Search

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.

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.

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.

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.