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The reduction of the transition curvature of written bits in heat-assisted magnetic recording is expected to play an important role for the future areal density increase of hard disk drives. Recently, a write head design with flipped write and return poles was proposed. In this design, a large spatial field gradient of the write head was the key to significantly reduce the transition curvature. In this work, we optimized the write pole of a heat-assisted magnetic recording head in order to produce large field gradients as well as large fields in the region of the heat pulse. This is done by topology optimization. The simulations are performed with dolfin-adjoint. For the maximum field gradients of 8.1 mT/nm, 8.6 mT/nm, and 11.8 mT/nm, locally resolved footprints of an FePt-like hard magnetic recording medium are computed with a coarse-grained Landau-Lifshitz-Bloch model, and the resulting transition curvature is analyzed. Additional simulations with a bilayer structure with a 50 % hard and 50 % soft magnetic material are computed. The results show, that for both recording media, the optimized head design does not lead to any significant improvements in the written track. Thus, we analyze the transition curvature for the optimized write heads theoretically with an effective recording time window model. Moreover, we check how higher field gradients influence the curvature reduction. The results show that a simple optimization of the conventional head design is not sufficient for effective curvature reduction. Instead, new head concepts will be needed to reduce the transition curvature. [ABSTRACT FROM AUTHOR]

This paper proposes a joint read equalization scheme for interlaced magnetic recording (IMR) employing an array of readers, where multi-reader captured waveforms from asynchronously recorded tracks are jointly processed for single or multiple track data retrievals. In the array-reader-based IMR (ARIMR), the inter-track interference (ITI) collected from one reader is not necessarily synchronized to the other readers, especially in the case of a large cross-track separation (CTS) between the readers due to the linear density differentiation between the neighboring tracks. For the efficient mitigation of such asynchronous ITIs, an effective resampling-based joint equalization scheme is proposed in this paper, where multiple readbacks are digitally synchronized for designated target tracks, and joint processing of them suppresses the ITI in the equalized output. Furthermore, the proposed effective synchronization can be applied for joint multi-track retrievals when the CTS of the array reader is closed to the track pitch. For performance evaluations of the proposed joint read equalization scheme, numerical ARIMR channel simulations by the micro-pixelated magnetic channel model are conducted, and a bit error rate performance is evaluated under various configurations. In addition, waveforms captured from a dual-reader hard disk drive are evaluated with the proposed joint read equalization schemes for practical performance measurements of ARIMR. In both evaluations, unfavorable CTS conditions are investigated to account for the dominant skew effect in ARIMR, where the proposed joint equalization scheme enhances the off-track capability performance, especially with the customized configurations of interlaced recording. In overall, ARIMR with joint read equalization shows the potential of an areal density capability gain and a doubling of the data transfer rate over the conventional perpendicular magnetic recording and legacy IMR. [ABSTRACT FROM AUTHOR]

The understanding of measured jitter is improved in three ways. First, it is shown that the measured jitter is not only governed by written-in jitter and the reader resolution along the cross-track direction but by remanence noise in the vicinity of transitions and the down-track reader resolution as well. Second, a novel data analysis scheme is introduced that allows for an unambiguous separation of these two contributions. Third, based on data analyses involving the first two learnings and micro-magnetic simulations, we identify and explain the root causes for variations of jitter with write current (WC) (write field), WC overshoot amplitude (write-field rise time), and linear disk velocity measured for heat-assisted magnetic recording. [ABSTRACT FROM AUTHOR]

We have studied the impact of structural randomness on the variation in optical absorption of recording grains. Using finite-difference time-domain simulation, we demonstrate that randomness in size, shape, and position of FePt grain can cause 2%–9% variation in absorption, depending on the strength of randomness. We have also discussed the resulting impact of several design parameters: air gap, average grain size and its standard deviation, size, and permittivity of grain boundaries, seedlayer thickness, and aspect ratio of recording grains. We demonstrate that the impact of random absorption on jitter is comparable to experimentally estimated variations in Curie temperature ${\sigma }_{T_{c}}$. In the case of standard recording system parameters, we observe ${\sigma }_{T}\sim 1.5$ % averaged over the write bubble which corresponds to ${\sigma }_{T}\sim 3$ % for the grains inside. [ABSTRACT FROM AUTHOR]

Although significant progress has been made toward achieving 10 Tbpsi and beyond, the continued progression of the hard-disk drive development remains a challenging endeavor. A panoptic view indicates several factors that contribute to the challenge, including media as well as recording head design challenges. The heat-assisted magnetic recording (HAMR) head, specifically, has the broad responsibility of producing a magnetic field, delivering light to the optical transducer, and transforming optical energy into localized thermal energy within the media. Resulting thermal gradients in the recording layer exceeding 10 K/nm can often yield a satisfactory recording performance; however, this can be at the expense of elevated temperatures in the system. Here, we discuss an analysis of a write pole-embedded near-field transducer and demonstrate that it can not only provide improved optical efficiency and cooling in the head but also has the potential to achieve competitive thermal gradients in the recording layer, exceeding 20 K/nm, with peak temperatures 750 K < T < 850 K. Moreover, the best case among the parameter space explored here demonstrates the HAMR recording signal-to-noise ratio levels exceeding 22.5 dB at 1000 kFCI. The results of the analysis strongly suggest that a magnetic write pole-embedded transducer potentially may provide an attractive path toward higher linear densities with the HAMR technology. [ABSTRACT FROM AUTHOR]

