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A major cause of magnetic spacing losses in data tape systems is pole tip recession (PTR). This study is an investigation of PTR in a linear data tape recording system and identification of the mechanisms responsible for these effects, but the results have implications for any head where the tape bearing surface is [Al.sub.2][O.sub.3]/TiC, AlTiC. Tape cycling experiments were performed using the linear tape open system as the experimental platform with metal particle tape. All experiments were conducted within a matrix of pressure and humidity, which encompassed the system operating extremes. Atomic force microscopy was used to analyze the surface topography of the heads. Auger electron spectroscopy and x-ray photoelectron spectroscopy were employed to analyze the chemical changes on the surface of the heads and tapes. Environment was found to have a significant influence on the head/tape interface. Head wear and PTR was highest at high temperature and humidity. Water vapor was found to transform the surface layers on the TiC grains in the tape-bearing surface to Ti[O.sub.2]. This process results in the production of Ti[O.sub.2] fragments that become trapped in the recessed pole tip region, acting as three-body abrasive particles. The Ti[O.sub.2] present on the TiC grains and on the surface of heads increases with the water content after cycling against tapes. The hypothesis is supported by the presence of Ti on the poles.

Micromagnetic simulation was used to record and reproduce transverse magnetic recordings.

Permutation codes, introduced by Slepian, were shown to perform well on an additive white Gaussian noise (AWGN) channel. Unfortunately, these codes required large lookup tables, making them quite complex to implement even though the maximum-likelihood decoder is very simple. In this correspondence, we present an enumeration scheme which encodes and decodes permutation codes with low complexity. We concentrate on the use of permutation codes for constructing high-rate codes that satisfy runlength-limited constraints. Wolf showed that permutation codes can be used for runlength constraints and that they have rate that asymptotically achieves the capacity of a noiseless, runlength-limited constrained channel. Wolf, however, gave no efficient encoders/decoder. Our code construction is enumerative, but unlike other enumerative codes, has storage requirements that are a function of the runlength parameters d and k instead of the block length n. In addition, these codes have error detection and correction capabilities. Finally, we use this approach to construct (0, G/I) codes whereby all odd-numbered occurrences of double-adjacent errors are detected. As an example, a 99.2% efficient, rate 496/528, (0, 6/3) code is presented. Index Terms - Enumerative coding, magnetic recording, permutation codes, runlength-limited codes.

A multi-tapped magnetoresistive (MR) stripe has been commercially fabricated as a tape head for evaluation as a potential tracking sensor for magnetic tape systems with dedicated servo. In this approach, two adjacent MR elements sharing a common bias current are each positioned halfway over a single 17 um wide servo track. The head leads provide signals from each of the MR elements which are separated 1.25 um by permanent magnets that provide longitudinal bias. Since this servo configuration uses a differential sensor with a simple square wave tracking pattern, the system can allow self-servo formatting. The evaluation of these heads on a Metrum test stand with 1550 Oe Sony MP media have allowed an estimate of the finest track pitch servo system that could be supported by such a sensor. Two sources of PES error, media noise and PES nonlinearity, have been quantified, and projections of system performance at high tape speeds and narrow trackwidths have been made. With this scheme it seems feasible to reach a 2 um track pitch, but to do so, a non-linear PES fit must be used. Furthermore, to maintain high SNR, the sensor should not be operated in a manner such that it needs to be scaled down in size as the trackwidth shrinks, favoring a so-called multiposition operation scheme. Index Terms - Tape Recording, Tape Heads, Tracking Servos, Position Error Signal, Magnetoresistive Heads.

