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We compare several different detection and equalization methods for bit patterned media recording channels .We consider a scheme that utilizes a joint-track equalization technique followed by a Viterbi detector. For certain recording densities, simulation results show that it has essentially the same performance as an optimal detector but with reduced detection complexity. Furthermore, it outperforms another scheme of the same complexity previously described in the literature. [ABSTRACT FROM AUTHOR]

In high density perpendicular magnetic recording channels, nonlinear transition shift (NLTS) is one of the distortions that can degrade the system performance. Write precompensation is a standard method used to combat the negative effect of NLTS. In this paper, we present an analysis of the bit-error-rate (BER) for perpendicular recording systems with NLTS and write precompensation. Media jitter noise and additive white Gaussian noise are also considered in the model. A BER lower bound is derived, as well as a more easily computed estimate of the bound. The write precompensation values that numerically minimize the estimate of the BER lower bound prove to be very close to those found using Monte-Carlo channel simulation. We then apply these methods to the design of multilevel precompensation schemes, for which the optimization of precompensation values by Monte-Carlo channel simulation is computationally infeasible. The results show that for higher recording densities subject to increased ISI and noise, the use of more complex precompensation schemes does not significantly improve the system performance. [ABSTRACT FROM AUTHOR]

We present a semi-analytical approach for the analysis of synchronization in bit patterned media (BPM) recording. The analysis is based on full numerical micromagnetic calculations of the reversal surfaces of separate BPM element. These reversal surfaces arc used to define writing window zones for correct recording in BPM element arrays. The simulations show that staged media lead to improved performance and larger writing window zones (WWZs). The presented model and results are important for estimating BPM designs in terms of density, bit-error rates (BERs), and performance. [ABSTRACT FROM AUTHOR]

Precessional reversal in composite patterned media elements has been studied for various applied field parameters. The decrease of the percentage of the elements covered by the applied field leads to a rapid increase of the reversal field and decrease of the critical rise time required for precessional reversal. For weak and strong applied fields, the reversal time respectively was found to decrease and increase with an increase of the applied field strength and decrease of the rise time. For certain (large) values of the applied field strength and pulse duration bands of non-reversal can be obtained. This behavior is associated with multiple precessional oscillations between two equilibrium states. Such oscillations can be eliminated by properly choosing the field pulse duration and element damping constant. [ABSTRACT FROM AUTHOR]

In high-density perpendicular magnetic recording channels, nonlinear transition shift (NLTS) is one of the distortions that can degrade the system performance. Write precompensation is a standard method used to combat the negative effect of NLTS. In this paper, we propose a modified pattern-dependent noise predictive (PDNP) detection algorithm for use on channels with electronics noise, transition jitter noise, and NLTS. We show that this detector can offer significant improvement in bit-error-rate (BER) compared to conventional Viterbi and PDNP detectors. Moreover, the system performance can be further improved by combining the new detector with a simple write precompensation scheme. [ABSTRACT FROM AUTHOR]

A dual-layer patterned element magnetic recording medium design is presented that is expected to satisfy areal densities at 10 Tb/in². Each element consists of a small high anisotropy initial layer on top of which is deposited on an exchange-coupled soft layer of approximately equal thickness that extends in the recording direction almost to an adjacent element. This design has two distinct advantages. Reversal by precessional switching will occur for realistic record head field rise times (100-200 ps). Thermal stability for such small elements is maintained by hard section anisotropy fields that are an order of magnitude larger than the reversal field. Here, reversal mechanisms and system design are discussed in detail. [ABSTRACT FROM AUTHOR]

The article focuses on the development of an expression for estimating error rates in perpendicular magnetic recording systems. It examines an estimation of the probability of error for a dominant dibit error event, with a variety of parameter changes used to determine the error rate. It mentions that noise includes stationary white Gaussian electronics noise, as well as nonstationary colored medium transition noise. It discusses an expansion of the model to include additional noise effects.

