The ongoing demand for increased storage capacity in ever smaller disk drives is targeting areal densities that are increasingly difficult to achieve with conventional longitudinal recording. The data storage industry is directing extensive resources to develop alternative recording technologies. Magneto-optical recording has been, and remains, a focus of great effort. More recently, MR and now GMR technology, together with low flying sliders, are receiving widespread attention, as means for extending conventional magnetic recording performance. The potential advantages of perpendicular recording have been explored theoretically and experimentally for several decades, and the results of these studies show that the relative benefits increase as the spacing loss decreases and the recording density increases. These principles have guided the development, at Censtor, of ultra low mass heads for continuous sliding contact operation on perpendicular rigid media. This paper discusses some of the issues that must be addressed when integrating Flexhead^® components in disk drives, with particular focus on mechanical tolerance requirements, stray field tolerance requirements, servo electronics and read-write channel electronics.

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  The dependence of the magnetic properties, crystallographic structure, morphological structure and recording characteristics on the angle of incidence were studied on the obliquely evaporated thin Co-O films. The preferred c-axis orientation angle of Co in Co-O films is almost equal to the minimum incident angle (θ min), because the growth at the initial deposition stage around the maximum incident angle (θ max) is very thin and has little magnetization due to oxidization. The Co-O film deposited at θ min of 40° exhibits a maximum output at a recording density of 100kFCI, which is higher by 5dB than that of ME tape for a high-band 8mm VCR.

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  The inclinations of recorded magnetization of a Co-O film and a Co-Ni-O film deposited at the incident angles of 50∼40° and 90∼55°, respectively, against the normal to the film plane are investigated by using the modified Bitter technique. For the Co-O film and Co-Ni-O film recorded at 2kFCI, the inclinations of magnetization from the film plane are 20∼30° and 20°, respectively. The inclination of recorded magnetization coincides with the effective easy magnetization direction on the either film.

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  Obliquely deposited Co-O thin film with carbon protective layer has been developed. In spite of the spacing loss because of its protective layer, its output level is about 5dB higher than hi-8 ME tape, and CNR is about 4dB higher at a recording density of 105 kBPI,. Digital recording characteristics of it were measured by a drum-tester with a ring-type MIG(metal in gap) head. Recording current dependance of phase shift, impulse response and over-write characteristics were measured, and it gave us possibility for high density digital recording without a erasure head.

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  The samples oriented in various out-of-plane directions were prepared. The effect of the particle orientation on the reproduced output wave form and the high-density recording characteristics of the particle media was examined with a ring head. The perpendicularly oriented particle media showed the smallest value of half-height width of the isolated output signal and the excellent high-density recording characteristic in a short wavelength region.

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  The improved magnetic recording system with higher potential were proposed to surpass the conventional systems in recording density. In isotropic recording system, the recording magnetization were arranged obliquely to the film plane. Because of large magnetocrystalline anisotropy, the stability of the recorded magnetization and sharpness of reproducing field were expected to be almost same as perpendicular recording system. In this study, Co-Zn ferrite films prepared by Facing Targets Sputtering (FTS) method at relatively low substrate temperature were used for isotropic media using conventional ring head. The higher recording density such as D₅₀ of 31 kfrpi were obtained.

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  Co/Pt multilayer films developed for magneto-optical recording are studied as perpendicular magnetic recording media. Recording characteristics of Co/Pt multilayer film deposited on a 3.5" magnetic disk substrate, are evaluated using a thin film ring head for recording and compared with those of a single layer Co-Cr-Ta perpendicular recording medium. The results of recording current characteristics and recording density rolloff performance show that the medium is suitable for perpendicular magnetic recording. The medium noise is, however, about two times as large as that of Co-Cr-Ta medium when a high density signal is recorded. Magnetization structure observation indicates that the medium noise is originating from the irregularities of magnetization transitions.