Shielded spin-valve tape heads with permanent magnet stabilization are described. Final MR of 3.5% is shown on heads with trackwidths of 5 and 9 [[micro]meter], and sensor heights of 0.5, 1.0 and 1.5 [[micro]meter]. Heads are characterized on 1/2[inch] DLT-IV tape up to 180 kfci. For isolated transitions the heads show a [PW.sub.50] of 0.8 [[micro]meter] (pulse broadening due to partial head saturation) and a baseline shift [approximately]10% that can be positive or negative, and is related with shield remanence and transfer curve hysteresis. At 120 kfci, head output for a sense current of 3 to 4 mA is [approximately] 1 [mV.sub.pp] (up to 30% of the output at 30 kfci). At high linear densities, signal loss is 0.24 dB/kfci for a 0.35 [[micro]meter] shield-to-shield spacing ([D.sub.50] of 80[approximately]100 kfci). At low linear densities the head is partially saturated, and above 60 kfci harmonic distortion is lower than -20 dB. Index Terms - magnetic recording/reading heads, magnetoresistive materials and devices, spin valve heads, tape recording.

This paper describes the design, fabrication and performance of an advanced multi-channel tape head for linear digital video applications. The heads were batch fabricated on AlTiC substrates using conventional thin film processing techniques. Each head comprised an array of 16 channels, with each channel consisting of a merged MR reader/inductive writer structure. Two separate head designs were manufactured to investigate improved areal density recording. One type had a channel pitch of 150 um and did not employ a servo scheme. The second type had a channel pitch of 112.5 um and employed a closed loop servo mechanism. After machining and assembly, fully functional heads were employed to write data onto conventional 1650 Oe metal particulate tape media using RLL (1,7) code at a track density of approximately 1350 tpi and a linear transition density of 102 kpbi resulting in an areal density of 138 Mb/[in.sup.2]. The heads exhibited good output, symmetry, resolution and overwrite. The data indicates that with careful process control, it is feasible to manufacture multi-channel tape heads using thin film processing techniques. Index Terms - Tape Recording, Tape Heads, Multichannel Recording, Magnetoresistive Heads

A recently developed, advanced multi-track tape head for operation in a next generation, high performance tape drive is described. This head features full thin film write elements with high moment, cobalt-based pole materials for recording on high coercivity metal particle (MP) tape, together with narrow track, shielded, dual-stripe magnetoresistive (DSMR) read elements. This presentation will discuss the global design philosophy of the head with particular attention to the design and recording performance of the read and write elements in a tape environment. The head is capable of recording 288 tracks on half-inch, MP tape of 1625-1850 Oe coercivity at a recording density of 65 kfci. The system operates with 16 parallel data channels and includes full multi-element active track following servo. The head can be used in a full start-stop mode and read verify on the fly (read-while-write) hi-directional operating modes.

Media transition position jitter noise can be a dominant signal-to-noise ratio (SNR) issue in magnetic recording systems with magnetoresistive (MR) heads and (0, k) PRML channels, since the high MR head 'gain' emphasizes media jitter noise over electronic noise, and (0, k) codes are sensitive to dibit jitter [12]. Time interval analyzer (TIA) instruments are useful for measuring transition jitter (write jitter), since they can separate write jitter from electronic noise (read jitter) with minimal synchronization and speed variation difficulties. This paper analyzes TIA errors due to read channel intersymbol interference (ISI), which occurs even though TIA measurements are made with periodic LF or HF bit patterns at equal bit intervals 'T,' which should be unchanged by ISI. Theory and data show that TIA measurements underestimate jitter by as much as 40% at low channel bit density [D.sub.c] [equivalent to] [P.sub.50]/T [approximately equal to] 1.5-1.8, and overstate jitter at high density. Even though typical TIA jitter measurements are made between nonadjacent pattern pulses, these errors still occur due to ISI by unmeasured neighbor pulses. It is shown that similar errors occur with TIA electronic read jitter noise measurements. At channel densities above [D.sub.c] [approximately equal to] 2.6, channel amplification of transition jitter occurs, which may be a factor in PRML channel bit density limits. Index Terms - Magnetic recording media noise, transition jitter, time interval analysis.

