Co-Cr Perpendicular Recording Media Research Articles

Noise Properties of an Electroless-deposited CoNiReP Perpendicular Magnetic Recording Medium and a Perpendicular / Longitudinal Composite Medium

Noise properties as well as read / write characteristics of a CoNiReP single-layer perpendicular magnetic recording medium and a perpendicular / longitudinal composite medium are investigated by using a merged ring-type write / MR read head. The reproduced voltage of the composite medium is higher than the single-layer perpendicular recording medium in the region of lower than 100kFRPI. The noise power of the CoNiReP single-layer perpendicular recording medium is almost independent of recording density, similar to a CoCr perpendicular recording medium prepared by sputtering method. The noise power of the composite medium was lower than the superposition of the noise power of the longitudinal magnetization underlayer alone taking account of spacing loss and the noise power of the perpendicular magnetization upperlayer alone. But no noise reduction was obtained in the case of using narrow gap recording head. In order to realize excellent noise properties as well as read / write characteristics, it is necessary still more to clarify the effect of head and medium parameters and to optimize these parameters.

Co-Cr perpendicular media with semi-soft magnetic and ultra thin back layer for ring-type head

In order to use a ring-type head instead of a single-pole head, a newly designed Co-Cr perpendicular recording medium has been investigated in terms of its recording properties and medium design. A hard disk system with a non-flying metal-in-gap (MIG) head was used for the test. By setting an ultra-thin semi-soft back layer at the back side of the Co-Cr layer, the reproduced pulse shape has been dramatically improved, showing single peak pulses different from the so-called di-pulses obtained for a single-layer Co-Cr medium. This Co-Cr/Fe-Co composite medium was compared with a longitudinal medium of Co-Cr-Ta/Cr with regard to the spacing effect of the output voltage and the density response. The new composite medium showed recording properties superior to those for either the longitudinal medium or a Co-Cr single-layer medium for a very small value of head-medium spacing.

Behavior of Soft Magnetic Backlayer in Recording and Reproducing Process on Perpendicular Magnetic Recording Media

Double layered Co-Cr perpendicular recording media were studied with respect to effect of a Ti thin intermediate layer between the Co-Cr and Ni-Fe layers on recording and reproducing characteristics. The increase of the output voltage by introduction of the Ti layer was explained by the increase of the effective permeability of the total system of the perpendicular head and back layer of the D.L. medium. It was found that the highly permeable back layer achieved by using the Ti layer induces a broadened waveform and an increase of peakshift of reproduced pulses. We concluded that media without a Ti layer are superior to those with a Ti layer with respect to the recording resolution.

On design of Co-Cr perpendicular recording media for usage of a ring-type head

Co-Cr double-layer media were studied in order to improve perpendicular magnetic recording by using a ring-type head. A very thin semihard back layer (only 100 AA) with a high saturation moment showed a dramatic increase of reproducing output over a wide density region, while the recording sensitivity was also improved. The reproduced waveform with a sharp single peak desirable for actual systems occurs with peak shift as small as that for a single-layer Co-Cr medium. It is supposed that these improvements are caused by reduced demagnetization in the recording process. Design concepts of the media are discussed. >

Magnetic Properties of Narrow Stripe Co-Ta-Zr Amorphous Films

The magnetic properties of narrow stripe Co-Ta-Zr amorphous films, with induced anisotropy across the stripe width, have been investigated. The permeability of the films decreases with decreasing stripe width. This can largely be explained by the increased demagnetization field which may reduce the initial anisotropy and rotate the easy axis to a direction perpendicular to the initial easy axis, or may change the magnetic domain structure. Stress in the film may act to enhance or retard this effect, depending on the film's magnetostriction constant. It is therefore important to determine an appropriate magnitude for the induced anisotropy and to choose a proper combination of the magnetostriction constant and the substrate thermal expansion coefficient. Utilizing such knowledge, thin film heads with a 5 μm track width have been fabricated. A reproduced voltage of 380 μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PP</sub> /mm-turn-m/s has been obtained in combination with Co-Cr perpendicular recording medium.

狭ストライプＣｏ‐Ｔａ‐Ｚｒアモルファス膜の磁気特性

Magnetic properties of narrow stripe Co-Ta-Zr amorphous films with induced anisotropy across the stripe width have been investigated. Permeability of the films decreases with a decrease in the stripe width. This can largely be explained by the increased demagnetization field which may reduce the initial anisotropy and rotate the easy axis to the direction perpendicular to the initial easy axis, or change the magnetic domain structures. Film stress may act positively or negatively on this, depending on the film's magnetostriction constant. It is, therefore, essential to determine an appropriate magnitude of induced anisotropy and to choose a proper combination of magnetostriction constant and thermal expansion coefficient of the substrate. Utilizing this knowledge, thin film heads with 5μm track width have been fabricated. Reproduced voltage of 380μVpp/mm · turn · m/s has been obtained when operated with Co-Cr perpendicular recording medium.

Single-turn perpendicular thin film heads

This paper describes the thin film heads, intended for use with CoCr perpendicular recording media, which were designed to bring forth highest possible efficiency both in ring-type and pole-type constructions. The heads are of single-turn structure to minimize the yoke length, and all the magnetic films are deposited on substantially the flat planes to avoid magnetic degradations. By employing such scheme, both ring-type and pole-type thin film heads are shown to have efficiency comparable to that of VHS-type ferrite video heads.

