Magnetic Recording Systems Research Articles

Development, micro fabrication, and test of flexible magnetic write head for gentelligent applications

A “gentelligent component” inherently stores all information necessary for its distinct identification, reproduction as well as for its manufacturing process and thus has both genetic and intelligent character. For the data storage directly on the components’ rough surface a magnetic recording system is required. The goal is to develop a flexible magnetic write head which can adapt its own geometry to the components surface topography and guaranties perfect contact with the surface during the data storage process. This paper presents a new micro fabrication method using the fabrication without a rigid substrate base, double-sided fabrication, adhesive tape application, and high precision drilling. This method simplifies the fabrication process and offers modularity. The write head showed error-free performance after thermal shock test.

Numerical study of thermal-induced lubricant depletion induced on an anisotropic multilayer disk in a heat assisted magnetic recording system

This paper presents a numerical investigation of heat transfer and lubricant depletion on the hard disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures with anisotropic thermal properties on the top-recording layer and a thin layer of lubricant on the top surface. The heat generated by the laser results in the non-uniform temperature filed and subsequent lubricant depletion on the disk top surface. Two multilayer structures with different alloy materials on the top layer are studied. The results show that the top-layer alloy anisotropy does affect both temperature distribution and lubricant depletion, with the extent of the effect depending on the thermal diffusivity ratio (defined as the ratio of the thermal diffusivity along x–y direction to that along z direction on the top layer) as well as the alloy material of the top layer. For the top-layer alloy with inferior thermal properties, the effect of anisotropy is more significant at the range of thermal diffusivity ratio from 1 to 0.5. With a further reduction in this ratio, the anisotropy of the top-layer material does not show further noticeable effect.

Transition Noise Analysis of Recording Media With a Soft Underlayer (SUL) and an Antiferromagnetic Soft Underlayer (AF-SUL)

A perpendicular magnetic recording system has been modeled for the purpose of analyzing transition noise, particularly “jitter.” Conventional perpendicular media and “soft” exchange coupled composite (ECC) media with a conventional soft underlayer (SUL) and an antiferromagnetic soft underlayer (AF-SUL) have been investigated using micromagnetic simulation. The fast Fourier transform (FFT) technique and graphics processing unit (GPU)-based computing have been used to reduce the intensive computation time for magnetostatic interactions between the head, SUL, and recording layer. Interestingly, the jitter is always less dependent on reader offset from track center with the AF-SUL. Jitter for ECC media is also shown to depend less strongly on reader offset than for conventional media. The transition center deviation at the optimal anisotropy for both recording layers is lower with the AF-SUL at both linear densities considered. We further find that the track center moves alternately with direction of fringing field as expected from magnetostatic considerations.

Laser-induced local heating and lubricant depletion in heat assisted magnetic recording systems

The present study concerns the depletion of thin lubricant film on a disk surface subject to repeated heating by a scanning laser in a heat assisted magnetic recording (HAMR) system. The absorption rate of optical energy by the disk medium is derived from Maxwell equations, which is incorporated into the energy equation by a source term. Both the temperature and the temperature gradient have important effects on lubricant thickness, which, in turn, influences lubricant dynamics and evaporation via the disjoining pressure. The heat loss via convection from the disk surface becomes significant only when the convective heat transfer coefficient is bigger than 109W/(Km2). With an increase in the absorption coefficient β, the maximum temperature on the disk increases while the heat penetrating depth decreases. For the same energy absorptivity, the surface temperature and, in consequence, lubricant depletion, predicted by the present optical absorption model is lower than that obtained by simplifying the laser heating as a heat flux at the disk surface. By adjusting empirical absorptivity, the heat flux model can produce the same heat transfer results and, in consequence, the same lubricant depletion results, as those predicted by the optical absorption model only when β⩾108m−1.

Intelligent operating theater: Technical details for information broadcasting and incident detection system

This paper introduces an intelligent operating theater equipped with a magnetic resonance imaging (MRI) scanner and video recording and broadcasting system to enhance the quality of surgery. To reduce error, intraoperative incidents are detected and dealt with using semi-automatic computer algorithm. A multiple-channel video recording and broadcasting system was installed in an operating room and the surgical procedure was recorded. The supervising surgeon monitored the operation in real-time from outside the operating room. Information sharing via the intra-hospital network improved the work efficiency of staff. The amount of motion was estimated from recorded file size based on the principle of inter-frame video compression. A time period for which the file size significantly increased compared to those for neighboring time periods was chosen and the majority voting technique was applied to detect events using six channels of the video. A change in file size indicated a phase change of the surgical procedure. The proposed method is promising for future daily clinical procedure.