Micromagnetic model simulations were performed to investigate spin–torque oscillators (STOs) integrated into the main pole–trailing shield (MP–TS) gap of the write head (integrated STO). First, the oscillation states of a tilted STO were investigated in a model comprising the write head, STO, and medium soft underlayer (SUL). We found that inserting the STO into a non-parallel MP–TS gap resulted in more stable oscillation. Second, we performed full micromagnetic simulations of the write head, STO, SUL, and recording layer (RL), and the oscillation of the tilted STO was investigated. We found that the RL affected the STO oscillation to some extent; however, the effect was smaller than that from the write head. We also discuss the calculation times for various structures with and without the RL, and with/without medium motion. [ABSTRACT FROM AUTHOR]

Differences between heat-assisted magnetic recording (HAMR) and conventional perpendicular magnetic recording at narrow track widths are compared. We can see that HAMR appears to have similar adjacent track interference, but increased readback signal from the adjacent tracks (side reading). This background interference signal appears to be a consequence of the media architecture, and can be decreased if the media soft underlayer spacing to the hard layer, and transducer is reduced. The impact is also reduced for very high linear densities, due to a smaller fraction of unbiased flux from the neighbor tracks reaching the test track. The use of two reader multiple sensor magnetic recording at high track density appears to address some of this issue, and we can demonstrate viable track writing for HAMR beyond 1M tracks per inch using this readback technique. [ABSTRACT FROM AUTHOR]

The spacing between the flying head and the rapidly rotating disk in hard disk drives continues to decrease in order to grow the areal density. In heat-assisted magnetic recording (HAMR), the spacing control complexity is compounded by the additional protrusion resulting from the laser heating. Compared to the writer induced and thermal fly-height control protrusion, the near-field transducer (NFT) protrusion is a faster and more local protrusion that requires new HAMR-specific spacing control techniques. In this paper, we will review the simulation and experimental studies which shed light on both the steady-state and transient characteristics of the NFT protrusion. Simulation analysis reveals the scale of the protrusion and its effects on spacing control. Experimentally, we have demonstrated a novel technique to characterize the NFT protrusion and assist in setting the spacing for each HAMR head. Based upon the knowledge gleaned from characterization, compensation schemes have been developed. Some of the schemes have already been successfully demonstrated. [ABSTRACT FROM AUTHOR]

Microwave-assisted magnetic recording with a tilted spin-torque oscillator (STO) was examined. Tilting the STO toward the trailing shield of a write head makes it easier to achieve stable oscillation. The signal-to-noise ratio (SNR) of written tracks was examined using an analytical head field distribution based on a finite-element model of a write head. The maximum SNR was similar for a range of STO tilt angles, but the optimum position of the STO in the write head gap depended on the STO tilt angle. [ABSTRACT FROM AUTHOR]

A shielded planar head with a multi-step-tapered main pole assuming ion-beam milling fabrication was studied to obtain a large recording field along with suppressed fringing field. The head main pole with a three-step-tapered structure was optimized in terms of the top, main, and bottom slope angles. The optimized head showed a remarkably suppressed fringing field compared with a conventional single-step-tapered pole head. The recording simulation suggests that the head has the potential for 2 Tbit/in2 recording in combination with a bit patterned medium. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is the next generation hard disk drive technology that enables continued and significant areal density growth. There are currently two common architectures for the layout of tracks in hard disk drives: conventional magnetic recording (CMR) and shingled magnetic recording (SMR). In CMR, any track can be written at any time and neighboring tracks do not intentionally overlap. In SMR, the tracks are written sequentially in bands with the tracks intentionally overlapping like shingles on a roof. In this paper, we introduce a novel track layout, interlaced magnetic recording (IMR), and apply it to a HAMR recording system. With heat-assisted IMR, we observed a 31% increase in areal density over HAMR CMR whereas in a HAMR SMR architecture, we observed a 27% increase in areal density over HAMR CMR. [ABSTRACT FROM PUBLISHER]

A prototype perpendicularly oriented sputtered tape sample was investigated using a prototype high-moment tape write head and a 48 nm-wide tunneling magnetoresistive hard disk drive read head. A linear density of 818 kbpi with a post-detection byte-error rate <0.023 was demonstrated based on measured recording data and a software read channel that used an extended version of the noise-predictive maximum-likelihood detection scheme that tracks the mean of the data-dependent noise. Using a previously reported iterative decoding architecture, a user bit-error rate of <1e–20 can be achieved at this operating point. Track-following servo performance characterized by the standard deviation of the position error signal ( $\sigma $ -PES) ≤ 6.5 nm was also demonstrated over a tape speed range of 1.2–4.1 m/s. This magnitude of PES in combination with a 48 nm-wide reader enables reliable recording at a track width of 103 nm corresponding to a track density of 246.2 ktpi, for an equivalent areal density of 201.4 Gb/in2. [ABSTRACT FROM PUBLISHER]

