Thin layer particulate recording media with a nonmagnetic under layer have been developed with double coating techniques, and their high performance have been confirmed. Such media produce a higher output than single and thick layer media because they have a smooth surface resulting from the under layer smoothness and less demagnetization resulting from the thinness of the magnetic layer. The application of Ba-ferrite particles to thin layer media, in addition to metal particles, has clarified the differences between the characteristics of the two media. The output of thin layer metal media has been improved by up to +9dB compared with the value for reference metal media. Thin layer Ba-ferrite media showed lower noise.
The effects of additive metals ( Nb, Ta, Zr and Pt ) on properties of Co-Cr alloy thin film media have been studied. It was found that perpendicular coercivities ( Hc⊥) decreased monotonically with increasing Zr addition , while Hc⊥ increased and exhibited a maximum value with the addition of 3-4at.% of Nb or Ta and about 12at.% of Pt. Further addition of Pt seemed to decrease the degree of magnetic isolation between particles. Nb addition provided a higher saturation magnetization (Ms) at the maximum value of Hc⊥ than that of Ta addition. The effects of simultaneous addition of Nb, Ta and Zr are also described.
Recorded magnetization structures of CoCrPtTa perpendicular media are obeserved by magnetic force microscopy(MFM). Quantitative analysis of the microscopic magnetization structure is carried out through spectrum analyses of the MFM images. The dependence of MFM signal intensity on wavelength is obtained through Fourier transformation. Several peaks in the Fourier -transformed spectrum are considered to reflect the presence of magnetization irregularities. Average size of the magnetization irregularity decreases with decreasing the magnetic layer thickness. The 50% rolloff densities of MFM signal intensity measured for 25 and 100nm thick media were 200 kFCI and 270 kFCI, respectively.
The magnetic properties, structure and recording characteristics of CoCrTa and CoCrPt single-layered perpendicular magnetic recording media have been investigated. Multilayered magnetic film media with Ti interlayer have smaller crystal grains and lower medium noise than single-layered magnetic film media. Non-magnetic CoCr-alloy underlayers also have an effect on decreasing the medium noise.
CoCrPt/Cr media with Cu interlayer were studied. The R/W characteristics were evaluated by using MR head, and the medium noise was found to be suppressed and the medium S/N was improved by insertion of Cu interlayer. We found that the Cu interlayer led the perpendicular anisotropy of upper CoCrPt layer. We conclude the noise suppression of Cu inserted medium is caused by perpendicular anisotropy of the upper CoCrPt layer.
A Co-Cr-Ta/Ni-Fe double layer tape was fabricated on 10μm thick polyimid film by facing targets sputtering system. The Co-Cr-Ta/Ni-Fe double layer tape showed higher read/write performance than the Co-Cr-Ta single layer tape in not only short wavelength region but also long wavelength region. It suggested that this tape is capable of high recording density of digital VTR.
High density magnetic recording is investigated for a combination of single-layered perpendicular medium and ring-type head. Simulation study shows a possibility of high linear density recording exceeding 400kFCI under a reduced head-medium spacing of less than 40 nm. Experimental results show that the linear recording resolution(D50) increases drastically with decreasing the spacing. D50=173kFCI is confirmed with a highly oriented CoCrPt perpendicular medium and a narrow gap write head under a spacing of 45 nm. Side writing and side erasing can be reduced below 0.2μm by employing a narrow gap write head with trimmed sharp track edge. A new signal processing method is proposed to deal the dipulse reproduced waveforms which result from the combination of single-laryered medium and ring-type head. It is thus shown that the recording areal density can be increased greatly by employing the present recording system.
[Ni81Fe19/Cu]30 multilayers with giant magnetoresistance were deposited using Dual Ion Beam Sputtering apparatus, which can control the crystallite orientation and interfacial structure by using ion bombardment effects. In this study, it was confirmed that the bulk scattering is remarkable for Ni-Fe/Cu multilayers, but the field sensitivity is much influenced by the structures interfaces. The ion bombardment to Ni-Fe thin underlayers for Fe50Mn50 anti-ferromagnetic layers in Spin Valve multilayers was also useful to attain a large exchange bias field.