It is conceivable that early generations of patterned media will utilize read heads whose dimensions are several times larger than an ‘island’ of magnetization. For such a scenario, we propose a ‘multiple islands per read head’ model where the output from the read head is a function of the magnetization from several independently written tracks of islands. In particular, we focus on a ‘3 islands per read head’ model where the output from the read head is a function of the magnetization from three independently written tracks of islands. The readback signal is determined from a finite track-width magnetoresistive (MR) head model using reciprocity calculations, and two noise sources—island position jitter and AWGN electronics noise—are considered. By sampling the noisy signal at intervals corresponding to the down-track island separation, we obtain a discrete-time readback channel model whose performance is obtained under maximum-likelihood sequence detection. [ABSTRACT FROM AUTHOR]

To optimize a high-density magnetic recording system, one needs to know the tradeoffs between various components of the system including the read/write transducers, the magnetic medium, and the read channel. In this paper, we consider a channel model characterized by three parameters: the replay pulse width T50, the transition jitter noise standard deviation σ J,, and the signal-to-electronic-noise ratio SNRWG. We utilize information-theoretic tools to determine the acceptable region for the channel parameters T50 and σ J when optimal detection and linear coding techniques are used. This paper is an extension of a similar analysis for a system that utilized a minimum mean-squared error (MMSE) equalizer, a Viterbi detector, and a Reed-Solomon (RS) code. Our main conclusion is that there is a considerable potential gain to be achieved by using improved detection and coding schemes as compared with the present system. [ABSTRACT FROM AUTHOR]

In a perpendicular magnetic recording system, advanced read/write transducers, magnetic media, and signal processing techniques are combined to achieve the highest possible storage density, subject to severe constraints on reliability. This paper proposes a quasi-analytic methodology for exploring the complex design tradeoffs among these system components. We use a simple channel model, characterized by three parameters: isolated voltage pulse width, transition jitter noise variance, and additive electronic/replay head noise power. The system incorporates generalized partial-response equalization and maximum-likelihood detection, along with a Reed-Solomon error-correcting code characterized by its code rate. We calculate a family of ‘design curves’ from which we can determine, for a given set of channel parameters, the maximum user density that can be achieved with a specified codeword error rate, along with the corresponding code rate. The design curves can also be used to determine the acceptable range of channel parameters consistent with a target user density and codeword error rate. [ABSTRACT FROM AUTHOR]

In this paper, we use micromagnetic simulation to study the switching field reduction and the switching field distribution in polycrystalline thin-film media. We first show that, for the coupled magnetic particles, the switching field of the high-anisotropy particle is reduced as a result of the exchange coupling with the low-anisotropy particle. The switching field reduction increases almost linearly with the anisotropy difference between the coupled particles. An optimal exchange exists that gives a maximum switching field reduction. This switching field reduction is more severe for a small applied field angle; therefore, the angular sensitivity of the switching field is reduced compared to the Stoner-Wohlfarth relation. Detailed micromagnetic simulations also show that in polycrystalline thin-film media, because of the variation and the reduction of the magnetic properties at the grain boundaries, the media coercivity can he reduced significantly. The primary reason for this switching field reduction is the exchange interaction between the grain boundary and the grain center region. [ABSTRACT FROM AUTHOR]

Noise caused by thermal magnetization fluctuations in giant magnetoresistive sensors, mainly in the free layer, limits the achievable signal-to-noise ratio and thus the density of magnetic recording systems. Here, we describe a quasi-analytical method to study this noise. First, by discretizing the free Layer into sufficiently small rectangular cells, an equilibrium state of the free layer is obtained using a quasi-static energy minimization technique. A linear tensor relation between the magnetization spectra and the thermal fluctuations is found for the two approaches: 1) Landau-Lifshitz-Gilbert-Brown and 2) collective spin wave excitation. In the former, damping and thermal fields are added to each cell and then a Fourier transform is taken to obtain the spectra. For the eigenmode approach, the lossless dynamic equations are diagonalized, yielding the system's intrinsic eigenmodes. Then damping and thermal fluctuations are added to each eigenmode, independently. The sensor playback noise power spectrum density, a measurable quantity, is calculated by sununing up the contributions from each eigenmode or cell magnetization. This computationally light treatment yields a clear physical picture of the phenomenon, relating damping, thermal fluctuation, and noise. We describe each step of the calculation procedure in detail and give examples. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the transition parameter and position jitter in perpendicular media by micromagnetic simulations that included thermal fluctuations. Background on perpendicular recording; Role of thermal fluctuations; Conclusion.

Presents a study that examined the effects of intergranular exchange and anisotropy distributions on signal-to-noise ratio. Details of the proposed tilted perpendicular recording as an effective solution for ultrahigh-density and high-data rate magnetic recording; Role of intergranular exchange and anisotropy distributions;Evaluation of thermal stability.

Presents a study that use error rate analysis to evaluate the effects of surface roughness as well as particle size distributions in a partial-response maximum-likelihood channel. Details of the study; Discussion on the results of the study.

Presents information on a study which developed a three-dimensional micromagnetic perpendicular recording model to analyze high-density perpendicular write fields. Description of the simulation model; Discussion of tapered-neck fields; Dependence of the perpendicular write field on the soft-underlayer thickness.

