Magnetisation distributions in thin film recording heads by Type IIcontrast

The magnetic domain structure of the polepieces of thin-film magnetic recording heads and its variation with drive current and frequency are of interest in understanding the read/write properties of the head. The authors describe the setting up of the synchronous detection mode of type II backscattered electron contrast in a 200-kV electron microscope and its application to the study of domain wall movement in the P2 polepieces of heads with and without the 15-20-μm-thick alumina overlayer in place. Extension of the method to allow evaluation of the changes in magnetization directions under AC drive conditions is described. The authors also demonstrate a novel technique which gives information on the remanent state of the domain structure in the P2 polepiece and its changes under DC drive conditions. It is concluded that these improvements in technique, taken together with the capability of the synchronous detection method to provide information on changes of magnetic structure with depth, mean that this experimental tool will be invaluable in its own right as well as complementary to the Kerr imaging methods     

Batch fabrication of thin film magnetic recording heads: A literature review and process description for vertical single turn heads

Several publications in the past have discussed the potential of batch fabricated thin film heads. Most of these publications dealt with theoretical predictions. Only a few discussed fabrication techniques and reported on the write and read test results. This paper describes a fabrication process for single turn thin film heads of vertical configuration. The process utilizes well known evaporation, plating, and photolithographic techniques. It is simple, inexpensive, and amenable to batch fabrication. Heads fabricated using this process were shown to write and read on a disk, moving at 40 m/s (1575 in/s) with ∼6 Kfr/cm. Dynamic test results reported in a paper by Valstyn and Shew corroborate the earlier prediction. This paper also discusses and compares advantages and disadvantages of the single turn heads of a vertical configuration with those of a horizontal configuration.     

Planar silicon heads/conventional thin film heads - recordingbehavior comparisons

The lower inductance of Planar Silicon Heads (PSH), the output with no undershoot, the low induced noise due to the common mode coil and the P1 equal to P2 with high accuracy make PSH under the same recording conditions of superior performance compared to Thin Film Heads (TFH). In PSH, the uniaxial permeability is parallel to the disc, in contrast to TFH where the high permeability is perpendicular to the disc. This magnetic difference can explain why PSH exhibit smaller PW50. These points will be discussed in this paper     

Recent development of thin film materials for magnetic heads

Recent developments of soft magnetic film materials in the past decade are reviewed. Approximately 20 kinds of alloy systems with high saturation induction of more than 10 kG have been reported in the last decade, although there were only three conventional head materials: Mn-Zn ferrite, Permalloy, and Sendust. A particular focus of the review is nanocrystalline films and multilayer films. Also reviewed are improvements in single-layer homogeneous films of Fe, Fe-Si, Sendust, and Fe/sub 16/N/sub 2/. Almost all the materials reported are Fe-based alloys, and some alloys are nitrogen related: iron-nitride compounds or nitrogen-containing alpha -Fe or Sendust.<>     

Frequency response of thin film heads with longitudinal andtransverse anisotropy

A transmission surface model (TSM) that analyzes the conduction of flux by rotation and wall motion is reported. It has been used to quantitatively compare the predicted performance of thin-film heads with longitudinal and transverse magnetic anisotropy. The TSM analysis predicts that a transversely oriented type of thin-film head can be operated at much higher frequencies than a longitudinally oriented head. In addition, its group delay dispersion is much less. Finally, its susceptibility to wall pinning is an order of magnitude less. Therefore, it is concluded that the traditional aversion of head designers to the longitudinal orientation is justified for frequencies above several megahertz     

High frequency dynamic imaging of domains in thin film heads

A wide-field magnetooptic domain observation system with a time resolution of 10 ns has been developed to study magnetization dynamics in thin-film heads. The instantaneous dynamic response on the top yoke of thin-film recording heads is examined at any chosen instant within the drive current cycle at frequencies up to 20 MHz. Different phase responses from different domain walls in the head are observed and interpreted in terms of hysteretic wall motion, effective field density variation in the head, and wall orientations relative to the flux conduction direction. Two different flux conduction mechanisms associated with two different domain structures in the central region of the head are observed and discussed. Flux conduction in the center of the head by motion of backgap walls and magnetization rotation for domain structures with and without the backgap walls was observed. The domain structure with the backgap walls is probably undesirable because the backgap wall motion may cause a decrease in head efficiency during high-frequency operation and could cause noise during read-back     