In this paper, we study the statistics of zig-zag transition walls in digital magnetic recording and their relationship to transition noise defining quantities. We provide analytic results that link the statistics of zig-zag transitions to media/recording parameters. The basis of our study is the triangle zig-zag transition (TZ-ZT) model due to its well-defined triangle zig-zag shape and its cross-track stability. The results we derive here, however, are of a general nature, and given the right interpretation, apply to other zig-zag models as well, as we show in the paper. We also provide an interpretation of the cross-track correlation width, linking this quantity to the statistics of magnetized clusters in thin-film magnetic media. The paper concludes by showing how these results can be used in media noise modeling.

The failure mechanisms in a Tape Automated Bonding (TAB) device is analyzed by a 3-D nonlinear finite element analysis. The analysis requires an electrical testing and environmental qualification process to be performed in the unexcised tape carrier. The major part of the polyimide tape in the assembly is also retained during analysis in the TAB device. The analysis reveals that the coefficient of Thermal Expansion (CTE) mismatch between the silicon die and polyimide tape causes the formation of plastic strains in the TAB devices inner leads.

The thermal characterization of the Tape Carrier Package (TCP) involves the consideration of the unenhanced performance of the TCPs. The performance of a 20 millimeter TCP on 8 layer boards is found to be 19 degree C/W. The package thermal resistance is 2 degree C/W. The addition of thermal bias with the use of low profile heat sinks enhances the thermal performance in accordance with the requirements for mobile computing systems.

In this paper, an analysis technique is presented for block oriented data formats in digital tape recording systems. The approach determines format parameters that maximize the information storage density at a specified failure rate. In the process, it is also shown that block interleaving is not beneficial for many systems. Index Terms - ECC, format, interleaving, tape recording

Tape medium noise is extremely important in high-density tape recording systems. Here, AC and DC noise spectra are measured in MP tapes and analyzed assuming tape particle clustering. Measured DC noise of a saturated tape is larger than AC bulk erase noise. At long wavelengths, both spectra are larger than simple theoretical estimates that assume independent particles. At short wavelengths, the measurements are below the theory. Data fitting yields mean cluster lengths in the range of two to four particles. A small percentage of the tape is shown to be in 'pole-free' pairs for the AC noise. Index Terms--Particle clusters, tape medium noise, tape particles.

Simple IrMn spin-valves are investigated for use in high density recording head sensors. Top-IrMn spin-valves of the form NiFeCr(40 [Angstrom])/NiFe(32 [Angstrom])/CoFe(5)/Cu(25 [Angstrom])/ CoFe(30 [Angstrom])/IrMn(80 [Angstrom])/Ta(50 [Angstrom]) were deposited by magnetron sputtering. By tailoring the pinned layer composition at the CoFe/IrMn interface to [Co.sub.60][Fe.sub.40], the exchange bias can be 4 increased above 400 Oe with a GMR amplitude of about 12%. Recording heads were fabricated with total gap thicknesses down to 900 [Angstrom], magnetic trackwidth down to 0.2 [micro]m and stripe height down to 0.3 [micro] m. The transfer curve characteristics are found to agree reasonably well with micromagnetic modeling. The model is then used to predict head sensitivity loss from the combination of insufficient exchange bias and short sensor stripe heights. Index Terms--Exchange bias, GMR sensors, IrMn spin-valves, magnetic recording, magnetoresistance.

We present results from a high-density giant magneto resistive magnetic recording reader using exchange bias stabilization. This novel reader design approach reduces the amount of parasitic resistance, as the sense current is not delivered through high resistivity permanent magnets. Heads were demonstrated to deliver areal densities in excess of 24 Gb/[inch.sup.2]. The electrical performance of these heads, in particular, amplitude sensitivity, micro-track profiles and areal density capability are presented. Reader film properties and manufacturability of this approach are discussed in detail. Index Terms--Exchange tab, patterned exchange, magnetic head, stabilization.