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  Read/write characteristics of the composite media, consisting of perpendicular anisotropy top layer and longitudinal anisotropy underlayer, were investigated focused upon the effect of underlayer magnetization. It was found that the underlayer magnetization affected not only the output but also the mode of remanent magnetization. The reproduced voltage was enhanced well by using the medium with larger magnetization underlayer, whereas the recording density characteristics were better with the thinner underlayer medium. Therefore, it is necessary to optimize the underlayer properties according to the recording density region of operation in order to realize excellent read/write characteristics.

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  Media noise reduction is one of the keys to realizing high density recording. It is believed that longitudinal thin film media have the potential to achieve ultra high density recording with a dependence of noise characteristics on recording density similar to those of particulate media. We studied the source of thin film media noise by changing substrate temperature (Ts) during sputtering. A Co-Cr medium sputtered at 300°C showed a reduction in noise with increased recording density similar to particulate media. Furthermore, the magnitude of DC-erased noise depends on the Ts and is higher in high Ts films. From noise analysis, it was found that the maximum noise frequency of noisy media shifts to low frequency in DC-erased mode. Results obtained from TEM observations and NMR studies confirmed that the low noise media exhibit strong in-grain compositional separation.

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  The isolation of magnetic intergranular coupling is a great importance in the latest high density media. In order to attain this, a small quantity of nitrogen was added to CoCr thin film during sputtering deposition, which brought both increment of coercive force(Hc) and reduction of the coercive force(Hc) dispersion. It is due to a decrease of grain size and magnetic isolation of each grain. Consequently it is confirmed that the reproduced output voltage and D₅₀ is improved, but on the other hand media noise is enhanced with increasing nitrogen addition. The origin of this media noise enhancement will be also discussed.

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  Two mechanisms of overwrite, incomplete erasure and modulation, have been studied quantitatively for Co-based thin film longitudinal recording media with a variety of media parameters using thin film head. For all the media studied, the modulation component is larger than the incomplete erasure component under sufficient write current condition. As MrT or the head-medium spacing increases, the incomplete erasure component does not change, instead, overwrite degrades because of the increase in the modulation component. The increase in Hc affects overwrite performance through the increase in both incomplete erasure and modulation component. The relationship between overwrite and media noise performance is also discussed from the view point of media microstructure.

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  Nonlinear bit shift of CoCrTa/NiFe double layer perpendicular media was studied using a contacting single pole recrding head. The nonlinear bit shift of perpendicular magnetic recordmg was very small for 100 Å and 700 Å head-medium spacings. This result may be due to the large gradient of the total magnetic field where the second transition of the dibit is recorded. The voltage amplitude decreased with increasing head-medium spacing. However, the amplitude of the reproduce voltage was higher than linear superposition for both head-medium spacings. The increase in voltage amplitude may be the result from the reduced transition length parameter for the second transition of the dibit. These results indicate that the double layer media and single pole head are the optimum combination for perpendicular magnetic recording.

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  Overwrite characteristics are discussed from the non-linear transition shift viewpoint The transition shift during write process, caused by the interference of the pre-recorded magnetization, was measured. Based on the transition shift, a model of the overwrite phenomenon was presented. Its validity was demostrated through the experiments. In particular, overwrite dependence on recording density were explained with the model. It was also confirmed that a bi-layered single pole head could improve the overwrite performance by suppressing the transition shift.

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  The Co-Cr films deposited at low Ar pressure, low substrate temperature and moderate biasing voltage on the plasma-free substrates by using the facing targets sputtering apparatus revealed almost perfectly homogeneous microstructure in the surface and interior of the films and were composed of the fine grains with excellent crystallinity. It was found that the addition of third element such as Ta and Re, the exchange of Ar for Kr as sputtering gas and the preparation of the Co-Cr/C, Al multilayers were significantly effective to make the Co-Cr grains finer and more uniform in terms of size and shape.

