Magnetic Recording Technology Research Articles

Sperimagnetic states in amorphous Gd x (FeCo)1-x (0.2 ≤ x ≤ 0.3) alloys: insights from stochastic magnetic anisotropy analysis

Materials crucial for the advancement of magnetic recording technologies stand as pivotal elements in the development of a new generation of recording devices. Recent advancements in the manipulation of magnetization through laser pulses have underscored the significance of magnetic materials exhibiting robust magneto-optical properties. This study explores the manifestation of a sperimagnetic state in ferrimagnetic amorphous Gd x (FeCo)1−x alloys utilizing a stochastic magnetic anisotropy approach. Phase diagrams ‘magnetic field’-‘temperature’ and temperature dependencies of magnetization and compensation point were calculated using the mean-field approximation for temperature range from 50 to 700 K and different stoichiometry of the alloy, namely 0.2 ≤ x ≤ 0.3. Accounting for the stochastic anisotropy intrinsic to rare earth ions, a distribution of magnetic moments within the amorphous solid is discerned. Notably, this distribution predominantly manifests at the fringes of a canted phase, constituting the sperimagnetic structure. We demonstrate a direct correlation between an increased variance in normally distributed anisotropy constants of rare earth ions and a corresponding augmentation in the standard deviation of magnetization within the sperimagnetic structure. These findings not only contribute to a deeper understanding of the interplay between material composition and magnetic properties but also provide valuable insights for the advancement of magnetic recording technologies.

Bit-island arrangement and signal processing in double-layer magnetic recording technology

The escalating demand for high-density storage of hard disk drives has prompted the innovation of advanced technologies to significantly boost an areal density (AD). Among these, three-dimensional magnetic recording systems incorporating double recording layers and bit-patterned magnetic recording (BPMR) have currently emerged as one promising solution. Therefore, this article investigates the integration of double-layer magnetic recording and BPMR technologies which is called double-layer BPMR, aiming for a substantial increase in AD. The primary focus lies on minimizing inter-layer interference and mitigating two-dimensional interferences by optimizing bit-island sizes for both upper and lower layers under the incorporation of staggered-like recording media arrangement and an array of magneto-resistive readers. Moreover, we also employ a rate-5/6 modulation code for compensating these effects. Detailed examinations reveal that our proposed system has a superior bit-error rate performance compared with conventional single-layer BPMR system.

Writing temperature and thickness dependence of perpendicular magnetic-dot magnetization reversal probability

Investigation is necessary to figure out magnetization dynamics at high temperatures due to the low power requirement for heat-assisted magnetic recording technology. The Landau-Lifshitz-Gilbert equation was employed to assess the dynamic of magnetization in perpendicular magnetic-dots at elevated temperatures, considering the thermal contribution to the effective field. The simulated perpendicular magnetic-dot has a 50×50 nm2 surface area with thicknesses of 10 nm, 50 nm, and 100 nm. This study reveals that the probability of magnetization reversal and the threshold field in the thermally-assisted magnetic reversal process of a magnetic dot is influenced by the thickness and writing temperature. Below the Curie point, as sample thickness increases, demagnetization energy increases, requiring a larger external magnetic field for magnetization reversal. For the thicker sample, the magnitude of the writing field decreases as the temperature increases, which corresponds to temperature-dependent magnetization. Meanwhile, the optimum writing field is obtained below the Curie point. The magnetic-dot with 100 nm of thickness has an effective writing temperature of 739.7 K with a corresponding writing field is 250 Oe while its reversal probability at zero magnetic field is up to 0.2. Magnetic-dot thickness affects magnetization reversal probability due to domain wall propagation mechanisms during magnetic switching that result from the demagnetization factor. Moreover, as the temperature approaches the Curie temperature, the probability of zero-field magnetization reversal in the absence of an external magnetic field is observed to escalate which has a direct impact on the writing field magnitude. It was found that the effective writing temperature is below the Curie temperature, which allows several hundred Oersted of the writing field.

Recording media configurations for double-layered bit-patterned magnetic recording

The current magnetic recording technology is approaching its recording density limit. Recently, concepts focused on vertically stacking multiple recording media have gained momentum, driven by the potential to significantly expand recording density. The key challenge for such a system involves methods capable of efficiently separating data originating from the upper and lower layers within a single readback signal. To address this challenge, we first propose two distinct configurations of recording media in bit-patterned magnetic recording (BPMR) system with double recording layers. In both configurations, the centers of islands on the lower layer are positioned at the gaps between magnetic islands on the upper layer. This achieves the separation of the individual layer signals since the centers of islands in both layers are deliberately misaligned. Moreover, the equalizer design that takes the input data from both layers into consideration is also proposed. Simulation results demonstrate that when employing the same detector, the proposed configurations of the double-layered BPMR systems achieve better performance than the single-layered BPMR system.