Sputter deposited FeRhN films with a [B.sub.s] value of more than 20 kG were used as high moment flux enhancement layer in the write element in order to achieve a recording density of 63.2 Gb/[in.sup.2]. This layer was disposed between write gap and upper portion of the top pole, which was made of [Ni.sub.45][Fe.sub.55] with a [B.sub.s] of 16 kG. A 36 dB overwrite and nonlinear transition shift of less then -20 dB were obtained at this recording density. A finite element model was used to calculate the longitudinal field and field gradient at the medium location. The results suggested significant increases of both by incorporating the flux enhancement layer. Index Terms--High moment materials, recording demonstration, sputter deposition, write heads.

A set of Co-CoO metal evaporated tapes were prepared with various [O.sub.2] flow rates. Recording tests determined the optimum flow rate and a second set of tapes were prepared at that flow rate with thickness from 33 nm to 103 nm. For thinner tapes the recording carrier to noise ratio is increased while the optimum recording current reduced. Remanence coercivity at 2 ns is about 30% higher than at 100 s and is independent of the thickness. Thermal stability is excellent down to the thinnest tape where KV/kT is still 170. Index Terms--Magnetic recording, ME tapes, thermal stability, time-dependent coercivity.

This paper presents an experimental and theoretical analysis of a number of AC-type magnetization processes similar to those encountered in magnetic recording (AC-biased, DC-biased, partial anhysteresis) on particulate magnetic media. The modeling of these magnetization processes was performed with a scalar Generalized Moving Preisach (GMP) model. The experimental results obtained for a SVHS tape sample are compared with the theoretical ones. A robust identification method for the parameters in the GMP model was used. This method exploits the main static magnetization curves (Major Hysteresis Loop, Isothermal Remanent Magnetization, DC Demagnetization, First Magnetization curve), and the integral Generalized [Delta]M curve, which is sensitive to the value of the moving parameter and to the standard deviation of the interaction field distribution. The agreement between the simulated and measured curves is discussed. Index Terms--AC magnetization processes, Preisach model, recording media.

The mechanism of the tape medium noise is investigated by comparing the magnetization fluctuation resulting from an incremental dc erase process. It is found that the produced magnetization fluctuation displays contrasting behavior for recording heads with two very different gap lengths. A quantitative analysis of the medium noise mechanisms indicates that the sensitivity of the record head to spacing fluctuations explains these differences, and it is concluded that the main mechanism of the medium noise in advanced tape media is the head medium spacing fluctuation due to surface roughness. Index Terms--Media noise, metal-particle media, metal-particle tape.

The continuous stiffness measurement (CSM) technique was used to study the contact stiffness, elastic modulus, hardness, and creep behavior of a metal-particle (MP) tape, metal evaporated (ME) tapes with and without diamond like carbon (DLC) coating and a PET substrate. Nanoscratch and wear experiments were conducted using a nanoindenter with a nanoscratch attachment and a ball-on-flat tribometer, respectively. A good correlation between mechanical properties and scratch/wear damage was found. The relationship between tape structures and mechanical/tribological properties is discussed. Index Terms--Continuous stiffness measurement, magnetic tapes, mechanical and tribological properties, nanoindentation.

The long-term creep deformation and shrinkage characteristics of improved alternate substrates for magnetic tapes are presented. The substrates include two polyesters (PET and PEN) and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; and thinner tensilized-type PET, PEN and ARAMID have recently been used as alternate substrates with improved material properties. The thickness of the alternate film ranges from 6.2 [micro]m to 4.8 [micro]m. The amount of creep deformation is considerably smaller for ARAMID and tensilized-type PET than for PEN. Shrinkage of ARAMID is lower than that of PET and PEN. Based on creep and shrinkage behavior, ARAMID and tensilized-type PET seem to have satisfactory dimensional stability. Index Terms--Creep, magnetic tape, shrinkage, substrate.

