heads

In recent low flying height hard disk drives, the head write current causes thermal protrusion of the pole tip region that results in head–disk contact. Finite element analysis is performed in this work to study the temperature and displacement fields in heads during writing. Three-dimensional steady-state thermal-structural analysis of a head in air and over a disk is presented. Complex head geometry is modeled. Velocity slip and temperature jump boundary conditions are used in formulating heat transfer through the air bearing. Moreover, transient analysis of head thermal protrusion is presented. Step direct current is applied. Snapshots of the temperature field as well as temperature and displacement time functions of several locations in the head are exhibited. It is found that head protrusion first occurs at the pole tip, then spreads to the trailing end of the slider. For the head–disk interface studied, it takes 0.6 ms for the head to come in contact with the disk after writing starts.

The dual spin valve head for high density recording

A dual spin valve head with synthetic antiferromagnetic pinned layers, DSSV, consists of a reader and a writer. The key fundamental concept of the magnetic materials for the reader and the writer of the DSSV will be discussed in this paper. The reader consists of a sensor stripe, a pair of hard magnetic bias films for the purpose of stabilization, and a pair of current leads. The reader has a high sensor sensitivity because it allows a longer coherent spin dependent electron mean free path that enhances the giant magnetoresistance change. The sensor is a symmetrical multilayer film structure that was optimized to have a high GMR ratio. The writer is a conventional inductive head with high magnetic moment poles consisting a thin layer of laminated high moment FeRhN film material The multilayer film sturcture of the DSSV sensor, its magnetic properties, and the head performance will be discussed in detail. The possible future development will also be discussed.

Microstructures of FeTaN films in the neck region of magnetic recording heads

We found that the columns at the neck region of a magnetic recording inductive head slider composed of FeTaN and NiFe are tilted from the surface normal when the pole materials are sputtered at a low substrate bias power. The electron diffraction patterns show that [110] texture has not strongly developed in the FeTaN film. We have not observed noticeable voids throughout the film on the slider, which suggests the absence of microshape anisotropy. This observation is consistent with our previous study of FeTaN blanket films. We confirmed lattice distortion in the FeTaN due to Ta and N incorporation into a Fe matrix. No significant difference in microstructure between the film on the head slider and the blanket film is found. Based on all the information we have gathered, such as X-ray spectra, pole figures, and high-resolution electron micrographs, we established the crystallographic relationship between [110] orientation, columnar direction, and incident atomic flux in the case of oblique-incident deposition of FeTaN films.

High-density reproduction characteristics with MR head for rotary drum in helical-scan tape system

A magneto-resistive (MR) head for a rotary drum in a helical-scan tape system has been developed to realize a high-capacity tape storage system with a high data transfer rate that uses a small cassette. Also, various experimental ME (Metal Evaporated) tapes whose magnetic layer thickness is 0.1 /spl mu/m or less (thin-magnetic-layer ME tapes) for the MR head has been fabricated. Reproduction characteristics of the MR head with the ME tapes was evaluated. The output voltage of the MR head was 20 times that of a conventional inductive head. An areal recording density of 1.2 Gbit/inch/sup 2/ was found to be possible combining the MR head with the thin-magnetic-layer ME tapes whose magnetic layer thickness was 0.09 /spl mu/m.

Comparisons of standard and modified perpendicular magnetic recording disks with ring head writing

To overcome the superparamagnetic effect in longitudinal magnetic recording (LMR) technology, the combination of perpendicular magnetic recording (PMR) media by writing with an inductive ring head has been suggested as one of the candidates to overwhelm the thermal fluctuation of the recorded magnetization. This has specially attracted attention on its practical application to hard disk drives (HDD), because the conventional LMR head can apply to new PMR disks. In this research, the four types of standard single and double, and modified thin single- and pseudo-double-layered PMR disks are fabricated and evaluated in terms of crystallographic and magnetic properties. Read/write performances of the modified disks by a merged giant magneto resistive (GMR) head show superiority in signal-to-noise ratio (SNR) to those of the standard disks.

Magnetoresistive read heads for high-density data applications

We present experimental results such as channel response, signal-to-noise ratio, bit-error rate, and wear of anisotropic magnetoresistive (AMR) helical scan read heads compared to respective values of inductive ferrite read heads. The presented measurements indicate the advantages of the AMR head.

Magnetic materials and structures for thin-film recording media (invited)

There have been three distinct stages in the development of magnetic materials and processes for thin-film media. The first era focused on designs for use with inductive heads. Vacuum sputter deposition techniques were developed to achieve high Hc, with high Ms materials epitaxially grown on Cr underlayers. The second phase of thin-film media development demanded media optimized for the use with MR heads. Noise reduction through the decoupling of grains by chemical segregation of Cr at the grain boundaries proved effective. The introduction of giant magnetoresistance heads required low noise and high Hc but added the necessity of the reduction in the average grain size and grain size distribution width. The next and perhaps final phase of thin-film media development will be focused on the minimization of the magnetization thermal decay by the use of materials and designs that produce high KuV/kBT ratios.