Integrated magnetic recording heads

A new type of integrated magnetic recording head has been developed. The head is made completely from thin films by vacuum deposition through a mask. This technology enables us to make many heads in one vacuum cycle. A special study has been carried out on the geometrical forms and on the anisotropic magnetic material. The demagnetizing fields require that we make magnetostatic coupling layers for each magnetic leg of the head. Also, the results indicate that the heads can be used for writing and reading.     

Iron thin film magnetic recording tape by vacuum deposition

A thin-film video tape was formed by sputtering a protective layer on an iron thin film evaporated at an oblique incident beam angle on a plastic base film. The reproduction characteristics show that this tape is suitable for high density digital recording, with high output at short wavelength and low modulation noise. The area packing density can be raised to more than 130 M bits/in². Since the magnetic layer is easily damaged during tape-transport on VTR equipment, its durability requires improvement for practical comsumer products.     

Demagnetization-free longitudinal recording on flexible thin film metal media

The variation of demagnetization effects with media parameters for longitudinal contact recording has been investigated. Co-Re thin film metal media were sputtered onto flexible polyimide substrates. It was found that when the film thickness δ and demagnetizaton parameterB_{r}delta/H_{c}were less than 2 μ inch and 15 μinch, respectively, demagnetization-free longitudinal recording was obtained up to the recording density of 75 KFRPI at the head-to-medium spacing of 3 μ inch. As a result, recording densities of D50over 50 KFRPI were achieved with a 20 μinch gap head. For thicker films with larger demagnetization parameters, i.e.,delta geq 4 muinch andB_{r}delta/H_{c} geq 40 muinch, the longitudinal recording process approached the demagnetization limit. The results show that (with existing head field gradients) improvement in linear density of thin metal media can be obtained by an approximate factor of two before the demagnetization limit is reached.     

Corrosion-resisting Co-Pt thin film medium for high density recording

This paper describes a new material medium for high density longitudinal recording. Sputtered Co-Pt thin films will be shown to have excellent corrosion resistance and magnetic properties. Co-Pt thin films do not need a thick overcoat like plated Co-Ni-P films do, and have higher remanent flux density than ferrite thin films. Co1-xPtx(X=0-0.60) thin films prepared by r.f. diode sputtering have a maximum Hc value near X=20. The Hc, Bs and squareness, for 20 at.% Pt film are 1,100 Oe, 12,000 G and 0.80-0.90, respectively, at 0.1 μm film thickness. These values are not changed over 1-15 Watt/cm²power densities, corresponding to 6-85nm/min deposition rates. Films with more than 28 at.% Pt have no Bs change after immersion in water for over one month, indicating that the films are passive by this test, at least. Ni additions improve magnetic and corrosion properties. There is no Bs change for Co0.070Ni0.010Pt0.020films after immersion in water for over one month. Finally, 51 KFRPI linear recording density was obtained, at D50, using a Co0.70Ni0.10Pt0.20thin film disc with a 0.46 μm gap length head and a 0.12 μm head-medium spacing.     

Application of novel azo metal thin film in optical recording

The absorption spectrum of spin-coated azo metal thin film showed a comparatively large absorption band in the wavelength region (500–600 nm), which matched with the wavelength of the GaAlInP semiconductor diode laser (630–650 nm). The optical recording performance of the film was investigated.     

Head fields of asymmetric recording heads

Head fields of asymmetric recording heads have been measured using 5000:1 enlarged models. From these measurements the head field gradients have been derived and are discussed in view of the role of this quantity in the recording write process.     