Magnetization Reversal Mechanism of Co-Cr Perpendicular Magnetic Recording Media

In order to investigate the mechanism of magnetization reversal in Co-Cr perpendicular recording media, the angular dependence of the hysteresis loss was investigated. For a double-layer medium consisting of a Co-Cr layer and a Permalloy backing layer, it is easy to show that rotational magnetization reversal occurs in the Co-Cr layer. Judging from both the angular dependences of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and of the hysteresis loss, the initial growth layer and the columnar structure layer in Co-Cr sputtered film were found to undergo magnetization reversal by domain wall motion and by rotation, respectively. Other Co-Cr films with different M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> and H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> values were also studied with respect to the prevailing mechanism of magnetization reversal.

Studies of magnetization reversal mechanism of perpendicular recording media by hysteresis loss measurement

Magnetization reversal mechanism of Co-Cr Perpendicular recording media, was investigated by means of hysteresis loss as a judging criterion. Hysteresis angular variations were compared between typical reversal models and experimental results for various Co-Cr films. It has been found that if we assume partial orientation of the easy axis in the film plane as well as main perpendicular orientation, the experimental data agree very well with the theoretical angular dependences. The volume of in-plane easy axis component could be estimated quantitatively for the films with various saturation moment, coercive force and thickness. It was concluded that almost hysteresis angular dependences of the Co Cr films can be explained by curling reversal mode.

Wear resistance, mechanical strength and microstructure on sputtered CoCr perpendicular media

Wear resistance for sputtered CoCr perpendicular recording media has been investigated. Wear resistance and mechanical strength (tensile strength and Young's modulus) have been measured for CoCr (0-33 at% Cr) films deposited under various sputtering conditions. Furthermore, their correlations to CoCr film microstructures have been studied. The wear resistance on the CoCr films strongly depends upon the mechanical strength, and their relationship can be explained in terms of Archard's adhesive wear theory. Wear resistance and mechanical strength for CoCr (5-33 at% Cr) films decrease steeply at high sputtering Ar pressure. However, those for pure Co films are independent from sputtering pressure. Microstructure analyses for CoCr and pure Co films indicate that a main factor reducing the wear resistance and the mechanical strength is Cr segregation in the CoCr films.

Co-Cr垂直磁気記録媒体の磁化反転機構

In order to investigate the mechanism of magnetization reversal in Co-Cr perpendicular recording media, the angular dependence of the hysteresis loss was investigated. For a double-layer medium consisting of a Co-Cr layer and a Permalloy backing layer, it is easy to show that rotational magnetization reversal occurs in the Co-Cr layer. Judging from both the angular dependences of H c and of the hysteresis loss, the initial growth layer and the columnar structure layer in Co-Cr sputtered film were found to undergo magnetization reversal by domain wall motion and by rotation, respectively. Other Co-Cr films with different M s and H c values were also studied with respect to the prevailing mechanism of magnetization reversal.

Wear Resistence of Co-Cr Perpendicular Recording Media with Oxided Surface Layer

A Co-Cr perpendicular recording film was fabricated with an oxidized surface layer, as an alternative to the unsatisfactory conventional technique of coating a lubricant on the surface of Co-Cr film, and its friction and wear characteristics were investigated. The friction force of the Co-Cr film with the oxidized surface layer was found to be below one half of that of the Co-Cr film without the oxidized surface layer. Furthermore, the oxidized surface layer has considerably improved the wear resistance of Co-Cr media.

Noise characteristics in Co-Cr perpendicular recording media

Noise characteristics in Co-Cr and Co-Cr/Ni-Fe perpendicular recording media were theoretically analyzed, based on an uncorrelated particle magnetization model. The analyzed results were compared with experimental results. Marked differences in noise spectra were found between single layer and double layer media, especially in the long wavelength region. The measured noise and signal spectra in a Co-Cr/Ni-Fe double layer medium were close to the numerically analyzed values for perpendicular magnetization, rather than for longitudinal magnetization. This indicates that the magnetization in the Co-Cr layer is directed almost perpendicularly. Furthermore, the measured noise power decreased with increasing the medium perpendicular anisotropy, which is closely related to the medium crystal orientation. As a conclusion, noise from Co-Cr perpendicular recording media is attributed to the medium grain magnetization direction dispersion, where the magnetizations are almost perpendicular to the medium surface.

Direct observation of magnetically distinct regions in Co-Cr perpendicular recording media using ferromagnetic resonance

We have used a 30-GHz resonant cavity spectrometer to record the ferromagnetic resonance (FMR) spectra characterizing several Co-Cr films. These films, 18–22 at. % Cr in composition, were characterized by net mean anisotropy K̄ extending from negative to positive in range. K̄ and M̄S are measured by a torque magnetometer (TM) and a vibrating sample magnetometer (VSM). FMR was used to measure the relative amounts and the corresponding 2K/MS and γ values of each of the magnetic constituents in a given specimen. Using integrated FMR intensities and corresponding 2K/MS, a reasonable correlation between the TM/VSM data and FMR was achieved. An initial study on four films indicates that poorly aligned specimens (Δθ50≂8°) are composed of several distinct magnetic constituents; well-aligned specimens (Δθ50≂2°) are characterized by a single constituent. Further, samples with larger Δθ50 all seem to be characterized by at least two constituents in common: one at 2K/MS≂0, the other at 2K/MS ≂−4πMS. This research, we believe, represents the first known confirmation by FMR of positive anisotropy in such Co-Cr films.

Co-Cr perpendicular recording medium by vacuum deposition

Magnetic and structural properties, crystal orientation, resistance to atmospheric corrosion, and depth profile of vacuum deposited Co-Cr perpendicular anisotropy films are presented. In contrast to the RF sputtered Co-Cr films having a rather small deposition rate, the present study confirms the applicability of vacuum deposition to the preparation of Co-Cr perpendicular anisotropy films at a deposition rate up to 6000 A/sec. It was found that films with relatively high magnetization and coercive force could be made which at the same time exhibited good corrosion resistance.