Pulse Electrodeposition of High Moment-High Resistivity Cofex (X=P, O) Alloys and Multilayers for Inductor Application

Growing application of magnetic thin films and inductor chips for analog circuits in mobile phones, MEMS and defense sector technologies rise the need for development of new allows with low energy losses to serve as core material during electromagnetic induction process. Electrodeposition is a cost effective approach to achieve this. The new alloys and their electrodeposition/synthesis process foresee an immediate and direct implementation in future product designs and development and can be easily integrated in an existing manufacturing schemes. The presented work leverages earlier results related to electrochemical synthesis of ferromagnetic alloys. In particular, the work on electrodeposition process for high magnetic moment alloys such as CoNiFe and CoFe i,ii,iii, studies of additive incorporation phenomenon in magnetic alloysi v,v,vi and studies of oxide/hydroxide incorporation in magnetic alloys through the interfacial precipitation process vii,viii,ix. Results will be presented describing synthesis process and bath chemistry for highly resistive CoFeX alloys (X=O and/or P) using electrodeposition process with simultaneous Fe(OH)3 precipitation/incorporation and/or (PO3)3- and (H2PO2)- reduction. Fe-oxide/hydroxide and P inclusions in CoFe matrix serve as resistivity controlling phase in the bulk alloy and as a highly resistive barrier layer in the CoFeX/X laminated structures. The main result is design of a a cost-effective electrodeposition process and solution chemistry yielding the CoFeX alloys in composition range where the maximum possible magnetic moment and permeability is expected (Ms ≈ 2.4 T, μ > 1000). The overall content of the “X” component is designed to yield resistivity above 100 μΩcm. These alloys are tested for high frequency applications and their Snoek limit is identified. The correlation between the CoFeX alloys and CoFeX/X laminates properties and their metallurgical structure is discussed.i) S.R. Brankovic, N. Vasiljevic, and N. Dimitrov. “Applications to magnetic recording and microelectronic technologies.” Modern Electroplating (2010): 573-615.ii) S.R. Brankovic, N. Vasiljevic, T. J. Klemmer, and E. C. Johns. Journal of the Electrochemical Society 152, (2005): C196-C202.iii) S.R. Brankovic, X.M. Yang, T. J. Klemmer, and M. Seigler. IEEE Transactions on Magnetics 42, (2006): 132-139.iv) S.R. Brankovic, R. Haislmaier, and N. Vasiljevic. Electrochemical and Solid-State Letters 10, (2007): D67-D71.v) J. George, J. Rantschler, S. Bae, D. Litvinov, and S.R. Brankovic, Journal of the Electrochemical Society 155, (2008): D589-D594.vi) S.R. Brankovic, Electrochimica Acta 84 (2012): 139-144.vii) S.R. Brankovic, S. Bae, and D. Litvinov, Electrochimica Acta 53, (2008): 5934-5940.viii) J. George, S. Elhalawaty, A. J. Mardinly, R. W. Carpenter, D. Litvinov, and S.R. Brankovic, Electrochimica Acta 110 (2013): 411-417ix) S. Elhalawaty, R. W. Carpenter, J. George, and S. R. Brankovic. Journal of the Electrochemical Society 158, (2011): D641-D646.2011): D641-D646.

Granular micromagnetic HAMR model: investigation of damping dependence and parametric optimization for high performance

Heat assisted magnetic recording (HAMR) is a novel high-density magnetic recording technology that relies on thermal assist from a laser during the writing process. To achieve high writing performance, it is important to study and optimize the crucial factors affecting the magnetization reversal mechanism at elevated temperature. In this work, we use a multiscale approach that combines atomistic and micromagnetic models to study the magnetization reversal behavior in the recording medium. The atomistic model allows to parameterize accurately the macroscopic approach, which is utilized to model the system and its dynamics. We perform a parametric investigation of the switching properties as a function of the HAMR setup characteristics as well as the material properties, such as magnetic damping. The results show that high damping and moderate external fields can achieve high-performance HAMR media characterized by high switching probability, short switching time and low peak temperature. We demonstrate that switching occurs via the linear reversal mechanism. By systematic variation of the longitudinal susceptibility we force a transition to coherent reversal and demonstrate that this reduces the switching probability, showing linear reversal to be an important component within the HAMR process.