Heat-assisted magnetic recording (HAMR) is the next-generation technology that is required to deliver areal densities in excess of 2 terabit/in2 for high-capacity, low-cost hard drives.The recording process relies on spatially and temporally localized heating of the media surface to lower its coercivity during the magnetic writing process. This scheme drives substantial changes to the recording head write element architecture, combining the conventional electromagnet structure with integrated optical light delivery layers, focusing optics, and plasmonic nanostructures to generate subwavelength optical spots. Power losses associated with the strong optical fields required for heating the media can cause local temperatures in excess of 400°C at the recording head surface. Coupled with high pressures, an oxidative/corrosive air-bearing environment, and a sub-3 nm head-media spacing, this introduces new challenges for the functional materials in recording heads required to balance performance and long-term reliability demands. Here, we briefly review specific challenges associated with HAMR heads, highlighting the major requirements, failure modes, and needed innovations for the near-field transducer and optical-waveguide subsystems. [ABSTRACT FROM PUBLISHER]

One detrimental by-product of heat-assisted magnetic recording writing is the creation of head contamination. Here, we present the current understanding of the driving forces, growth mechanisms, and growth rates of write-induced head contamination. The combination of an evaporation and condensation model with shear forces suggests a flow of lubricant on the head may precipitate contamination. The contamination is observed to grow in the head–media gap until it contacts the media surface, at which point an additional material pickup mechanism can be activated. Evidence of contact-induced transfer and a chemical reaction of the contamination is presented, and the impacts of contamination on head temperatures and thermal gradient is presented. Depending on the contamination properties, head temperatures may be increased substantially, leading to increased reliability risk. Consistent with previous analyses, we find that contamination may increase media thermal gradient. [ABSTRACT FROM AUTHOR]

Resulting from the curved thermal profile by near-field transducers, the transition curvature in heat-assisted magnetic recording is one of the critical factors significantly limiting the technology from achieving expected high area density capability. In this paper, we present a systematic micromagnetic modeling study to understand the underlying physics and to arrive at a solution that can correct the transition curvature for enhancing recording performance. Analysis show that the straightened transitions of the recording with the solution can yield a linear density increase of 50% at the same high track densities. [ABSTRACT FROM AUTHOR]

Simulations of recording on media with two and three distinct recording layers are presented. A high frequency field is used to select the layer on which data are recorded. Layer-selective recording was confirmed for two layer granular media with narrow distributions. For three layer media magnetostatic interactions between the layers led to a loss of selectivity in the bottom recording layer. Readout of data is possible by staggering transitions in different layers or by using a spin-torque oscillator. [ABSTRACT FROM AUTHOR]

The areal density capability (ADC) of a magnetic recording disk drive is highly dependent on the application or market segment. In this paper, we define a new areal density metric, which represents what areal density is possible under ideal recording conditions. This proposed areal density metric enables the industry to standardize and compare the ADC of magnetic recording disk drives across various recording technologies independent of market segment. We demonstrate the performance of experimental 2-D magnetic recording and heat assisted magnetic recording technology components measured using the proposed areal density metric. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic recording (TDMR) offers the opportunity to provide areal density (AD) gain, but questions were unanswered as to how the gain is achieved and what can be done to maximize the gain from this new technology. In this paper, we offer some reasons why different investigators might report different AD gain opportunities. We present data collected on a spin stand with two reader heads and processed with a commercially available field programmable gate array TDMR channel. The implications of this paper should provide guidelines on reader geometries, placement, and performance. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is the next-generation hard disk drive technology which enables continued and significant areal density growth. There are currently three write architectures for the layout of tracks in hard disk drives: conventional magnetic recording (CMR), shingled magnetic recording (SMR), and interlaced magnetic recording (IMR). The read-back architecture multiple-sensor magnetic recording (MSMR) can be combined with the three different write architectures to increase the areal density by using two or more readers to read-back the same track. In this paper, we compare the areal density capability of HAMR CMR, HAMR SMR, and HAMR IMR combined with read-back with one reader, MSMR with two readers, and MSMR with three readers. [ABSTRACT FROM AUTHOR]

The exceeding temperature at Near Field Transducer (NFT) is a mandatory issue in Heat Assist Magnetic Recording (HAMR). It significantly affects both system performance and lifetime. We believe that light reflection off the recording medium could contribute to the temperature rise in the NFT. In this paper, we study light behavior from the NFT output to the media in terms of powers, using 3-D simulation. We found that the light reflection off the recording layer has certain effects on media absorption rate and NFT coupling efficiency. An increase in the NFT temperature is partly induced by the reflected light. When the surface roughness is included, the reflected power to the NFT obviously decreases. The average absorption rate is reduced more than 50%. The maximum absorption rate and smallest coupling efficiency occurs at the roughness Ra = 0.55 nm. [ABSTRACT FROM AUTHOR]

Recording experiments and decoding algorithms are presented for evaluating the bit error rate (BER) of state-of-the-art magnetic bit-patterned media (BPM). The recording experiments are performed with a static tester and conventional hard-disk drive heads. As the reader dimensions are larger than the bit dimensions in both the down-track and the cross-track directions, a 2-D bit-decoding algorithm is required. Two such algorithms are presented in detail together with the methodology implemented to accurately retrieve island positions during recording. Using these techniques, a 1.6 Td/in2 magnetic BPM is demonstrated to support 2-D BER below 1e-2 under shingled magnetic recording conditions. [ABSTRACT FROM AUTHOR]