Approximating the magnetic recording step response using a Voigt function

A simple, closed-form expression for the step response or pulse shape of a magnetic recording channel is described. The step responses of inductive and magnetoresistive heads with thin-film media are shown to be well approximated by a Voigt function (the convolution of a Lorentzian and a Gaussian function). For convenience, an accurate approximation to the Voigt function (the linear superposition of a Lorentzian and a Gaussian function with appropriate weighting) was fit to the step responses using one adjustable parameter. The improved accuracy of this approximation to the step response has a strong impact on channel performance analysis and modeling.

Flexible media — recent developments from the tribology point of view

With the increase in the recording density of hard disk systems, the demand on the increase in the data recording capacity of tape drive systems as back-up systems is increasing. One of the advantages of the tape drive systems is high volumetric recording density, which is obtained by high areal recording density and thin tapes. The areal recording density can be increased by introducing high performance tapes, such as metal evaporated tapes, with superior magnetic characteristics and smooth magnetic surface to reduce the spacing loss. However, a smoother surface often produces a higher friction coefficient, which could cause tape damage by rotary heads and unstable tape runnability in the tape drives. Adoption of MR heads to tape drive systems is also effective in increasing the areal recording density. However, the wear allowance of the MR heads (shield type) is much smaller than that of the inductive heads. Thinner tapes show lower mechanical stiffness in general, which could cause damage to tape edges easily during tape transportation. In the second or later generation of tape drive systems, a thinner tape is often introduced. These thinner tapes should also have the interchangeability of the original thickness tape. New materials for a base film, such as PEN (polyethylene naphthalate) or aramid in which the elastic moduli are larger than those of PET, are required for thinner tapes. It was found that these side effects by the increase in the volumetric recording density can be improved by tribology. The tribological improvements from the drive design side is very important, as well as from the tape design side.

Size effect on magneto-impedance in layered films

The analysis of magneto-impedance (MI) in a sandwich film having an inner conductive lead and two soft ferromagnetic layers is concerned with the role of the film dimensions in determining the MI ratio. The equation for the AC magnetic field distribution in the sandwich is solved making the assumption of a weak skin-effect and a large transverse permeability of the magnetic layers. The flux leakage through the conductive layer results in a considerable drop in MI ratio if the film width is less than a certain critical value depending on the transverse permeability and the layer thickness. This process is similar to that known in inductive recording head, for example, in contributing to head efficiency.

Demonstration of a magnetic angular position sensor with ultra-high resolution and accuracy

In this study, a magnetic angular position sensor with 160,000 pulses/rev and 0.4 in. of the accuracy is obtained using a longitudinal disk, magnetoresistive (MR) sensors and a new method of formatting magnetic poles on the disk. The magnetic poles are formatted by a thin film inductive head with 6 μm of trackwidth and 0.7 μm gap length. Angular position signals are reproduced by two MR sensors which are commercial MR heads with 4 μm trackwidth and 0.6 μm gap length maintained in phase quadrature with each other. In order to format equally all magnetic poles on the disk, the central frequency of the writing signal must be equal to the central frequency of the speed of disk and the steadiness of the disk speed and writing frequency must be as high as possible.

Magnetic properties, microstructures, and corrosion resistance of high-saturation FeMoN and FeRhN films for recording heads

We have investigated high-saturation FeMoN and FeRhN films, deposited by radio frequency-diode reactive sputtering on alumina-TiC substrates, for inductive head applications. A minimum coercivity of /spl sim/1.2 Oe is obtained in (Fe/sub 97.8/Mo/sub 2.2/)N films at a N/sub 2//Ar flow ratio of /spl sim/6.2%. A minimum coercivity of /spl sim/1.6 Oe is obtained in (Fe/sub 96.9/Rh/sub 3.1/)N films at a N/sub 2//Ar flow ratio of /spl sim/4.6%. The films mainly consist of /spl alpha/-Fe phase and /spl gamma/'-Fe/sub 4/N phase; The magnetic properties of these films are stable under easy axis field annealing up to 350/spl deg/C. Addition of Rh or Mo to FeN has resulted in a significant improvement in corrosion resistance over that of FeN. The localized corrosion resistance of FeRhN and FeMoN can be comparable to that of Permalloy. In contrast, their intrinsic corrosion resistance is inferior to that of Permalloy, but it can be adjusted and controlled by pH level.

Magnetic analysis of contact head/tape spacing

A new magnetic analysis method is used to determine the mean magnetic spacing of a contact head/tape interface. The initial part of the curve of readback signal amplitude versus recording current is measured at a low recording density and is fitted by using theoretical approximations to obtain the head/tape spacing. A tape looper test stand, inductive heads, and various high-density metal particle tapes are used in the recording measurements. The mean head/tape spacing obtained from magnetic analysis agrees well with the results from numerical analysis of mechanical measurements.