Presents a study that measured and analyzed signal-dependent noise spectra of metal particle tapes. Background on the use of magnetoresistive heads and fine metal particle tapes in increasing recording densities in modern tape recording systems; Details on the pattern used to eliminate tape speed variations; Analysis of various noise mode contributions for different coating thicknesses.

Part III. Focuses on a study which describes magnetic simulations to examine the effect of intergranular exchange on thermal stability of dibit transitions in magnetic recording, perpendicular media. Analysis on the energy barrier of coupled perpendicular grains; Evaluation of the thermal decay of dibit transitions; Conclusion.

Describes micromagnetic simulations that examine the effect of intergranular exchange on thermal stability of dibit transitions in magnetic recording. Information on the macromagnetic simulation models used; Comparison on the varying magnetic orientation ratios, thermal decays of dibit patterns; Evaluation on the thermal decays of dibit and square wave patterns in perpendicular media.

Part II. Describes micromagnetic simulations to examine the effect of intergranular exchange on thermal stability of dobit transitions in magnetic recording with slightly oriented longitudinal media. Function used for simulating the c axis preferential alignment; Information on the thermal decay of dibit transitions; Conclusion.

Focuses on a study which investigated the potential of extending conventional magnetic recording technology to a one terabit per square inch density using a simple model. Information on the recording simulation procedure; Analysis on the isolated transition and 31-bit pseudorandom sequence; Discussion on the off-track performance.

Presents a study that theoretically examined the playback characteristics of a giant magnetoresistive head for perpendicular recorded magnetization transitions with a soft underlayer. Shape of the isolated signal for different permeabilities of the underlayer; Formulation of an analytical expression for the pulsewidth Tsub[50] and Dsub[50]; Determination of a formula for the transition-noise-limited signal-to-noise ratio.

Describes simulations of servo position error signal (PES) in a perpendicular recording system. Evaluation of the effect of medium noise on the PES detection; Dependence of the servo PES on the average-medium grain in-plane area; Comparison of the PES of longitudinal recording systems with that of perpendicular systems.

Provides information on a study which measured and analyze the fundamental bulk of alternating current and direct current erased tape medium noise utilizing metal particle tapes. Discussion of the particular media noise spectrum; Description of the clustering model and data analysis; Conclusion.

Provides information on a study which examined a system of magnetic grains with resonance interactions. Criterion of resonance interaction; Indirect interaction of grains via antiferromagnetic substrate; Conclusion.

Provides information on a study that investigated the thermal dynamic effects for short write times and long storage times in thin film media. Background on the media for ultra high areal density recording and high data rate; Methodology; Results and discussion.

Focuses on a study which showed the derivation of the three-dimensional fast multipole method (FMM) for use in calculating magnetostatic fields. Discussion of mathematical preliminaries; Description of the FMM algorithm; Performance results for the FMM.

Focuses on a study which used a medium model with random grain structure and desired grain size distribution to examine the effect of medium noise on position error signal (PES) and sensitivity in longitudinal media. Background of the model; Head parameters and simulation process; Comparison among PES detection schemes; Effect of magnetic grain size and grain size distribution.

Focuses on a study which used a magnetic analysis method to determine the mean magnetic spacing of a contact head/tape interface. Background of the magnetic analysis technique; Experimental technique and results; Head/tape spacing obtained from numerical simulations.

Focuses on a study which examined record transitions on a Landau-Lifeschitz-Gilbert model of thin-film recording media. Background of the micromagnetic recording model; Utility o the micromagnetic recording model in the investigation of pole-tip saturation effects for generic head-medium combinations.

Micromagnetic simulations have been performed to compare longitudinal thin film media with and without a grain size distribution. Hysteresis loops and dibit recording are evaluated for various exchange interactions. The results show that the grain size distribution reduces effects of both intergranular exchange and magnetostatic interactions. [ABSTRACT FROM PUBLISHER]

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 σ and roughness correlation length l. The results show that the magnetic recording determination of σ and l agrees extremely well with the mechanical measurements. [ABSTRACT FROM PUBLISHER]

Presents information on a study which proposed a model of signal-to-noise ratio (SNR) that depends on the thermal decay of recorded magnetization in a longitudinal thin-film disk media. Description of the experimental measurement technique of noise decay; Review of the model for calculating magnetization decay; Model for medium noise and SNR; Calculation results of noise power and SNR decay; Experimental comparisons; Conclusions.