A 2-D asymmetrical magnetic head is characterized by the parallel inclination of the semi-infinite, inner gap walls, and where the gap length and head-to-underlayer separation are small compared with the other dimensions in the head. With head corner inclination, these structures contribute to the reduction in the effective gap length of the head and, therefore, the increase in the field magnitude and narrowing of the field distributions near the acute gap corner. Asymmetrical heads were, therefore, proposed for increasing the writing and readout resolutions in gapped magnetic head structures. There are currently no explicit or approximate analytical solutions for the potential and fields from 2-D asymmetrical magnetic heads. This paper is concerned with the detailed theoretical derivation of relatively simple closed-form approximations for the scalar magnetic potential and fields from 2-D asymmetrical magnetic heads and their Fourier transforms, applicable to any arbitrary corner inclination angle. A general theory based on the translated sine Fourier series is developed to model and study the reaction of a soft magnetic underlayer on the surface potential of any magnetic head structure, and applied to the asymmetrical head. The approximate potential and field expressions derived in this paper demonstrated a very good agreement with the finite-element calculations of the 2-D asymmetrical heads. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) has been proposed to achieve >1~Tb/in^2 magnetic recording density. In HAMR systems, a laser is used to locally heat the magnetic disk to the Curie temperature, which is \sim400^\circC–600^\circC, to assist in the data writing process. The high temperature working condition is a great challenge for the head-disk interface. Lubricant can be depleted by evaporation or decomposition. The protective carbon overcoat can be graphitized and oxidized. The surface quality, such as its roughness, can be changed as well. The near field transducer (NFT) structure is also vulnerable under the large number of heating cycles. All of those effects of the heating will present challenges for the reliability of the HAMR performance. In this paper, an experimental HAMR platform is introduced. The free space laser exposure of the media is calibrated based on the magnetization decay of special data tracks. Lubricant loss is determined from the optical surface analyzer. The lubricant changes as a function of different thermal load cycles are investigated as well. The disk topography is measured by an atomic force microscope after the mobile lubricant is removed. The hard overcoat's topography dependence on the laser exposure conditions is also studied. With regard to the media disk, we establish three distinct laser power thresholds for lubricant loss, disk surface degradation, and magnetization decay. As the laser power increases, the lubricant starts to change first before the magnetization starts to decay, indicating that lubricant could be the most vulnerable component to the laser heating in HAMR systems. Then, the disk overcoat's surface changes, becoming rougher after the magnetization starts to decay. Furthermore, the lubricant degradation is more serious under cyclic loading conditions. With regard to the transducer, the metal film of the NFT gets removed due to high energy laser ablation, and then the NFT loses its capability to focus the light, as required for HAMR systems. [ABSTRACT FROM PUBLISHER]

The use of a wider writing shingled magnetic recording (SMR) head in spinstand experiments allowed different regions of the SMR track to be analyzed and described. Here, we break the track into curved, best, and trimmed areas. The curved area is written with the writer edge, which has high curvature and poor write field gradient, resulting in low resolution and high noise. The trimmed region is defined by head fields combining with disk demagnetization fields. Together these fields attack the low frequency magnets, boosting resolution, increasing noise, and generating a narrow out of phase copy of the trimmed track (the negative sliver). This is explained via measurements and modeling. We also explain the measured magnetic write width dependence on linear density based on the frequency response of the reader as well as writer and media effects. We employ linear deconvolution to extract the binary impulse responses of the SMR data track and its neighboring tracks to characterize intertrack interference. The writer and media effects, which give rise to the negative sliver observed, are shown to explain the interference behavior with linear density. [ABSTRACT FROM PUBLISHER]

Heat-assisted magnetic recording (HAMR) is a fast evolving technology, and has been established as the next enabler of higher areal density in magnetic recording. After achieving high areal density capability, HAMR drive integration was recently demonstrated. In this paper, we discuss some of the recent learning from component performance and drive integration. We identify a key challenge in HAMR integration: erasure due to thermal background heating. The background heating was introduced to improve near-field transducer reliability and reduce laser power requirement. We present experimental and modeling data on the impact of thermal background, both in the cross-track (adjacent-track erasure) and down-track (self-erasure) dimensions. [ABSTRACT FROM PUBLISHER]

The formation of defects on a magnetic recording disk is one of the critical issues in the reliability of a hard disk drive. When a magnetic recording head comes into contact with a disk defect, the resulting surface damage can cause significant degradation on read/write performance. Considering the carbon atoms in diamond like carbon (DLC) coating can experience phase change and oxidation under high temperature (i.e., mechanical softening process due to the thermal stability), the frictional heat generated by the sliding contact between a head slider and a disk defect can lead to severe damage on the head DLC film. In addition to the mechanical degradation of the head DLC film, the magnetic properties of underlying read/write elements and shield materials can also be deteriorated due to the mechanical stress and high temperature rise. In this paper, the thermomechanical contact between a head slider and a disk defect was systematically examined through analytical modeling and simulations. For the three different disk defects (i.e., Al2O3, SiO2, and AlTiC), the temperature rise and distribution on the contact area were determined from a theory of contact mechanics and heat transfer with the modified Francis heat partition factor. To obtain more physical insight into the thermomechanical head disk contact, parametric study was performed using a modified control parameter (\psi^\ast), which was made of material properties of a disk defect and system operating conditions. According to the simulation results, it was observed that Al2O3 showed the worst thermomechanical contact performance among the three defects as it generated the highest flash temperature of 439.0^\circC on the head DLC film. The increased surface temperature was high enough to degrade the head DLC film as well as the underlying magnetic materials. Moreover, it was found that the surface temperature rise on a head slider was proportional to the values of \psi^\ast. [ABSTRACT FROM PUBLISHER]