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  Inter-relationships among medium microstructure, magnetization structure, and recording characteristics are investigated for Co-based longitudinal, perpendicular, and obliquely evaporated recording media. Two types of magnetization irregularities are observed. One is the magnetization transition irregularity which causes magnetic interference between neighboring recorded bits at high linear recording densities. The magnetization interference is the main source of the medium noise for longitudinal recording media. The second type of the magnetization irregularity exists inside the recorded bits which can be observed under all types of recording media. The size of the magnetization irregularity is several times greater than the average size of magnetic crystal grain. The size of the latter magnetization irregularity should be decreased well below the shortest bit length in order to decrease the medium noise and to improve the linear recording density characteristics.

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  Recently it has been shown that the areal density of Co-Cr media for perpendicular recording using a single pole head can be in the order of 5-10 Gbit / inch² [1]. In this laboratory demonstration a track pitch of 0.5 μm (50 kTPI) and a bit length of 260 nm (100 kFRPI) was achieved. Using the same recording set-up, in this paper a MFM image is shown using 300 kFRPI linear bit density and a track width of 0.4 μm. With these densities, icrostructural features like columnar size, compositional separation of Co and Cr, magnetic coupling and reversal behaviour become more and more important. This paper presents experimental results obtained from Co-Cr thin films by using MFM, study of artificially etched micro-strips and measuring anomalous Hall effect from submicron structures, as well as results obtained from magnetostatic and micromagnetic simulations.

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  Several approaches to studying the effect of gaseous rarefaction models in determining steady-state and transient slider orientation are presented. Analytic approaches include an exact solution of the one-dimensional Reynolds equation, singular perturbation calculations for one-dimensional modified Reynolds equations incorporating different rarefaction models, and a scaling analysis to estimate a steady-state flying height. A numerical finite element algorithm incorporating arbitrary slider shape and surface roughness was adapted and made user-friendly. Simulation results are presented for surface roughness simulations and transient responses. Discussion on the development of novel kinetic theory is also given.

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  Two types of perfluoropolyether (PFPE) commonly used as lubricants on magnetic recording media were subject to prolonged ultrasonication in the presence of zirconia particles. The particles were then extracted to collect adsorbed polar products of PFPE chain scission. The extract was characterized by nmr spectroscopy and found to contain low molecular weight scission products of the initial PFPE. These results provide further evidence for mechanochemical scission.

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  Viscous liquid bearings could become a commercially valuable technology for the information storage industry. In the least, the research knowledge gained may be important for modeling lubricants in conventional air bearing drives. Several non-Newtonian empirical models are given to relate the stress to the strain for the bearing liquid. The load bearing capacity, the amount of normal force the fluid can sustain, is calculated for several models by introducing an order of magnitude analysis. Similarly, the power consumption due to frictional forces on the surface of the slider due to the fluid motion is computed.

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  Adsorption features and magnitude for an interaction between lubricant molecules and carbon surfaces were studied to design reliable magnetic disk media. Dangling bonds interact with hydroxyl groups in PFPE diol lubricants as a effective adsorption site. Intra-molecular mobility for a PFPE diol on a amorphous carbon surface was studied using nuclear magnetic resonance (NMR). Thin film viscosities for molecular segments were derived from relaxation time. The hydroxyl segment is anchored on the carbon surface. On the other hand, segments in a main chain show same fluidity as that for a liquid PFPE. This molecular conformation is the feature of good boundary lubricants. Magnitude of the interaction, evaluated by heat of adsorption, increases with an increasing dangling bond density and with an increasing hydrophilic affinity for functional groups in lubricants.

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  A novel contact sliding technique has been developed based on the triboattractivc (TA) contact sliding phenomenon. An essential feature of TA contact sliding is the restoring force effect. The underlying phenomenon is described in terms of experimental results and a feasible physical model explaining the observations is presented. The model involves triboelectric charging and is based on the multiple asperity model used to explain Amonton's law of friction. Some of the performance characteristics of sliders mounted with conventional horizontal recording heads are discussed. This slider technique is expected to be especially suited to perpendicular recording.