The high output at long wavelengths of MP tape causes problems with the nonlinear response of magneto-resistive reading elements. Thinner magnetic coatings would solve the problem but it is easier to add a soft magnetic underlayer to flatten the frequency response. Superparamagnetic maghemite is a suitable material for a particulate soft magnetic underlayer. It has the appropriate particle size and can be prepared in an easily dispersible form. Both the susceptibility and the saturation magnetization achieved in the coating are limited compared with continuous soft magnetic materials. However, the nonlinear saturating effect partly compensates the disadvantage of a low initial susceptibility, while at the same time limiting potential harm to the recording process. Index Terms--Dual coating, magnetic underlayer, metal particles, recording tape.

With the trend toward lower flying heights and increasing storage capacity in the magnetic recording ,industry, the role of contamination and methods to counteract its deleterious effects are expected to become important. One area where the role of contaminants is expected to increasingly affect reliability is long term flyability. This is because volatile and semi-volatile materials in the drive can alter the flying characteristics of the slider during operation because of chemistry at the interface. In this paper, we describe the flyability performance of a head-disk interface system using full body capacitance measurements as a monitor of interface reliability. The principal features observed in flyability tests employing two sources of siloxanes, a model organic compound octamethylcyclotetrasiloxane as well as outgassing from an exposed adhesive tape with a release liner, are described. The deleterious effects of siloxane outgassing that lead to changes in the flying characteristics of the slider and subsequent interface failure are described for disks lubricated with Fomblin Z-dol. Chemical identification of the accumulated material on the slider following flyability testing is described. Strikingly different performance is observed for disks lubricated with the cyclic phosphazene X-1P which shows significantly improved flyability performance. Possible mechanisms that lead to the formation of silica at the head-disk interface for Z-dol based disks and reasons for their absence for an X-1P interface are discussed. [S0742-4787(00)01202-9]

Practical recording channels deviate significantly from the oft-used model based on linearity and additive Gaussian noise. Among the well-known anomalies are partial erasure and transition jitter. In this paper, we first describe a precompensation technique to combat the partial erasure effect. It utilizes the unique property of the maximum transition run (MTR) code wherein all dibits are isolated. The idea is to increase the spacing between the two transitions that make up each dibit. This tends to mitigate the nonlinear amplitude reduction associated with partial erasure. Next, we consider a recording channel that is linear but subject to transition jitter. We modify the hyperplane-based detector known as 3D-110 by introducing data-dependent threshold terms. The overall complexity of the detector is small, yet this modification provides almost 2 dB of improvement relative to the original 3D-110 structure and the extended partial response maximum likelihood (EPRML) method tuned to additive Gaussian noise. Index Terms--MTR code, partial erasure, partial response maximum likelihood (PRML), signal space detection, transition jitter.

We report on a new class of dc-free codes of rate (n - 1)/n, n is odd. Spectral and runlength properties of the new codes have been evaluated by computer simulation. Index Terms--Constrained code, dc-free code, magnetic recording.

This paper presents the theory of pulse-frequency modulation, used for signal transmission in analog video recorders. The paper demonstrates that signal processing in recorders is of the discrete-time type, with the sampling exceeding the Nyquist rate and with restoration of the analog video output from samples in the filter-demodulator. Index Terms--Frequency modulation, magnetic tape recording, pulse position/frequency modulations, video recording.

Hysteresis loop shapes corresponding to particular recorded transition shapes are calculated self-consistently. It is found that the closer a ramp function comes to the shape of the transition, the squarer the hysteresis loop that is needed. Index Terms--Magnetic recording theory, magnetic transition shapes.

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. Index Terms--Co-O, helical scanning tape system, metal evaporated tape, oblique orientation.

Tape surface roughness noise is a large component of medium noise in high-density tape recording systems. Here, the results of tape surface roughness characterization by both mechanical and magnetic measurements are presented. The goal is to measure and compare both RMS roughness variance [Sigma] and roughness correlation length l. The results show that the magnetic recording determination of [Sigma] and l agrees extremely well with the mechanical measurements. Index Terms--Magnetic tape, roughness correlation length, roughness variance, surface roughness.