Coexistence of tetragonal and cubic phase induced complex magnetic behaviour in CoMn2O4 nanoparticles

CoMn2O4, known for its extensive range of applications, has been subject to limited investigations regarding its structure dependent magnetic properties. Here, we have examined the structure dependent magnetic properties of CoMn2O4 nanoparticles synthesized through a facile coprecipitation technique and are characterized using x-ray diffractometer, x-ray photoelectron spectroscopy (XPS), RAMAN spectroscopy, transmission electron microscopy and magnetic measurements. Rietveld refinement of the x-ray diffraction pattern reveals the coexistence of 91.84% of tetragonal and 8.16% of cubic phase. The cation distribution for tetragonal and cubic phases are (Co0.94Mn0.06)[Co0.06Mn1.94]O4 and (Co0.04Mn0.96)[Co0.96Mn1.04]O4, respectively. While Raman spectra and selected area electron diffraction pattern confirm the spinel structure, both +2 and +3 oxidation states for Co and Mn confirmed by XPS further corroborate the cation distribution. Magnetic measurement shows two magnetic transitions, Tc1 at 165 K and Tc2 at 93 K corresponding to paramagnetic to a lower magnetically ordered ferrimagnetic state followed by a higher magnetically ordered ferrimagnetic state, respectively. While Tc1 is attributed to the cubic phase having inverse spinel structure, Tc2 corresponds to the tetragonal phase with normal spinel. In contrast to general temperature dependent H C observed in ferrimagnetic material, an unusual temperature dependent H C with high spontaneous exchange bias of 2.971 kOe and conventional exchange bias of 3.316 kOe at 50 K are observed. Interestingly, a high vertical magnetization shift (VMS) of 2.5 emu g−1 is observed at 5 K, attributed to the Yafet–Kittel spin structure of Mn3+ in the octahedral site. Such unusual results are discussed on the basis of competition between the non-collinear triangular spin canting configuration of Mn3+ cations of octahedral sites and collinear spins of tetrahedral site. The observed VMS has the potential to revolutionize the future of ultrahigh density magnetic recording technology.

Leveraging Journaling File System for Prompt Secure Deletion on Interlaced Recording Drives

With the growing awareness of secure computation, more and more users want to make their digital footprints securely deleted and irrecoverable after updating or removing files on storage devices. To achieve the effect of secure deletion, overwritten-based secure deletion techniques have been proposed to overwrite invalidated storage space with scrambled data content. Nevertheless, overwritten-based secure deletion requires explicit write requests for rewriting invalidated storage space with random data, thus incurring additional internal write traffic on storage devices. Recently, this inefficient aspect of secure deletion is exacerbated by the emergence of high-density interlaced magnetic recording (IMR) technology. IMR technology enhances the storage density of hard disk drives by interlacing narrower top tracks on wider bottom tracks. Owing to the interlaced track layout, securely erasing invalidated data on bottom tracks interferes with adjacent top tracks and track rewrites are required to preserve valid data on top tracks; thus, overwritten-based secure deletion on IMR drives significantly enlarges the internal write traffic and impairs the secure deletion efficiency. In this paper, instead of directly alleviating the constraint induced by the interlaced track layout, we propose leveraging the interlaced track layout of IMR drives in combination with the journaling data stream of journaling file systems to enable prompt secure data deletion while minimizing the write traffic of secure deletion operations. Experimental results suggest that the performance improvement achieve by the proposed prompt secure deletion (P-SD) strategy is 51.84% on average, when compared with the previous TrackLace approach on IMR drives.

Optical forces in heat-assisted magnetic recording head-disk interface

A main challenge in Heat-Assisted Magnetic Recording technology is the build-up of contaminants called smear on the near field transducer. In this paper, we investigate the role of optical forces originating from the electric field gradient in the formation of smear. First, based on suitable theoretical approximations, we compare this force with air drag and the thermophoretic force in the head-disk interface for two smear nanoparticle shapes. Then, we evaluate the force field’s sensitivity to the relevant parameter space. We find that the smear nanoparticle’s refractive index, shape, and volume significantly impact the optical force. Further, our simulations reveal that the interface conditions, such as spacing and the presence of other contaminants, also influence the magnitude of the force.