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  In a perpendicular recording system, contact recording has been developed in order to minimize the magnetic separation of the head and media. In a system of direct sliding contact, head disk interface metrics such as head wear, media wear, wear debris and others are very important. This paper focuses on the head wear characteristics. Head testing indicated a potential head life in excess of 5 years of continuous operation.

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  Contact type perpendicular recording has high potential for high density recording. However, friction between disk surface and contact area of a head in contact recording induces head vibration, which influences durability and R/W characteristics. We investigated the relation between head vibration and R/W characteristics.

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  Reactivity of hardening agents for particulated magnetic recording media is examined. Trimer-type agents (isocyanurate homologs) had higher reactivity than adduct-type agents. Also, binder films cured with trimer-type agents possessed lower plasticity, indicating better heat resistance than those with adduct-type agents.
  In order to clarify these facts, semiempirical molecular orbital calculations were performed to predict charges on carbon atoms in isocyanate groups. The charges for the trimer-type agent are calculated to be less negative than those for the adduct-type agent, showing higher reactivity.

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  In a helical scan VTR system, the deformation of the magnetic tape due to the magnetic head protrusion affects the recording characteristics. The reproduced waveform envelope changes delicately because of the changes of head-to-tape contact condition from the inlet through the outlet of the helical rotating drum. We proposed a new analysis technique of the head-to-tape contact and the reproduction envelope by the structure/fluid coupled analysis considering the elasto-hydrodynamic lubrication. We have made the computational simulation of reproduced envelope deterioration by the Finite Element Method. The difference between the upper drum rotating mechanism and the middle drum rotating mechanism are discussed.

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  The Iubricity, durability and anti-corrosive properties of metal evaporated tape (ME tape) for digital VCR were investigated. To improve the reliability of ME tape, hard Diamond-Like Carbon (DLC) film is applied as a protective layer on a Co-O magnetic layer. The 10nm DLC film with a smooth and uniform morphology is prepared by a Plasma CVD method using methane and Ar gas. ME tape with DLC shows a stable frictional coefficient against a stainless steel pin. It seems that hard DLC film prevents an increase of the real contact area between ME tape and a stainless steel pin. Hard DLC film also improves still-frame life. The Ms fluctuation of the magnetic layer as a function of the storage period in 60 °C 90% R.H. atmosphere was also investigated. DLC film is one of the most important factors to achieve an excellent anti-corrosive property with ME tape.

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  The project of the recovery of information from strong noise background for the 21st century information storage technology was suggested. Three different Pan - Resonance mechanisms were demonstrated in the ultra high frequency regime where Pan - Resonance is a newly introduced concept. The Pansymmetry of the high frequency regime and low frequency regime was recognized, the importance of puting two Pan - Resonance systems together in a successive way was revealed and explained. Numerical simulation showed that both the “worst pattern” and the all “1”series of the NRZI coding which is the basis of codings could be recovered from a strong noise background completely and with the same system parameters, and the noise was allowed to be approximate white and periodic (with the same and adjacent frequencies, and with different initial phases). For the sinusoidal signal, the information could be recovered from so strong a noise background that the input noise-to-signal-amplitude-ratio was as high as 10. Experiments supporting the results also began.

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  The concept of a two-well potential (TWP) circuit is introduced in this paper. We present a nonlinear circuit working as a special pulse detector which is very useful to extract the signal from noise for narrow track heads. Two mechanisms are discussed for the first time under the condition that the peaks of input signal amplitude are approximately equal to or greater than the critical value which destroys the bistability of the TWP system. Different from traditional stochastic resonance the non-periodic magnetic recording signal is applicable according to our theory for those mechanisms. It is shown that the TWP circuit works efficiently even when the SNR is below 20dB.