Recent progress in laser-assisted magnetic recording, which combines optical and magnetic recording technologies, is described in this paper. This study confirms that laser-assisted magnetic recording is a good candidate for high areal density magnetic recording. Improved disk performance was demonstrated in the area of frequency response, media noise, and thermal decay. The improvements in media design include the change in temperature dependence of the recording layer, an increased perpendicular anisotropy, and a thermally efficient layer structure. These improved media properties results in a high linear density and good thermal stability. Index Terms--Disk noise, laser-assisted, perpendicular magnetic recording, thermally-assisted, thermal stability.

Fundamental design considerations of the write head for a hard disk drive with a higher data transfer rate are described. With a shorter yoke, the eddy current dumping can be suppressed effectively. The head inductance is also reduced by yoke length reduction so that the rise time of write current can be reduced. To reduce yoke length, we adopted a double layer coil, which enabled us to increase coil winding turns. With half yoke length and the coil turns increase, we successfully reduced the NLTS by about half. The FIB pole trimming at wafer level can make an appropriate pole shape for generating a highly efficient writing field. Index Terms--Field rise times, high data rate, NLTS, write head, yoke length.

Low media noise and high thermal stability are required to achieve high density magnetic recording. Reduction of magnetic grain size is required in order to minimize transition jitter. However, very small grains become unstable and spontaneously reverse their magnetization due to thermal fluctuations. Future high density ([is greater than] 20 Gbit/[in.sup.2]) recording systems are likely to operate in a media noise dominated environment and could exhibit a certain amount of signal decay. Recording performance degradation caused by media noise and thermal decay is evaluated. Density-dependent amplitude decay is caused by the presence of demagnetization fields and results in increasing level of nonlinear distortions and overwrite degradation. Magnetization decay is accompanied by changes in media noise in an unstable media as determined by the relative contributions of the transition and particulate noises. Experimental measurements suggest, that channel bit error rate degradation in an unstable medium is determined by signal and noise evolution, as well as by pattern-dependent distortions. Index Terms--Amplitude decay, nonlinear distortions, thermal stability, transition noise.

This paper explores the feasibility of implementing conventional magnetic recording technology at densities up to one Terabit per square inch. The key limiting physical factor is the superparamagnetic effect (thermal stability) in the recording medium. Ambient thermal energy can cause the magnetic signals to decay. The requirement for thermal stability over periods of years dictates a lower limit to the size of magnetic grains (switching units) in the recording medium. To achieve the highest areal densities, it will be necessary to use a magnetic recording configuration capable of writing and storing data on very small magnetic grains together with a signal processing system capable of recovering data reliably when each bit is recorded on very few such grains. In addition to these physical effects, there are a number of practical engineering factors that must be considered: tolerances on the head geometry, reliability of head-disk interface, track-following accuracy. In an example system, we use a perpendicular recording configuration since it appears to offer some advantage in terms of maximizing the number of stable magnetic grains per unit area. The readback signals are processed by equalization to a simple binary eye followed by soft detection of a low-rate simple parity check code. The example system approaches a density of 1 Terabit per square inch and allows 3 dB of margin against thermal decay, adjacent track interference, etc. Index Terms--Magnetic recording, media noise, random grains, recording limits, scaling, Voronoi regions.

High [K.sub.u], uniaxial magnetocrystalline anisotropy, materials are generally attractive for ultrahigh density magnetic recording applications as they allow smaller, thermally stable media grains. Prominent candidates are rare-earth transition metals ([Co.sub.5]Sm, ...) and tetragonal intermetallic compounds ([L1.sub.0] phases FePt, CoPtY, ...), which have 20-40 times higher [K.sub.u] than today's hexagonal Co-alloy based media. This allows for about 3 times smaller grain diameters, D, and a potential 10-fold areal density increase ([infinity]1/[D.sup.2]), well beyond the currently projected 40-100 Gbits/[in.sup.2] mark. Realization of such densities will depend on a large number of factors, not all related to solving media microstructure problems. In particular, it is at present not known how to record into such media, which may require write fields in the order of 10-100 kOe. Despite this unsolved problem, there is considerable interest in high Ku alternative media, both for longitudinal and perpendicular recording. Activities in this area will be reviewed and data on sputtered and evaporated thin FePt films, with coercivities exceeding 10000 Oe will be presented. Index Terms--FePt, hard magnet materials, high [K.sub.u] alloys, [L1.sub.0] phases, longitudinal media.