Detection for Two-Dimensional Magnetic Recording Systems

Detection for Two-Dimensional Magnetic Recording Systems

A Numerical Study on Heat Transfer and Lubricant Depletion on an Anisotropic Multilayer Hard Disk

This paper presents a numerical investigation on the effect of thermal anisotropy of the top layer alloy on heat transfer and lubricant depletion on the disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures and a thin layer of lubricant on the top surface. Cases under different laser powers and initial lubricant film thicknesses are examined. The top-layer alloy thermal anisotropy does show non-negligible effect on the heat transfer and lubricant depletion. With the top-layer alloy being more anisotropic, higher temperature increase and lager lubricant depletion can be observed on the disk surface. The results also show that the thermal anisotropy effect is more significant under a lower laser power but nearly keeps no much difference under different initial lubricant film thicknesses. Thus it is of importance to include the thermal anisotropy effect of the top-layer Co-alloy when simulating the heat transfer and lubricant depletion in practical multilayer HMAR systems, especially for the cases under the condition of lower laser power, as the effect cannot be neglected under such conditions.

An Alternative Design of Light Delivery System for Heat-Assisted Magnetic Recording

The light delivery system is an important component in heat-assisted magnetic recording technology. It needs a light source and delivery the laser beam to the slider for writing process. However, the different designs lead to the different manufacturing processes, number of process steps and technologies consequently affect to the fabrication cost. This paper aims to propose an alternative design for a light delivery system. The complicated processes to manage a heat in a manufacturing are also take into account to have the final product meets the requirement for HAMR technology. The components are also fabricated which is made for a design and also presented.

Modified Graph-Based Detection Methods for Two-Dimensional Interference Channels

Two-dimensional (2-D) interference channels with inter-symbol interference (ISI) and inter-track interference (ITI) exist in the magnetic recording systems at high areal density. A number of 2-D detection methods have recently been proposed for the multi-track processing of the 2-D channels. Graph-based detector with the belief propagation algorithm appears as an alternative method, but at a degraded performance and high complexity level. In this work, we propose two methods to modify the graph-based (GB) detector. One applies a serial scheduling to the GB detector, while the other modifies the GB detection by ignoring some connections during one direction of the reliability updates in the factor graph leading to the reduction of short cycles. The simulation results show that the proposed GB detectors give better bit error rate performances than the other GB detectors.

Off-Track Detection Based on the Readback Signals in Magnetic Recording

Off-track condition in magnetic recording systems degrades the system performance. It is typically detected and adjusted by the servo control loop. In this work, we propose an off-track detection based on the readback signals and improve the bit error performance using an asymmetric target depending on the detected off-track direction. Specifically, we investigate the effects of off-track events on the target-shaping equalizer coefficients when the generalized partial-response target (GPR) is fixed. For a 3 t 3 channel matrix of bit patterned media recording (BPMR) system, the asymmetric targets offer the gain of about 1 to 2 dB at BER=10-4 for the TMR level of 20% to 25%.

Ideas for Detection in Two-Dimensional Magnetic Recording Systems

In two-dimensional magnetic recording, detection for a perfect writer and perfect reader based on an iterative threshold technique are compared to detection employing single threshold and adaptive threshold techniques. The simulation indicates that the algorithm can reach a BER of 9.3% compared to 11.2% and 10.5% for the latter cases when the bit size is 8 by 8 nm with a grain of 8.7 nm diameter. This increases data capacity by 11% to 6.6 TBits/inch2. Additionally, detection with an array of three conventional heads has been studied: the simulation shows that for bits with dimension of 12 × 12 nm, grains of 8.7 nm diameter and reader width of 18 nm, the BER drops from 11.3% for a single conventional head to 5.4% for the head array with a two-dimensional generalized partial response equalizer at the optimum offset of 10 nm. The density is increased by 42%, reaching 4.0 Tbits/Inch2 .

Two-Dimensional Voronoi-Based Model and Detection for Shingled Magnetic Recording

In this paper, we present a model of a shingled magnetic recording system, where Voronoi regions are used to model the grains of the magnetic medium. A probabilistic model is used to represent imperfections in the write process, i.e., the head failing to write some grains correctly. A two-dimensional model of the head response is used to calculate the signal read back by the head over any place on the medium, thereby including both intertrack and intersymbol interference effects in the model. We also present simulation results from tests of this model using a multitrack detector and an intertrack interference canceller and give performance results of the channel/detector combination for various track offsets.