With the distinct advantage of retaining conventional head and media, the emerging shingled recording technology improves areal storage density through intentional track overlapping that nevertheless introduces severe intertrack interference (ITI). An economically tenable option for shingled drives is to utilize a single read head. As we continue to increase its areal storage density, there will be a higher probability that a read operation demands reading multiple adjacent tracks for explicit ITI compensation. This directly results in a significant read latency penalty when using a single read head. In this work, we propose a simple design strategy to reduce such ITI-induced read latency penalty. If a sector of user data can be compressed to a certain extent, it will leave more storage space for coding redundancy and, hence, opportunistically enable the use of a stronger-than-normal error correction code (ECC). The stronger ECC can accordingly reduce the probability of reading multiple adjacent tracks for explicit ITI compensation. Beyond a simple intrasector compression, the absence of the update-in-place feature in shingled recording makes it feasible to apply lossless compression across multiple consecutive sectors. This can further improve the compression efficiency and, hence, reduce the probability of reading multiple adjacent tracks. We carried out simulations that successfully demonstrate the effectiveness of the proposed design strategies on reducing the read latency penalty caused by severe ITI in shingled recording. [ABSTRACT FROM PUBLISHER]

A method from near-field optics to thermal analysis is developed for the heat-assisted magnetic recording (HAMR) head and media. The distributions of power absorptions in the system of the HAMR head and media are simulated with finite-difference time-domain (FDTD), which is coupled with transiently thermal conduction equation for thermal analysis. The study focuses on the influence of the writer pole on the efficiency of transducer and thermal performance of the HAMR head and media. The results show that the efficiency of transducer largely reduces from 3.36% to 0.55% due to the power absorption of the writer poles. However, the writer pole plays a role of thermal sink bar so that the temperature of transducer also reduces largely. The distance between the transducer and writer pole strongly affects the efficiency of transducer, temperatures of media, transducer and writer pole. It is found that without the thermal sink role of the writer pole, the temperature of transducer is very high when the media temperature is required to reach the Curie temperature of FePt media. Two shapes of the writer poles including rectangle and step-down shapes have been used for the efficiency and thermal analysis. Their size effects on efficiency and temperatures are also studied. [ABSTRACT FROM AUTHOR]

Heat assisted magnetic recording (HAMR) is anticipated to increase the areal density in hard disk drives to multiple Tb/in^2. However, the newly introduced protrusions caused by additional heat sources must be taken into account in head-disk spacing control. The light absorption by the near field transducer (NFT) and the heat dissipation into the slider through the laser delivery system can result in the temperature rise well over a hundred degrees Celsius. In response to such a big temperature change, an instantaneous protrusion at the NFT region is expected. This protrusion has a direct impact on the head-magnetic spacing (HMS) and therefore affects writing performance. Due to its small lateral size below 1 micrometer, the NFT protrusion is difficult to probe. In this paper, we introduce a new technique, which is based on atomic force microscopy (AFM) and allows for a simultaneous topography imaging and NFT protrusion mapping on the air bearing surface (ABS) with a nano-scale resolution. The measured NFT protrusion profile of a nonflying head indicates the local min-fly point at the location predicted by our simulation results. A further quantitative analysis proves the dependence of NFT protrusion on the laser power, which agrees very well with modeling and can offer a good guidance to the head-disk interface management during recording. [ABSTRACT FROM AUTHOR]

In thermally assisted magnetic recording, one of the most important issues is the reliability of the near-field transducer and the magnetic recording head. When the near-field transducer transfers the optical energy to the media through coupling from the waveguide, it inevitably heats itself and its surrounding area, such as the magnetic recording head, which tends to cause long-term performance degradation. To mitigate the problem, one possible solution is to apply a pulsed laser beam instead of a constant one. In this paper, the performance characteristics of the pulsed thermally assisted magnetic recording are analyzed by modeling. Simulation results show that similar recording performance can be achieved through a much reduced laser beam duty cycle (\sim30%). [ABSTRACT FROM AUTHOR]

Bit patterned media (BPM) provide an alternative to conventional granular thin film recording media, circumventing the challenges of managing grain size and its associated noise and thermal stability issues in granular media. A viable fabrication strategy involves creation of a master pattern by rotary-stage e-beam lithography and directed self-assembly of block copolymers, followed by pattern replication via UV-cure nanoimprint lithography and pattern transfer to a magnetic thin film by ion beam etching. These steps have been demonstrated for 150 Gdot/cm^2 (1 Tdot/in^2) hcp patterns, achieving a dot placement tolerance of 1.2 nm 1\sigma and a defect rate of <10^-3. Media samples fabricated in this manner from continuous CoCrPt alloy films have achieved a 1\sigma switching field distribution of 4% of \mbi H\mmb c. A 2T medium SNR of nearly 14 dB and a write bit error rate of 2\,\times\,10^-3 have been shown using a static tester with a conventional product read/write head. Modeling and experiment suggest that higher recording density can be achieved using BPM with a bit aspect ratio (BAR) > 1. A master pattern generation generation strategy for BAR > 1 with rectangular islands is shown using intersecting lines generated by directed self-assembly of lamellar block copolymers in combination with spacer-defined line doubling. [ABSTRACT FROM AUTHOR]