A Unified, SNR-Aware SC-LDPC Code Design With Applications to Magnetic Recording

Spatially coupled (SC)-low-density parity-check (LDPC) codes are known to have outstanding error-correction performance and low decoding latency, which make them an excellent choice for high-density magnetic recording (MR) technologies. Whereas previous works on LDPC and SC-LDPC codes mostly take either an asymptotic or a finite-length design approach, we propose a unified framework for jointly optimizing the codes’ thresholds and cycle counts to address both regimes. We focus on circulant-based (CB) SC-LDPC code family as a representative, high-performance exemplar of structured SC-LDPC codes. The framework is based on efficient traversal and pruning of the code search space, building on the fact that the performance of a CB SC-LDPC code depends on some characteristics of the code’s partitioning matrix, which by itself is much smaller than the code’s full parity-check matrix. We then propose an algorithm that traverses all non-equivalent partitioning matrices and outputs a list of codes, each offering an attractive point on the trade-off between asymptotic and finite-length performance. Our simulations show that our framework results in SC-LDPC codes that outperform the state-of-the-art constructions, over both additive white Gaussian noise (AWGN) and partial response (PR) channel models, and that it offers the flexibility to choose low-signal-to-noise ratio (SNR), high-SNR, or in- between SNR region considering system requirements, e.g., that of the MR device.

Large inverse spin Hall effect in BiSb topological insulator for 4 Tb/in2 magnetic recording technology

It is technically challenging to shrink the size of a tunneling magnetoresistance reader to below 20 nm for magnetic recording technology beyond 4 Tb/in2 due to its complex film stack. Recently, we proposed a reader architecture based on the inverse spin Hall effect to resolve those challenges, referred below as spin–orbit torque (SOT) reader, whose structure consists of a SOT layer and a ferromagnetic layer. However, the heavy metal-based SOT reader has small output voltage and low signal-to-noise ratio (SNR) due to the limited spin Hall angle θSH (< 1) of heavy metals. In this Letter, we demonstrate the integration of BiSb topological insulator with strong inverse spin Hall effect into the SOT reader that can significantly improve the output voltage and SNR. First, we theoretically calculate the noises in a 20 × 20 nm2 BiSb-based SOT reader to establish the relationships between SNR and θSH at various bias currents. We then demonstrate proof-of-concept BiSb-based SOT readers using CoFe/MgO/BiSb stack, which show large output voltages up to 15 mV at an input current of 9.4 kA/cm2 at room temperature. We project a giant θSH = 61 for BiSb. Our work demonstrates the potential of BiSb for SOT reader beyond 4 Tb/in2 magnetic recording technology.

Multilayer perceptron-based detection for a coded two-dimensional magnetic recording

Recently, magnetic recording technology has been on the verge of reaching its recording density limit. Two-dimensional (2-D) magnetic recording (TDMR) is expected to be a candidate for next-generation magnetic recording because it provides powerful 2-D signal processing tools that are seamlessly compatible with the current technology. However, the degradation in signal quality due to 2-D interference when increasing the recording density far beyond the limit is inevitable even advanced signal processing tools cannot thoroughly handle such interference. In this work, we introduce two architectures of the multilayer perceptron (MLP)-based detection capable of producing soft information in the form of a log-likelihood ratio (LLR) for a coded TDMR system. This also enables turbo decoding capability to take place in the system, which further enhances the system performance. Such an architecture has two structures explicitly designed to execute before and during turbo decoding with a low-density parity-check code. In the first architecture, we employ triple MLP-based detection to process three readback sequences individually. For another architecture, it is designed to collectively process three readback sequences using just single MLP-based detection. The results show that both architectures of proposed detections outperform the systems using the conventional detection based on the Viterbi algorithm and single MLP-based detection achieves slightly better performance than triple MLP-based detection despite having much less complexity.

Heat-assisted magnetic recording — Micromagnetic modeling of recording media and areal density: A review

Hard disk drives have become the most commonly used mass storage devices because of their low cost and high storage capacity. However, the current perpendicular magnetic recording technology is reaching the physical limit for its areal density capability (ADC) due to superparamagnetism. To accommodate the rapid increase in the volume of digital data produced globally, heat-assisted magnetic recording (HAMR) has been introduced as a next-generation recording technology. In HAMR, a laser locally heats the media to reduce the coercivity, with the information recorded during the cooling process. To investigate the high-temperature magnetization dynamics that occur during this form of recording, computational micromagnetics is a useful tool. This article provides a brief review of micromagnetic modeling for HAMR and summarizes simulation-based studies on HAMR media. A review of these simulation results can serve as a guideline for the prediction of the ADC limit of HAMR.