More than 1 Gb/in/sup 2/ recording on obliquely oriented thin film tape

We discuss the possibility of attaining more than 1 Gb/in/sup 2/ recording in helical scanning tape storage system based on obliquely oriented metal evaporated tapes. A demonstration of 1 Gb/in/sup 2/ recording using an inductive MIG type head is described. Other experimental results show that the obliquely oriented Co-O tapes are endowed with recording resolution potential beyond several Gb/in/sup 2/, but playback signal-to-noise challenges still remain. Applying more sensitive magneto-resistive heads in the helical scanning tape system requires significant innovation in the system to overcome crucial issues of contact recording as well as re-optimization of the magnetic properties of the tape.

Magnetic thin films in recording technology

This paper is a review of recent progress in magnetic thin films for use in recording media and heads. Emphasis is on work that has been carried out at IBM. Topics covered include thin-film media for high-density recording, laminated soft-magnetic films for controlling domains and extending the frequency range of inductive heads, exchange-biasing of magnetoresistive sensors, and magnetic multilayer structures.

Track profile of MR head and its performance in a helical scan tape system

The MR head is being studied for use in helical-scan guardband-less tape systems. These systems need a read head with a wider track width than track pitch, so the track profile of the head is important. We analyzed the track profile of MR heads, and found that fluctuations in the reading signal are not an issue. We then mounted the head on a tape-streamer drive and measured the SNR. We found that the MR head provided an SNR which makes it possible to double the areal density with a margin more than 6 dB over that of an inductive head.

回転ドラム搭載型ＭＲヘッドの高密度再生特性

We have evaluated the reproduction characteristics of a magnetoresistive (MR) head for a rotary drum in a helical-scan tape system. This MR head was developed for use in a high-capacity tape storage system that has a high data transfer rate and uses a small cassette. Various experimental thin-magnetic-layer metal evaporated (ME) tapes suitable for the MR head, whose magnetic layer thickness is 0.1 μm or less, have been made, and our evaluation was done using such tapes. We found the output voltage of the MR head was 20 times that of an inductive head, and an areal recording density of 1.2 Gbit/ inch2 was feasible with the combination of the MR head and the thin-magnetic-layer ME tapes. Moreover, the pulse width and CN ratio showed that the optimum value of Brδ, the product of remanent flux density and magnetic layer thickness of the tape, for the trial MR head was from 140 to 220 G·μm.

Head parameter sensitivity study of the intrinsic field reversal time

Studies to establish the key head sensitivity parameters affecting the intrinsic field reversal time are reported. The effect of supply voltage, eddy current damping, head moment, and turns are investigated using the nonlinear, eddy current damped, thin-film write head model proposed by Klaassen and Hirko [IEEE Trans. Magn. 32, 3524 (1996)]. The model is realized using PSPICE circuit simulation. Eddy current time constant dependencies derived by Wood, Williams, and Hong [IEEE Trans. Magn. 26, 2954 (1990)] are used to explore materials with magnetizations ranging from 4πMS=10–20 kG, resistivities of 25 and 125 μΩ-cm and heads with 10–15 turns. Confirmation of the above writer sensitivities has been investigated using a short yoke 37 turn, high moment, low eddy current CoTaZr inductive head. From the experimentally determined model parameters, rise time results are computed for an improved 10 turn writer design. The results are shown to approach or exceed the limiting dynamics of the spin system.

A comprehensive electrostatic discharge control program for magnetoresistive heads

This paper describes a comprehensive electrostatic discharge (ESD) control program for the protection of magnetoresistive and giant magnetoresistive heads. These types of magnetic recording heads are far more sensitive to damage from ESD than the inductive thin film heads which previously dominated head disk drive designs. Sources of ESD damage include people, tools and work stations, packaging materials and the head itself. This document defines procedures for coping with ESD in a thorough, yet cost effective, manner.

Low inductance and high efficiency single-pole writing head for perpendicular double layer recording media

A new type of thin film inductive single-pole head for perpendicular magnetic recording has been developed to provide a writing head for perpendicular double layer media. The head consisted of a main pole, three thin-film conductive layers to drive the pole and a return path pole. A low inductance of around 1.5 nH and a small saturation magneto-motive force of less than 0.025 AT/sub 0.p/ was obtained. The D/sub 50/ was 180 kFRPI with an MR head of 210 nm shield separation. The error rate at 310 kFRPI was 10/sup -6/. Head induced erasure, which is an issue for the single-pole head, was also investigated by experiments and calculations. Around 10% output reduction in 20 Oe stray field was confirmed. Computer simulation predicted an improvement by reducing the permeability of the medium's underlayer.