A shingled recording head design is proposed that makes use of a saturation magnetization gradient to focus flux into the corner of the writing pole. This design yields field gradients of 800 Oe/nm and can write more than 2.5 \Tbits/in^2 of user data onto a 10 nm thick ECC recording layer with 6 nm Voronoi grains. Maximum user densities are predicted to be over 4.66 \Tbits/in^2 with 8 nm grains and 12 \ \Tbits/in^2 with 5 nm grains using a perfect read and write scheme at a 1:1 bit aspect ratio. For read back, three contact dual differential MR head designs that have two independent free layers with magnetization pointing oppositely are examined for the purpose of extending magnetoresistive technology. The differential head shows good cross track resolution that will be advantageous at the low bit aspect ratios likely for two-dimensional magnetic recording. Results show that an array of three dual differential heads can successfully resolve an 8 nm track surrounded by adjacent tracks that have pseudo random bit sequences written to them, even though each head is wider than the track. [ABSTRACT FROM AUTHOR]

Magnetization switching in energy assisted recording is examined using micromagnetic simulations. Heat assisted and microwave assisted recording are compared. The high frequency magnetic field used in microwave assisted recording can be used to reduce the switching field or the switching time, but the optimum frequencies have opposite trends as a function of temperature. In heat assisted recording the switching times at temperatures near to the Curie temperature are about half the room temperature value. In recording simulations heat assisted recording was able to write the highest quality tracks and has the potential to be able to write on media with much higher anisotropy than microwave assisted recording. [ABSTRACT FROM AUTHOR]

Bit patterned media recording (BPMR) is a candidate technology proposed to extend the areal density growth capability of magnetic recording systems. In conventional granular magnetic recording (CGMR), bits of information are recorded onto a number of randomly distributed magnetic grains. The difficulty for the granular media approach is that due to the randomness of the grains, a certain minimum number of grains are required in order to maintain the media signal to noise ratio (SNR). This requires smaller grains as the bits are shrunk and we end up with either unstable, or unwriteable grains as per the well-known media-trilemma. In BPMR, instead of random positions, the ``grains'' are ordered into a well-defined lattice of magnetic islands. Because of this ordering, the media SNR is no longer determined by the number of grains per bit as in CGMR, but is defined by the geometrical and magnetic distributions of the fabrication process of the media. Analytical models exist for BPMR, that flip grains in the media based on the switching field distribution (SFD) and the knowledge of the applied head field. On the other side, a statistical model for CGMR has been proposed that measures probabilities of grains flipping based on micromagnetic simulations, named the grain flipping probability (GFP) model. In this work, we adapt the GFP model for BPMR and perform a comparison between densities predicted via the analytical and GFP models, by processing the signals from these models with the appropriate detectors and LDPC (low density parity check) decoders. [ABSTRACT FROM AUTHOR]

The thermal flying height (FH) control technology had been applied to adjust FH in hard disk drive (HDD) during read/write processes. The readback signal-based in-situ FH testing technology is the feasible way to monitor and control the FH of heads in HDD. For perpendicular recording, the soft magnetic underlayer has the effects on readback signal and change the Wallace equation into a hyperbolic formula with no explicit solution to the spacing change versus the signal amplitude. Fortunately, the hyperbolic formula can be reduced to the traditional Wallace spacing loss equation at short wavelength. In the actual application, there is a need to compare the FH change or modulation at different disk locations and the harmonic ratio method is preferred to cancel media magnetic fluctuations and a certain level of off-track. This work proposed a new code pattern (11110000) to generate three major harmonic signals: the first, the third, and the fourth harmonics. With zero of the second harmonic signal, the harmonic energies are able to concentrate to the third and the fourth harmonics with strong signal intensity. The most important feature is that both the third and the fourth harmonics can meet the short wavelength requirement with enough signal intensity. This allows the new triple harmonic method to measure FH by the ratio of the fourth over the third harmonics. With the both harmonics in the range of short wavelength, it guarantees the accuracy of FH measurement during the touchdown process. [ABSTRACT FROM AUTHOR]

At 10 \Tb/in^2 areal density and bit aspect ratio (BAR) of 4, the 1 T bit length is only 4 nm. By proportional scaling, it requires the head media spacing (HMS) to be around 2 nm. In such a small spacing, it is extremely hard to squeeze in the medium overcoat and lubricant for having a reliable head disk interface. This small HMS demand is mainly determined by the readback process for the reader to have large signal intensity and high signal resolution. The differential dual spin valve (DDSV) reader incorporates a metallic gap layer between the free layers of two spin valves. The opposite pinned reference layers generate the differential operation and reproduce the pulse signal from the transition of perpendicular magnetizations. With the readback resolution defined by the thicknesses of gap layer and two free layers, the DDSV reader gains more resolution than the conventional reader. Unlike conventional reader also using two shields to define signal resolution, the shields of DDSV reader is only for the elimination of inter-symbol interference. This allows the shield to shield spacing of DDSV reader to be much larger, which has smaller shunting effect and promotes the signal strength. With stronger signal intensity and higher readback resolution, the DDSV reader is able to reproduce good quality signal at much higher HMS than the conventional reader. [ABSTRACT FROM AUTHOR]