Micromagnetic Simulation of L10-FePt-Based Transition Jitter of Heat-Assisted Magnetic Recording at Ultrahigh Areal Density.

The areal density of hard disk drives increases every year. Increasing the areal density has limitations. Therefore, heat-assisted magnetic recording (HAMR) technology has been the candidate for increasing the areal density. At ultrahigh areal density, the main problem of the magnetic recording process is noise. Transition jitter is noise that affects the read-back signal. Hence, the performance of the magnetic recording process depends on the transition jitter. In this paper, the transition jitter of L10-FePt-based HAMR technology was simulated at the ultrahigh areal density. The micromagnetic simulation was used in the magnetic recording process. The average grain size was 5.1 nm, and the standard deviation was 0.08 nm. The recording simulation format was five tracks in a medium. It was found that a bit length of 9 nm with a track width of 16.5 nm at the areal density of 4.1 Tb/in2 had the lowest transition jitter average of 1.547 nm. In addition, the transition jitter average decreased when increasing the areal density from 4.1 to 8.9 Tb/in2. It was found that the lowest transition jitter average was 1.270 nm at an 8 nm track width and a 9 nm bit length, which achieved an ultrahigh areal density of 8.9 Tb/in2.

The Secret Arithmetic of Patterns: A General Method for Designing Constrained Codes Based on Lexicographic Indexing

Constrained codes are used to prevent errors from occurring in various data storage and data transmission systems. They can help in increasing the storage density of magnetic storage devices, in managing the lifetime of electronic storage devices, and in increasing the reliability of data transmission over wires. We recently introduced families of lexicographically-ordered constrained (LOCO) codes. These codes achieve capacity with simple encoding and decoding, and they are easy to reconfigure. In this paper, we generalize our work on LOCO codes by presenting a systematic method that guides the code designer to build any constrained code based on lexicographic indexing once the finite set of data patterns to forbid is known. In particular, we connect the set of forbidden patterns directly to the cardinality of the code and to the rule that uncovers the index associated with a codeword. By doing that, we reveal the secret arithmetic of patterns, and make the code design significantly easier. We design optimal (rate-wise) constrained codes for the new two-dimensional magnetic recording (TDMR) technology. We show notable performance gains as a result of solely applying the new codes. Moreover, we show how near-optimal constrained codes be designed and used to further reduce complexity.

Transmission electron microscopy image based micromagnetic simulations for optimizing nanostructure of FePt-X heat-assisted magnetic recording media

The areal density of the heat-assisted magnetic recording (HAMR) technology has a potential to reach 4 Tb/in2. However, the bimodal grain size distribution and structural defects that are unavoidable in actual FePt-X nanogranular media must be minimized for further reduction of a jitter noise. Here we report transmission electron microscopy (TEM) image based micromagnetic simulations of the FePt-X nanogranular media in order to elucidate the role of structural defects such as [200] misalignment and {111} twins on the magnetic properties. Micromagnetic approximation of experimental out-of-plane hysteresis loops allows to evaluate micromagnetic parameters and volume fractions of the defects in MgO(6 nm)/FePt-BN(1 nm)/FePt-(BN,C,SiO2)(7 nm) granular thin films. Synchrotron XRD of the films validated that the structural defects can be accurately evaluated by the proposed approach. The developed TEM image based micromagnetic simulations can directly link nanostructure of the FePt-X media with magnetic properties, boosting not only the optimization of the HAMR media but also a design of magnetic nanomaterials in general.

Magnetic properties and microstructure of FePt (Ag, C) films with MgTiOBN/CrRu underlayer

The (001) textured L10 FePt film is the promising candidate material for coming heat assisted magnetic recording technology. The material of epitaxial intermediate layer for FePt based granular film was considered by the surface energy and lattice mismatch between FePt and MgO-based materials. The (00L) textured FePt (Ag, C)/MgTiOBN/CrRu film was prepared and the MgTiOBN intermediate layer was prior explored in this study. This layer was sputtered by MgTiOBN target at 435 °C and formed the (002) texture on CrRu (002)/glass. The 6–12 nm thick FePt films were finally deposited on MgTiOBN at 470 °C. The FePt (Ag, C) films illustrate high perpendicular magneto- crystalline anisotropy (Ku) (3.85–3.97 × 107 erg/cm3) and out-of-plane coercivity (17.3–20.1 kOe). The lower in-plane magnetization is evidenced by the lower remanence ratio, [Mr(in-plane)/Mr(out-of-plane) ~0.08–0.14]. The saturation magnetization (Ms) of FePt films are around 752–775 emu/cm3 after co-sputtering with 40 vol% (Ag, C) segregants. From cross-sectional transmission electron microscopy image, the FePt shows island-like grains with contact angle between 35 and 67° and the average FePt grains size is around 20 nm estimated from plane view microstructural images. The reason for nonuniform trapezoidal islands is that diffusive C can penetrate and separated the FePt grains but agglomerated again during thin film formation and the lower grains contact angles was due to close surface energy between MgTiOBN and FePt layer. The release of lattice strain energy was formed the misfit dislocation in between FePt/MgTiOBN interface and epitaxial domain match was evidenced in the (111) plane system.