Thin-film inductive heads for perpendicular recording

A modified thin-film magnetic head for perpendicular recording in rigid disk drives with improved read/write characteristics, especially at high areal bit densities, is presented. The head on which the modified design is based is described. It combines the advantages of single-pole heads and thin-film heads, writing with the sharp field edge of the leading pole and reading like a thin-film head. To increase the writing efficiency and improve the yield, the sequence of magnetic layers in the head is changed; the second layer of the four-layer head is embedded in the substrate, where it can be placed much closer to the pole tip of the first layer. The improved write capability depends mainly on the position of the embedded layer. In addition, there results an improved magnetic flux guidance from the embedded layer into the pole tip layer, providing the potential for a significant improvement in fabrication yield. The embedded-layer approach also allows a further increase in areal density. The results of read/write tests and the write-wide and read-narrow characteristics are presented     

Irreversible wall motion in inductive recording heads

The effect of signal-induced irreversible domain wall motion on the isolated transition response of recording heads is investigated. An experimental method is presented allowing differentiation between the effects caused by irreversible wall motion and reversible wall motion. The method, utilizing the injection of a small DC current into the head coil, can also be used to determine whether the irreversible motion in a thin-film head occurs in the first pole tip, the second pole tip, or the backgap. The transients observed result from signal-induced irreversible wall motion in the second pole tip. The largest isolated impulse variations occur after saturation of the yoke. In addition, it is found that Barkhausen transitions can occur at or near the top of the isolated impulse (even on its leading edge) as well as after the impulse has decayed, and not only on the trailing edge of the impulse as reported previously. Finally, the authors observe two Barkhausen-noise-free zones, the one at the leading edge being the largest     

Installation for thin film testing with automatic recording of the tension diagram

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 29–30, May, 1989.     

New domain configuration in thin-film recording heads

Kerr microscopy was used to observe the domain structure of Permalloy films that have the same shape as the pole pieces commonly employed in thin-film recording heads. These pole pieces were deposited on thin glass slides, making it possible to observe the domains from both the top and the bottom of the film. It was found that the domain configuration can be quite different on the two surfaces when strain-induced anisotropy is present     

Characterization of magnetic recording heads for drive-specificapplications

Window margin, time interval and waveform analysis techniques that better describe salient on-track performance issues are described. Many of these techniques can be extended to accommodate the addition of off-track and peak shift effects     

Hot-pressed Mn-Zn ferrite for magnetic recording heads

Hot-pressed ferrites have been studied in connection with fabrication of a high quality head material. A two-step hot-pressing technique has enabled the preparation of hot-pressed ferrite with a porosity lower than 0.1 percent and an adjusted average grain size between 0.1 μm and 500 μm. The largest available ingot of hot-pressed ferrite is 120 mm in diameter and 20 mm in thickness. A hot-pressed Mn-Zn ferrite with an adjusted microstructure can be made with a μmof 40 000 and an Hclower than 0.02 Oe. A hot-pressed Mn-Zn ferrite of another composition will have a Bmgreater than 5000 G and a μ0of 700 at 10 MHz. The effect of mechanical working on magnetic properties of hot-pressed ferrites, single-crystal ferrites, and high-density ferrites is also described. The lapping characteristics and the wear problems in a ferrite head of hot-pressed, single-crystal, and high-density ferrite are also discussed.     

Unshielded magnetoresistive heads in very high-density recording

Unshielded magnetoresistive (UMR) heads provide very high signal levels and low noise but, because of their relatively large element height and an insensitive "dead zone" at the sensor edges, they have poor resolution. As a consequence, the signal diminishes dramatically as the recorded density increases and may be as much as 30 dB or a factor of 30 down at very high density. Various techniques have been used to increase the resolution and reduce the "peak-to-bandedge" ratio but they all reduce the bandedge signal as well and hence tend to lower the signal-to-noise ratio. We have found that a peak-to-bandedge ratio of more than 30 dB can be equalized and hence the standard UMR described by Hunt can be used to advantage in very high-density recording. This report describes results obtained with a UMR head reproducing 80 kFCI (3150 FC/mm) signals recorded on Kodak Isomax tape. Bandedge signal and low-density distortion were plotted versus bias field. Surprisingly, maximum high-density signal and minimum distortion occur at about the same bias field. Electronic, thermal, and magnetic noise were measured and tape-noise-limited performance was obtained. Equalized signals from a pseudo-random data sequence were examined with a transition interval analyzer as well as by eye pattern photograph. The transitions were well separated, and the eye pattern was well defined in both phase and amplitude.