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  Pre-embossed rigid magnetic disks that we call PERM disk have been developed to realize high track density recording more than 5000 TPI. Pre-embossed servo patterns, which are magnetized with a 2-step magnetization method, are used as position signals. The PERM disk have realized to follow tracks less than 5 μm pitch using the position signals. It, however, has not been evidenced that a relationship between pre-embossed pattern shape and reproduced signal waveform. In this paper, we have investigated a relationship between the edge angle of pre-embossed patterns and waveform reproduced from magnetized patterns. The horizontal component length of the edge slope of pre-embossed patterns has played the effective magnetic transition length.

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  We discuss Schneider-type write equalization as a robust signal processing method of a write side at digital magnetic recording. Firstly we try to find equivalent recording codes to the Schneider-type write equalizer. Then the performance for each write equalizer combined with partial response maximum likelihood (PRML) methods is evaluated and compared with each other. The results show that the combination of the write equalizer corresponding to IFM-V10 code with PR(1, 1)ML method can achieve the best performance.

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  Bit error rates of inductive thin film heads were evaluated through a PRML (Partial Response Maximum Likelihood) read channel. The objective was to explore the amount of the error rate enhancement obtained by the suppression of the undershoots of the isolated readback waveform of thin film heads, experimentally and quantitatively. The undershoot suppression was realized by the shaping of the pole tips. The error rate was found to be improved by as much as 10² at 26 dB signal to noise ratio, by the undershoot elimination. It was also found that the difference of the error rate between the conventional thin film head and the pole trimmed head became more remarkable as the signal to noise ratio increased.

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  Side writing by the ring head side fringe field has been a big issue to achieve high track density recording. This paper provides research results on the side writing phenomena with a view to achieve longitudinal recording of submicron track width. MFM observation of the recorded magnetization patterns showed that the side written band degraded the write resolution. An analytical simulation considering the non-saturation recording is utilized to reveal the essence of side writing phenomena. The optimization of narrow track recording is also discussed.

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  Perpendicular magnetic recording patterns recorded on a CoCrTa/NiFe medium using a single pole perpendicular contacting head were studied using a magnetic force microscope (MFM). The coercivity of the media was 1300 Oe. The output signal from the recording head tend to decrease rapidly beyond linear density of 3000 fr/mm (76.2 kfci). MFM images of the recorded patterns show curvature of the bit edges, which is characteristic for perpendicular recording. Strong track-edge interactions between overwritten pattern and transitions recorded previously were also observed. These results suggests that the effective track width for readout in perpendicular magnetic recording should be narrower than a total recorded track width. MFM measurements indicate that the maximum linear density sustainable in the demagnetized CoCrTa/NiFe film was limited by the magnetic domain size.

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  The write/read performances of the submicron trackwidth flexhead type single pole heads and the crosstalk of the multitrack array heads were quantitatively simulated using three dimensional finite element method. For heads with very thin poles (down to 0.1 μm), pole saturation is the major problem which limits the maximum writing field of the heads. A pole material with B₅ of up to 2.1 Tesla is required in order to produce the desired write field for good writability on recording media with coercivity of 150 kA/m. The read efficiency of such a head is only about 0.3. The write-read crosstalk level for the array heads is very large.

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  An extremely sensitive system detecting head position for submicron track following is achieved using a MR servo head which is at a right angle with the normal data head and radially magnetised servo patterns which are written by a thin film transverse write head. A dual-stage mechanical actuator system employing piezo-electric bimorph element as a fine actuator and as a bearing spring of the MR composite head is developed. On perpendicular rigid disks, track following on 0.7 μm track has been demonstrated using the new servo method.

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  A concept of a submicron width multi-track head for ultra high track density perpendicular magnetic recording is discussed. Very narrow track of 0.4μm in width is confirmed, judging from a measurement with a magnetic force microscopy. The head configuration for multi-track high areal density recording has been proposed, which consists of submicron-trackwidth write-heads and a high resolution wide-track read-head. C/N ratio of low density signal exceeds 30 dB. D₅₀ is 100 kFRPI; high linear density of perpendicular magnetic recording is not degraded in this scheme. Areal density of 6 Gbit/inch² is demonstrated, and the potential for 13 Gbit/inch² is suggested.

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