Lateral motion of the magnetic tape in data storage applications misaligns the flexible medium relative to the recording head and reduces the potential for decreasing data track width and spacing, and thereby the achievable data storage density. In order to reduce the effect of misalignment between the tape and the recording head, the head is mounted on a track-following actuator that can compensate for the position error up to a frequency that is governed partly by its mechanical resonances; this bandwidth is typically 1 kHz or less for conventional voice coil-based actuators. This paper introduces the design and implementation of a track-following actuator that is piezo-electrically actuated in order to potentially achieve a significant increase of bandwidth and positioning precision. A proof-of-concept is prototyped and experimental results are presented. An H\infty controller is designed and implemented to compensate for typical disturbances such as periodic runout of packs and rollers, or non-periodic flange impacts. Preliminary closed loop experimental results with an experimental low lateral motion tape path, and conventional servo format and media demonstrate a reduction in positioning error standard deviation to 74.5 nm, with simulations indicating a potential for further improvement to 20.6 nm with the use of improved media and servo format. [ABSTRACT FROM AUTHOR]

In this paper, a thermally assisted magnetic recording (TAMR) head gimbal assembly (HGA) with an optical fiber and prism is proposed. The stiffness of a TAMR HGA is increased by an optical fiber and prism. Therefore, in this paper, operating shock analysis of a TAMR HGA considering the thermal effects during writing to record the data is numerically performed. Flying height (FH) analysis considering the thermal deformation by laser source also is investigated. As a result, judging from shock point of view, the shock characteristic of a TAMR HGA is better than that of conventional HGA. However, when considering the thermal effects during writing to record the data, the risk of contact for a TAMR HGA between media and slider is larger than that of conventional HGA. Hence, to solve these problems of a TAMR HGA, we should consider selection for material of media and TAMR slider, and design for head parts of TAMR slider. [ABSTRACT FROM AUTHOR]

A static drag tester was developed for characterization and read/write of patterned and continuous magnetic disk media. To enable write synchronization for patterned media application, a scheme for write synchronization was designed and implemented. The results for synchronized writing of patterned bits using a read-while-write approach are presented and they indicate that read-while-write is a viable approach for flexible written-in error tests at drag tester level. Besides application for pattern media, a method suitable for study of energy assisted media by drag tester was also explored. The results show that the required switching field reduced as the temperature of the recording medium was increased. The drag tester is thus shown to be a flexible and valuable platform for the study of future magnetic recording media. [ABSTRACT FROM AUTHOR]

Abstract: Bit-patterned media are being considered as a promising approach for achieving multi-terabit per inch recording densities. The effects of different recording density of bit-patterned media of mechanical surface loading on deformation of elastic-plastic multi-layers are analyzed by using the finite element method. The thermal protrusion of a thermal flying height control (TFC) slider and the wave surface of an elastic-plastic thin film are chosen to perform a contact analysis at the head-disk interface (HDI). A two dimensional finite element model between head and patterned media is then developed. Two patterned media cases are investigated and presented in this paper. The evolution of deformation in multi-layer media due to mechanical surface loading is presented by maximum von Mises stress and contact pressure. [Copyright &y& Elsevier]

We have studied the recording process of an obliquely evaporated Co-CoO medium. The experimental readback waveforms and the spin-SEM images of the recorded magnetization reveal an interesting magnetization process upon increasing the write current in one of the two recording directions. With larger write currents, isolated readback pulses drastically change their shape and the remanent magnetization of the written domains decreases. We qualitatively reproduce this behavior using simple write models that include the three-dimensional (3-D) granular nature of the medium and a distribution of anisotropy axes for the evaporated Co grains. Based on these results, we propose a recording scheme in which a patterned multilevel tilted recording medium is used advantageously for 3-D magnetic recording. [ABSTRACT FROM AUTHOR]

Due to continuous increase in areal density, the head-media spacing combining head & media overcoat, lubricant film and fly height, is expected to be less than 6.5 nm for 1 Tbits/in² hard disk drives (HDDs). The intermittent contacts between head and disk during operation are unavoidable and cause lubricant depletion in the film. Therefore, the nanoscale conformation and self-healing ability (i.e., spreading) of perfluoropolyether (PFPE) lubricant nano films is critically important in the head-disk interface to maintain long-term reliability of HDDs. In this paper, the spreading phenomena for pure and binary mixture PFPE lubricant nano films on the carbon-overcoated media were examined via molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effect of read head profile on the playback signal from data and servo sector in a staggered bit-patterned-media recording system. The scaling of the read head is targeted to achieve better data signal quality while such scaling is shown to have negative effect on the servo signal. A secondary servo burst that uses data samples to generate supplementary PES is then proposed and its feasibility is demonstrated. [ABSTRACT FROM AUTHOR]

A systematic experimental study of reverse overwrite (ReOVW) process in the shingled recording scheme has been conducted in conjunction with characterization of corresponding recording performances from recording heads with different geometries. It was found that not only is there no ReOVW reduction as the track density increases, but also ReOVW is, in fact, slightly increased from 300 ktpi to 600 kpi or beyond by using the same writing conditions. These data suggest that conventional magnetic recording technology might be able to extend all the way beyond an areal density of one Tbit/in² by using the shingled recording scheme. [ABSTRACT FROM AUTHOR]