Recent works on perpendicular recording media were reviewed. Co-Cr alloy films are still under improving and show a recording ability of 20 Gbit/[in.sup.2] and beyond. New perpendicular recording media that have high perpendicular anisotropy have been developed. These would be candidate media for ultrahigh density recording beyond 100 Gbit/[in.sup.2].

Simplified Neel-Arrhenius analysis is utilized to determine limiting densities versus SNR for longitudinal and keepered-perpendicular media. Dominant transition noise is assumed and the effects of grain size distribution and storage above room temperature are included. Perpendicular recording potentially exhibits a higher density than longitudinal; for example, at SNR = 20 dB, the limiting densities are approximately 500 and 100 Gbit/[in.sup.2], respectively. Index Terms--Density limits, longitudinal and perpendicular thin film media, magnetic recording, signal-to-noise ratio, thermal decay.

Thermally activated magnetization reversal processes in longitudinal magnetic recording media are the origin of signal decay and time dependence of the coercivity. The former may limit the lifetime of the stored data and the latter determines the minimal write fields at short pulse widths. Both effects depend on the ratio of the reversal barrier and the thermal energy. Signal decay and time dependent coercivity measurements are combined in this paper to experimentally derive a stability ratio, 1/C, as a function of film thickness, recording density and temperature. The experiments are performed with a contact write/read tester using a merged read/write head in physical contact with the sample. Samples are mounted on a variable temperature stage (300 - 390 K) allowing to vary the stability ratios. The samples are a series of CoPtCr recording media with thicknesses from 5.5 nm to 13.0 nm. In the low density limit (500 fc/mm) the onset of thermal decay is observed near [(1/C).sub.0] [approximately equals] 38. Keywords--Magnetic viscosity, magnetic recording, time-dependent coercivity, superparamagnetism.

It is common understanding that superparamagnetic effects will eventually limit the maximum recording density of magnetic hard disk recording. This contribution reviews the theoretical concepts of noise in magnetic recording as well as the concepts of thermally activated magnetization reversal. The theoretical results are contrasted with experimental data. The findings clearly indicate that at some point, signal-to-noise ratio has to be compromised with the thermal stability of the written information. Index Terms -- Magnetic recording, signal-to-noise ratio, superparamagnetic effects, thermal activation, thin film media.

A study of a series of progressively aligned metal particle tape samples has been undertaken. Our data indicates that increasing the orientation, desirable for better recording performance, has been found to increase thermal effects at both DC and high frequencies. The implications of this are that larger head fields are required to write high frequency transitions on more aligned media. The experimental results are compared to the switching model suggested by el Hilo to determine the thermal stability factor [KV.sub.m]/kT of the samples. Index Terms--interactions, magnetisation reversal, metal particles, orientation, pulsed magnetic fields, thermal stability

A self-consistent recording simulator combined with a micromagnetic MR head model is developed to study write equalization in tape recording. The simulation study presented in this paper focuses on the understanding of the magnetization configurations resulted from write equalization and the impact on the write and read nonlinearity. It is found that the write equalization process results in a demagnetized state in otherwise saturated regions. The model analysis combined with an EPR4 channel demonstrates how both write and read linearity of the system are improved. Index Terms--write equalization, tape recording, nonlinearity.