Detection Scheme With Joint Intertrack Interference and Media Noise Mitigations for Heat Assisted Interlaced Magnetic Recording

Heat assisted interlaced magnetic recording (HIMR) is a promising candidate for the next-generation of magnetic recording technology to further increase the area density beyond 1Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Specifically, the high temperature and low temperature tracks are written in an interlaced order to improve the recording performance. However, the inter-track interference (ITI), inter-symbol interference (ISI) and thermal jitters brought by the increased recording density and Curie temperature variations are severe in HIMR, which degrade the bit error rate (BER) performance obviously. In this study, we propose a multitrack detection scheme with joint intertrack interference and media noise mitigations. Here a multi-task neural network (MTNN) is designed to simultaneously predict ITI pattern and residual media noise, then the 2D variable equalizers corresponding to different ITI patterns are implemented and predicted residual media noises are embedded into the branch metrics of modified Bahl-Cocke-Jelinek-Raviv (BCJR) detector to mitigate ITI and whiten media noise. The simulation demonstrates that the proposed MTNN with variable equalizer and modified BCJR detector (MTNN+VE+MB) algorithm mitigates the ITI and media noise effectively. At the channel bit density of 3.10 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , it provides 2.6 dB signal-to-noise ratio (SNR) gain compared to that of conventional 2D fixed equalizer with pattern dependent noise prediction detector (FE+PDNP) for the low temperature (LT) tracks with 4% Curie temperature variance.

Efficient Parallel Decoding Architecture for Cluster Erasure Correcting 2-D LDPC Codes for 2-D Data Storage

Native 2-D low-density parity-check (LDPC) codes provide 2-D burst erasure correction capability and have promising applications in two-dimensional magnetic recording (TDMR) technology. Though carefully constructed rastered 1-D LDPC codes can provide 2-D burst erasure correction, they are not as efficient as 2-D native codes constructed for handling the 2-D span of burst erasures. Our contributions are twofold. First, we propose a new 2-D LDPC code with girth greater than 4 by generating a parity-check tensor through stacking permutation tensors of size $p\times p\times p$ along with the $i,j,k$ -axes. The permutations are achieved through circular shifts on an identity tensor along different coordinate axes in such a way that it provides a burst erasure correction capability of at least $p\times p$ . Second, we propose a fast, efficient, and scalable hardware architecture for a parallel 2-D LDPC decoder based on the proposed code construction for data storage applications. Through efficient indexing of the received messages in an RAM, we propose novel routing mechanisms for messages between the check nodes and variable nodes through a set of two barrel shifters, producing shifts along two axes. Through simulations, we show that the performance of the proposed 2-D LDPC codes matches a 1-D QC-LDPC code, with a sharp waterfall drop of three to four orders of magnitude over ~0.3 dB, for random errors over code sizes of ~32 kbits or equivalently ~ $180\times 180 2$ -D arrays. Furthermore, we prove that the proposed native 2-D LDPC codes outperform their 1-D counterparts in terms of 2-D cluster erasure correction ability. For $p=16$ and code arrays of size $48\times 48$ , we implemented the proposed design architecture on a Kintex-7 KC-705 field-programmable gate array (FPGA) kit, achieving a significantly high worst case throughput of 12.52 Gb/s at a clock frequency of 163 MHz.

Influence of Recorded Pattern on Background Interference impact in Magnetic Recording

This paper discusses the impact of background interference on a recorded pattern for heat-assisted magnetic recording technology (HAMR). Several patterns of the background track were examined, with the log bit error rate and signal to noise ratio measured via a spin-stand tester using HAMR head and media. It was found that the low frequency pattern gave the highest BER and SNR loss due to the strong magnetic field from the adjacent tracks. Similar to its practical use, the PRBS pattern also showed high interference. These observations may be used to support HDD areal density growth.