Presents information on a study which described a model for error rate analysis including the effect of texture noise. Error rate model for colored noise; Analysis of signal, noise, and the effect of equalization; Results of applying the model to examine various types of partial response channels and replay heads.

Proposes a Guzik 1701 MP Spinstand, an experimental technique for the measurement of time dependence of playback voltage due to the decay of recorded magnetization patterns. Descriptions of the technique; Parameters of the thin film disks; Methods used to conduct the study; Conclusions.

Studies the overwrite in particulate tape media that utilizes a micromagnetic simulation model. System configuration and the three-dimensional micromagnetic simulation model; Overwrite with different system parameters; Overwrite versus the demagnetizing ration in particulate media; Overwrite with different head parameters in the thick tape; Conclusions of the study.

The energy barrier to be overcome for thermal reversal, the reversal mode and the effective particle volume involved are determined by the saddle points of the energy surface. We investigate the influence of field misorientation, exchange-coupling and magnetostatic interaction for a 2:1 aspect ratio particle discretized into two subunits. typically, increasing the field angle from 0° to 45° enhances the effective volume in both cases by more than 20%. [ABSTRACT FROM AUTHOR]

A micromagnetic model for the writing process in perpendicular magnetic recording is developed to study the effect of the soft underlayer on the dynamic reversal of the recording layer. The upper part of the soft material is discretized micromagnetically, each spin following LLG dynamics; the remaining part has infinite permeability. The validity of the model is tested in the static case. Dynamically, high-frequency spin motion is observed in the soft layer. Nevertheless, the field inside the data layer follows the time dependence of the input waveform. [ABSTRACT FROM AUTHOR]

A micromagnetic Monte Carlo simulation is developed to study the thermal decay and erasure process for perpendicular recording media. The switching probability is calculated based on both the energy barrier analysis and the master equation. The results show that for current head media combination at 1 Tb/in², the ensure is severe for the neighboring tracks unless the bit-aspect ratio is increased. The magnetic write width for both side shielded (SS) and no side shield (NSS) head is about the same. The erase band for the SS write head is significantly smaller (20 nm less) than that for the NSS head, corresponding to 10 nm or 12% track pitch reduction. [ABSTRACT FROM AUTHOR]

Presents a study which examined thermal decay of interacting magnetic grains in perpendicular thin film media for magnetic recording. Discussion of thermal-dynamic reversal in coupled grains; Analysis of two nonidentical perpendicular grains; Results.

Presents a study which examined the effect of head field rise time in perpendicular magnetic recording. Development of an analytic recording model; Calculation of the combined image-field from the single-pole writer and the soft underlayer; Importance of image field in the determination of write position and the nonlinear transition shift.

Discusses a study which examined thermal energy barrier distributions in longitudinal recording performing micromagnetic simulations. Description of the micromagnetic simulation model; Overview of the thermal decay model; Results; Conclusion.

Focuses on a study which examined switching speed in perpendicular recording media from micromagnetic simulations, by applying a uniform reversal field to an array of magnetic grains. Description of the model; Effects of applied field strength; Effect of damping constant; Effect of exchange coupling.

Deals with a study that obtained an analytic solution for the distribution of the magnetic orientation of two grains. Importance of understanding the magnetic characteristics of thin film media in the field of magnetic recording devices; Methodology; Results and discussion.

Deals with a study that investigated the effects of three anisotropy sources on the orientation ratio in circumferentially-textured longitudinal recording media. Background on the magnetic anisotropy introduced by the circumferential texturing in cobalt-alloy longitudinal recording media; Methodology; Results and discussion.

Presents a study which analyzed measurements on elongated particles in magnetic tape using a model of reversal field versus pulse time. Description of the model; Results; Discussion; Conclusion.

Provides information on a study which performed micromagnetic simulations to compare longitudinal thin film media with and without a grain size distribution. Effect of grain size distribution on the effect of the exchange interaction; Use of various techniques to generate a non-uniform grain size distribution; Why the same micromagnetic simulation algorithm for the uniform grains can be applied without any modification.

Presents information on a study which presented an analytical formula for calculating the magnetostatic field from a transition with a tanh transition shape. Nonlinear transition shift of a dibit pattern; Optimal precompensation for a series of transitions; Conclusions.

Presents information on a study on the signal to noise ratio scaling and density limit estimates in longitudinal magnetic recording. Analysis; Scaling relations; Conclusion.

Presents information on a study which examines the thermally assisted reversal in noninteracting single domain particles through the use of a micromagnetic model with a stochastic fluctuation field. Presentation of the results of the thermal decay for a single domain particle; Introduction of a set of dimensionless variables; Conclusions.