Recording and signal decay characteristics of perpendicular CoCr-alloy thin film media are investigated in comparison with those of longitudinal media. A perpendicular medium shows recording resolution 25-32% higher than that of a longitudinal medium with similar low density output. The medium S/N of a 25nm thick perpendicular medium is comparable to that of a 16nm thick CoCrPt longitudinal medium at high linear densities. The signal decay rate of the high Mr/Ms perpendicular medium is below 0.2% per decade of time for all linear densities. These results and thermal stability considerations based on the temperature dependence of KuV/kT indicate that CoCr-alloy perpendicular recording media are promising to extend the linear density well beyond 400 kFCI. Index Terms--CoCr-alloy, perpendicular media, longitudinal media, thermal stability.

Both dynamic coercivity and thermal decay were quantified by non-destructive spinstand measurements. Media composition was found to significantly affect the stability factor for films having comparable static magnetic properties. Signal decay correlated well with the stability factor as calculated from dynamic coercivity measurements. Monitoring the signal from a harmonic-eliminating pattern is seen to be a robust method for measuring decay. Pattern-dependent amplitude decay leads to enhanced non-linear distortion as thermal decay occurs in complex data patterns recorded at high densities. Index terms--Dynamic coercivity, thermal after-effect, thermal decay, thermal stability.

Dual coated tapes consisting of an active layer containing fine metal powder covering a non-magnetic dummy layer have been widely promoted as perhaps the ultimate flexible recording medium. However, this is not the only interesting possibility opened up by modern double-coating technology. For digital recording, overwrite is an important characteristic. We have found the combination of a high coercivity upper layer of MP with a lower coercivity underlayer to deliver superior overwrite performance. Moreover, it is found that good overwrite ratios can be achieved even when the MP layer is comparatively thick. The combination of thicker upper layer and magnetic underlayer provides higher output in the long wavelength region. Index Terms -- MP tape, dual coatings, overwrite;

To explain the origin of noise in a perpendicular magnetic recording medium, the surface-nucleation model which assumes weak anisotropy on the surface layers is utilized. The model shows that DC-erased noise results from tilting magnetization in the film. The tilting angle is increased by the existence of weak anisotropy on the surface layers. The surface layers with weak anisotropy trigger the magnetization reversal of the whole film and enhance thermal fluctuations. As a result, coercivity at a finite temperature decreases dramatically. It is concluded that control the magnetic properties on the medium surface is very important in order to attain low noise and stability against thermal fluctuation. Index Terms--computer simulation, medium noise model, perpendicular magnetic recording, thermal fluctuation

The demagnetizing field near the top surface of a medium for perpendicular recording is compared with that of a medium for longitudinal recording. On the basis of both the result of this comparison and the output dependence on the medium thickness, a perpendicular medium with a large anisotropy field, [H.sub.k[perpendicular to]] or ([H.sub.k[perpendicular to]]-4[Pi][M.sub.s]), of over 10 or 5 kOe, respectively, is needed to obtain large output and high resolution. Exploiting this large anisotropy field, a composite perpendicular medium with a [([Co.sub.72][Cr.sub.28]).sub.78][Pt.sub.22] layer over a Cr-rich [Co.sub.72][Cr.sub.28] layer was fabricated. By taking advantage of both the large anisotropy in the upper layer and the strong particle interaction in the lower layer, the composite medium with a merged MR head obtained an S/N of 24.0 dB at 200 kFCI and a [D.sub.50] of 205 kFCI, with a 50-nm magnetic spacing. Index Terms--demagnetizing field, perpendicular magnetic recording, composite medium, signal-to-noise ratio.

Read-write tests and magnetic force microscopy (MFM) observations have been performed for Co/Pd multilayer perpendicular magnetic recording media. For a Co/Pd multilayer medium with a nucleation field ([H.sub.n]) of-1.5 kOe and a small slope at coercivity (He), no reversed magnetic domains between the transitions were observed and a low medium noise was also obtained. Moreover, a negligible time decay in magnetization was detected at the remanent state as well as in signals at both low and high recording densities. Index Terms--Co/Pd multilayer media, perpendicular magnetic recording, reversed magnetic domains, medium noise.