We have developed FeZrN film which has very high saturation magnetization (Bs=2.0T) and good soft magnetic characteristics. It was found that FeZrN showed good soft magnetic charcteristics and very high saturation magnetization by controlling grain size (D) and lattice stiction(Δ d/d(110)). Single-pole head for PMR (Perpendicular Magnetic Recording) was fabricated using the FeZrN film deposited in the region (D=120Å, Δ d/d(110)=0.4%). The normalized output was 123 nV/μ m·turn·m/s, the overwrite performance was −32 dB, showing the effect of high saturation magnetization material. The film is a very promising candidate for future high density recording head application.
The very high normalized output is obtained by using the single pole thin film head with plane conductors to excite a main pole and to detect the reproduce flux. The main reason for the high output is that the conductors are placed near the mail pole tip. But the effect of eddy current in the conductors is not negligible. The influence of the eddy current in the recording characteristics was examined by numerical simulation. It was shown that the time delay of head field due to the eddy current causes the sharp magnetization transition. Because the influence of the foot of the head field distribution is reduced in the recording process. But the reproduce sensitivity is not increased by the eddy current.
An analysis of recording characteristics on magnetic tape recording systems was described. The magnetization transition parameters were calculated by the simplified vector field model proposed by Bertram et al. . To get accurate results, the head field were generated by finite element methods(FEM) instead of the Karlqvist function. This technique enables us to characterize aspects of the recording process and can be used to show the effect of head-medium parameter changes: head structures, magnetic characteristics of head materials, medium thickness, and medium coercivity. This paper also describes the playback voltage versus recording current for metal film thickness in Metal-In-Gap(MIG) heads and medium thickness, including experimental comparisons.
The Magneto-Resistive Head (MR Head) are adopting to magnetic recording systems for its advantages, like as higher output voltage rather than the inductive thin film head and other reasons. Today, meny companies are manufacturing the MR Head, holding some difficulties. One of the most important thing for the manufacturer is the suppression of noise due to magnetic domain motion. In this paper, I would like to describe the over view of MR Head design and some difficulties for manufacturing.
CoCrPt/TiCr perpendicular recording media sputter deposited on 230°C SiO2/Si substrates with 2 mTorr argon pressure have strong c-axis vertical orientation. Increasing argon pressure during CoCrPt deposition to 15 mTorr increases particle separation, which improves media signal to noise ratio, but decreases preferred orientation, resulting in poorer high density performance. Improved signal to noise ratio and high density performance are obtained using a 2-layer CoCrPt layer. A 2 mTorr argon pressure CoCrPt nucleation layer poduces strong c-axis orientation that is maintained during continued, particle separating growth at 15 mTorr argon pressure. TiCr underlayers have ∼5 nm particles, poor orientation and are not columnar. Nevertheless, they improve CoCrPt c-axis vertical orientation. Low argon pressure during TiCr deposition maximizes CoCrPt orientation, but particle separation increases with increasing pressure. A TiCr bilayer having a high pressure growth layer followed by a thin low pressure template produces improved improved performance of the subsequent CoCrPt layer.
Optical properties of Fe-SiO2 composite film was measured by ellipsometry. The observed complex reflectivity ratio Rp/Rs were compared with those calculated from anisotropic effective dielectric constant by a model that fine Fe metallic ellipsoids were precipitated in dielectric matrix (SiO2). Volume fraction is in good agreement with those from magnetization measurement, but differs from that of XMA. It is considered that a part of Fe particles of Fe-SiO2 composite film are oxidized as deposited. Depolarization factor (=demagnetizing factor) of metallic phase is 0.7-0.8, in other words short axis of Fe particles is normal to the film plane and demensional ratio (long axis/short axis) is about 2.
Acicular barium ferrite fine particles doped with Co2+ ions and Ti4+ ions were prepared by a conventional sintering method. We investigated crystal structure and magnetization mechanism of the acicular BaCoXTiXFe12-2XO19 (X=0 to 1.0) fine particles. By the TEM observation for acicular BaCoXTiXFe12-2XO19 fine particles, it was clarified that all kinds of acicular BaCoXTiXFe12-2XO19 particles consisted of some grains and their c-axis were aligned along the short axis of the acicular particle. Moreover, magnetic tapes coated with these particles and binders under a magnetic field of 7 kOe were prepared to investigate the magnetization mechanism of them. It was confirmed that magnetization mechanism of acicular BaCoXTiXFe12-2XO19 fine particles was rotation magnetization by the measurement of angular dependence of their coercivity.