Abstract: Reducing the spacing between the magnetic head and the magnetic media is of crucial importance in enabling future high-density magnetic data storage. The magnetic spacing has been reduced to a level that we have to explore new schemes for the further reduction of the spacing. This paper reports authors’ efforts towards fly- and lubricant-contact recording scheme. The targeted objective is to minimize the mean-plane spacing between the slider and disk surfaces and to allow the further reduction of the overcoat thickness. The slider will still fly over the disk surface. The read/write head part of the slider will be protruded to contact lubricant—to minimize the mean-plane mechanical spacing. The key factors for achieving such a mechanism include super-smooth slider and disk surfaces, advanced slider air-bearing design to significantly reduce flying height modulation caused by disk waviness and flatness, nano-actuator design, position feedback control scheme to control the contact depth, and so on. The preliminary experimental data confirm the feasibility of such a lubricant-contact scheme. The slider air-bearing design presented in this work also indicates the feasibility of high-performance slider design, which can well follow the disk waviness. A parameter, anti-modulation factor, is introduced for the evaluation of slider''s performance in reducing flying height modulation caused by disk waviness. [Copyright &y& Elsevier]

We have investigated the effects of stray magnetic field upon a perpendicular magnetic recording (PMR) system, which consists of a single pole type head and a double-layered perpendicular medium. We found that fields in the plane of the disk could cause serious erasure. External magnetic flux concentrates around the edges of a return pole and can cause very large fields to appear in the medium. In addition, the writing operation significantly enhances this erasure. We called this kind of erasure "corner erasure." Experimental 2.5-inch hard disk drives (HDDs) were used to study the combined effect of the external field and write field. We checked SER degradation after applying an in-plane field of 0.8 kA/m (10 Oe). With no write-current applied, there is no degradation. However, as little as 0.8 kA/m (10 Oe) applied during writing causes severe degradation equivalent to that produced by a 4.0 kA/m (50 Oe) field applied when the head is reading on-track. It is concluded that the realization of PMR in commercial HDD would require new transducer designs to solve these problems. We devised a new return pole design which has a stepped-back wing to improve the robustness against in-plane stray fields. The alternative design greatly reduces the concentration of magnetic flux at the edges of return pole. Consequently, the stepped wing structure achieves about twice the robustness of the conventional rectangular return pole. A method was developed to allow external field sensitivity to be carefully checked. The method allows the degraded areas of data to be associated with the exact feature on the head that caused the problem. [ABSTRACT FROM AUTHOR]

Curvature of transitions recorded onto a magnetic disc has become more pronounced as tracks narrow. Curvature creates interference between adjacent transitions recorded at high bit density, and broadens the read back signal pulse. Curved transitions have a shape similar to that of the field contours that write them. A concave write pole trailing surface, or “U-pole”, pushes the field contours near the pole edges farther down track. This straightens the contours by partially compensating for transition curvature. We used a track trimming technique to compare transition curvature of flat poles and U-poles, and verified that the U-pole reduced curvature by more than 30%. We also demonstrated that the more curved transitions written by flat poles generate \sim1 nm more pulse broadening at the track edge relative to those written by U-poles. However, modeling predicts a \sim10% loss in down track field gradient near the center of a U-pole. Measurements of bit error rate across the track confirm the corresponding loss in U-pole performance relative to a flat pole over all but the outer portions of a track. [ABSTRACT FROM PUBLISHER]

Bit-patterned media (BPM) is a promising candidate for future high-capacity magnetic storage. The inter-track interference (ITI) in BPM has been taken into account by the “multiple islands per read head” model. However, the complexity of the symbol-based detection for this model is too high for practical use. To reduce complexity, we propose to use the reduced-state Bahl-Cocke-Jelinek-Raviv (BCJR) detection algorithm for such a two-dimensional model. We compare the computational complexity of the proposed reduced-state detector to that of the full-state BCJR detector. Simulation results show that the proposed reduced-state BCJR detector can approach the optimal performance by 0.5 dB while significantly reducing the detector complexity. [ABSTRACT FROM AUTHOR]

The authors report the enhancement of magnetic recording process by the combined field emission and moderate ionization between the write pole and magnetic media in a heat assisted magnetic recording experiment. When appropriate bias voltages are applied across the head-media gap, field emission from the write pole results in a sustainable moderate ionization without catastrophic air breakdown. The elevated media temperature from electron bombardment leads to reduced media coercivity. Our results show a 25% improvement to writing ability on perpendicular magnetic recording media using a modified read/write head. The effect of different combined emission/ionization currents with different read/write linear velocities was also studied. [ABSTRACT FROM AUTHOR]

To demonstrate the highest areal recording density of tape media, we have developed a metal evaporated tape with higher magnetic anisotropy of 2.5 × 105 J/m³ and finer magnetic activation volume of 2.7 × 10-24 m³ of a Co-CoO recording layer deposited on a smoother base film. A capability of an areal recording density of 23.0 Gb/in² was confirmed using a giant magnetoresistive head as a read head. The smoother surface roughness improved signal-to-noise ratio more than 2 dB. [ABSTRACT FROM AUTHOR]