Microfocal lens for energy-assisted magnetic recording technology

In this Letter an original method is proposed to assist optical coupling in energy-assisted magnetic recording systems by introducing a microfocal lens. Simulation results show that the lens effectively reduces the incident light spot size to subwavelength scale, which benefits the magnetic recording density. The proposed microfocal lens can be manufactured at low cost because its fabrication is compatible with the conventional magnetic read/write head process.

열 보조 자기기록 시스템 헤드의 touch-down 과 take-off 해석

In HDD industry, many technologies have been developed and investigated as means to increase the areal density of drives. Especially, heat assisted magnetic recording (HAMR) system has been considered as the next generation storage device. Most of the HAMR systems use near field optics as heating mechanism. Therefore, light delivery system is indispensable. We considered the light delivery system with laser diode (LD) mount and optical fiber. Mass and stiffness of the HAMR system using these LD mount and optical fiber are changed. The mass and stiffness of the HAMR system affects the slider dynamic behavior. It is necessary to analyze touch down (TD) and take off (TO). And, we performed the TD-TO experiment with HAMR suspension. Finally, we analyzed the result of TD-TO experiments. And we suggested the design of HAMR suspension to improve TD-TO performance.

On the lifetime of plasmonic transducers in heat assisted magnetic recording

For a heat assisted magnetic recording system to be successful, it must deliver heat to a small spot on a magnetic disk without being damaged by the applied power. This paper shows that such conditions may not be easily attained in systems that use laser energy and plasmonic near field transducers. It is also shown that the analysis and design of the near field transducers cannot rely on numerical integration of the conventional Maxwell equations of electrodynamics of continuous media, because such equations implicitly incorporate numerous assumptions that are not valid in nanoscale systems. Here, we examine assumptions inherent in the derivation of these equations and point out which assumptions are violated if they are applied to the metallic nanoscale elements of heat assisted magnetic recording systems. The main body of the paper focuses on the well-known experimental results that support our conclusions while the derivations are relegated to the appendices.

Magnetic properties of elliptical and stadium-shaped nanoparticles: Effect of the shape anisotropy

Elliptical and stadium-shaped nanoparticles as a function of their geometry have been investigated using numerical simulations. The effect of the shape anisotropy of the particles on coercivity and remanence together with the angular dependence of the remanence and coercivity are addressed. Our results demonstrate that the stadium-shaped particles have many of the outstanding properties of elliptical particles, but also have unique properties, such that the coercivity and remanence remain stable for a wide range of geometry parameters, and exhibit a peculiar angular dependence in the coercivity. These properties suggest that they can be useful for applications in the area of magnetic recording systems.

Mechanisms of heat transport across a nano-scale gap in heat assisted magnetic recording

This paper compares different mechanisms of heat transport across nano-scale gaps and discusses the role of electromagnetic phenomena in heat transport in general nano-scale layered structures. The results of the analysis suggest that heat transfer across sub-5 nm gaps like that appearing in prototypes of heat assisted magnetic recording (HAMR) systems is dominated by direct intermolecular interactions between the separated bodies and is little affected by electromagnetic radiation. The analysis further suggests that local heating for HAMR with sub-5 nm spacing can be more efficiently achieved by a Joule heater that is simpler to fabricate than laser-based optical systems and is less destructive for the nano-scale transducers than laser radiation, which may lead to their structural damage and short duration life of nanoscale transducers.

Time Domain Analysis Of Nanoscale Electromagnetic Problems By A Boundary Integral Equation Method With Fast Inverse Laplace Transform

A novel computational technique is proposed for analysis of transient electromagnetic problems in nanoscale. Our proposed method can perform reliable and efficient simulation. We discuss time domain analysis of a nanoscale antenna to establish an ultra-fast and high-density magnetic recording system.

Comparing Analytical, Micromagnetic and Statistical Channel Models at 4 Tcbpsi Patterned Media Recording

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.

Unequal error correction strategy for magnetic recording systems with multi-track processing

In multi-track detection, the simultaneous recovery of user data of all tracks is obtained from multi-head or single-head reader with buffer. Due to incomplete inter-track interference (ITI) information of the outer tracks, unequal error rates exist among tracks. For a system with three-track processing, the center track exhibits a better performance than the others. In this work, we propose the unequal error protection (UEP) schemes to improve the overall system performance of a 2-D interference bit-patterned recording system with multi-track detection. The performances of the proposed schemes are investigated for the BPM channels with and without the media noise. Based on the simulation results, the proposed schemes offer the gain of about 0.2–0.3 dB over the equal error protection (EEP) scheme at a bit error rate of 10−4.