Ba ferrite films with well c-axis orientation and magnetic characteristics were deposited on ZnO underlayer at substrate temperature Ts from 475 to 600°C in the gas mixture of Xe 0.10 Pa, Ar 0.08 Pa and O2 0.02 Pa using the facing targets sputtering apparatus. The film deposited at Ts of 600°C was composed of BaM ferrite and spinel crystallites and had saturation magnetization 4πMs of 5.1 kG and perpendicular anisotropy constant Kul of 4.23×105 J·m-3 which were larger than those of bulk BaM ferrite of 4.8 kG and 3.30 × 105 J·m-3, respectively. C-axis orientation was observed even for the film deposited at low Ts of 475°C and its values of 4πMs, perpendicular coercivity Hc⊥ and in-plane one Hc// were 4.7 kG, 2.38 kOe and 0.19 kOe, respectively.
Cobalt ferrite films with perpendicular magnetic anisotropy were fabricated by facing targets sputtering and their magnetic properties and recording characteristics were investigated. When a film was deposited at PO2=0mTorr and annealed at Ta=300°C, the (CoFe2O4)-(Co-CoO) composite film with perpendicular magnetic anisotropy was prepared. The composite film which had Hc⊥=1.5kOe, Hcr=3.5 and Sq⊥=0.46 was superior to a CoFe2O4 single phase film in magnetic properies. Furthemore the recording characteristics of (CoFe2O4)-(Co-CoO) composite film disk were measured. The reproduced waveform was a dipulse type, so that the film had perpendicular magnetic anisotropy. The value of D50 was 48.5kFCI.
Micro-structure of obliquely evaporated Co-CoO film is investigated by using high resolution transmission electron microscope (TEM) and fast Fourier transform (FFT) technique. Power spectrum image, corresponding to diffraction pattern, is obtained by FFT for TEM image. Lattice images of Co (002) and CoO (111) are reconstructed by inverse FFT for selected Fourier transformed data. It is found that the Co-CoO film contains very small Co particles from 4 to 6 nm in diameter.
Effect of a liquid nitrogen shroud for the deposition of a Ni-Fe-Nb soft magnetic layer for a perpendicular magnetic recording medium is investigated. The shroud has an advantage to remove water from sputtering atmosphere, quick pumping as well. Consequently, a deposited film shows both good crystallinity and smooth surface, which are suitable for the under layer of the recording medium.
The signal-to-noise ratios (SNR) of various partial response maximum-likelihood (PRML) systems in perpendicular magnetic recording using a multi-layered main-pole head are studied. Among the PRML systems having transfer function (1+Dp)(1−Dq)(1+Dl)m represented by a delay operator D, several PRML systems which show the large SNR at the discrimination point are found by utilizing the minimum Euclidean distance between all possible pairs of sequences at the input of Viterbi decoder. The required SNRs of the PRML systems to achieve a bit-error rate of 10−4 are also obtained by computer simulation. It is shown that the PR(1,1,0,0,0,0,−1,−1)ML system with a conventional decoder exhibits the excellent performance and the system with a simplified decoder still shows the good performance at high recording density.
Extremely high areal density utilized submicron trackwidth recording was proposed. To overcome the difficulty in tracking servo to follow the narrow track, multi-track parallel recoding is effective with a wider track read haed. A new encoding/decoding scheme introducing multi-level partial response is investigated. It is demonstrated by an experiment that recorded information on two tracks can be descriminated even with a single widetrack read head by means of this scheme.
Equalizations in the inter-track orthogonal coding which has been recently proposed to remove inter-track interference were studied. When PR4 is used, lower bit error rate is obtained at higher linear densities. On the other hand, when integrated equalization is used, much larger signal-to-noise ratio is obtained than that in conventional NRZ coding.
We propose a novel servo technique in which the Position Error Signal (PES) of head is continuously extracted from data signals which is coded by a modified ITOC (Inter-Track Othogonal Coding) method. Bit-interferences in the PES for high linear density recording can be supressed by averaging. This servo technique is considered to be effective for magnetic recording systems which use submicron track width and/or DWCR (depersive writing and collective reading).
Deposition of carbon films by fasing targets sputtering on substrates at liquid nitrogen temperature and control of the angular distribution of the depositing particles were attempted to improve the protective properties of diamond like carbon films(DLC films). The films deposited at the liquid nitrogen temperature has much higher density and higher hardness than the film deposited at room temperature has. Removal of deposition particles with high incident angles were found to be effective to increase the density and hardness of the film. These facts indicate that a decrease in substrate temperature to liquid nitrogen temperature and the suppression of self shadowing effect by removing the deposition particles with high incidence angles were effective to obtain a DLC film with high density and high hardness.
Results obtained on current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effect show low-field magnetoresistance change ratio as high as 30%, superior to conventional current-in-plane (CIP) GMR effect. A storage mechanism in CPP GMR artificial lattice is also found, similar to that in CIP structure. Based on this storage mechanism, we designed an advanced perpendicular GMR random access memory (RAM). These CPP GMR elements provide an excellent means of storing information as a remanent magnetization on the hard components with high density, whereas low impedance output drivers offer extremely high signal-to-noise ratio (SNR) readout signal at low power, by suppressing such as Johnson noise from normal metal. In other words, it is expected of that the problem of low SNR of signal, existing in magnetoresistance random access memory for a long term, will be solved by our scheme.
Magnetoresistive/Inductive head designs and recording characteristics were discussed in perpendicular magnetic recording. Recording by two sheets of shield showed good overwrite performance in a shielded type MR head. The head had high D50 of 100∼135kFRPI with the shield-to-shield gap of 0.5∼0.7μm. However when the recorded bit-length became shorter than the shield-to-shield gap, the shield had little effect on the medium stray field. In unshielded MR head, though large output was obtained in low density region, the output gradually decreased with increasing the recording density. However the decrease rate was much lower than that of the decrease reported in longitudinal recording. In result, the shielded type and even unshielded type MR heads offered high density recording characteristics in the contact state.
A magnetoresistive head (MR head) is applied to the reproduced process in perpendicular recording in comparison with longitudinal recording medium. High readback voltage by a factor of nearly two is obtained in associate with its large recording magnetization. in a perpendicular medium. D50 of the perpendicular medium is the same as the longitudinal one, which is thought to be resolution limitation of the MR head.
We evaluated read/write characteristics of perpendicular magnetic recording. This measurement was carried out using an ID/MR composite head (composed ring type ID head and shield type MR head) and double layered perpendicular magnetic media. It was found that the perpendicular magnetic recording using ID/MR head produced higher signal output and superior offrack performance, compared with conventional longitudinal recording.
We investigated the possibility of realizing the high-density recording by using a single-layer perpendicular medium and a merged MR head. The MR head output signal with the perpendicular medium was 50% larger than that with a longitudinal medium. A maximum D50 value of 100 kFCI was obtained for a medium with an optimum thickness of 300 nm. Media with thickness of over 300 nm had increased media noise, and the output was saturated at 300 nm. We expect to realize highlinear density recording by improving the medium's perpendicular anisotropy.
Recording characteristics of perpendicular-longitudinal composite media with high coercivity underlayer with combination of ring-type heads were systematically reviewed on the basis of own investigation. The reproduced voltage of the composite media was higher than simply superposition of the output of perpendicular layer and longitudinal underlayer. It was found that the residual magnetization mode of composite medium was "phase synchronization mode," which formed horse-shoe shape composed with "strong perpendicular magnetization" region of perpendicular layer and longitudinal magnetization of underlayer. Moreover, the magnetization state can be controlled by medium and head parameters, indicating the importance of the optimization of medium and head parameters.
Future trends for high density video data storage of 1 Tbits/in3 in multimedia service would be discussed in this paper. Magnetic tape With Co-Cr-Ta/Ni-Fe multilayer has been prepared by using facing targets sputtering system. Read/write characteristics of this tape has been investigated using conventional VTR. It has been proven that the tape should be highly efficient in high density recording of 1 Tbits/in3.