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Coupled granular/continuous (CGC) perpendicular media with two different continuous layers, a Co/Pd multilayer and a CoCrPtB cap layer, were compared. It was confirmed that both thickness optimized layers functioned well as exchange coupled continuous layers. A Landau-Lifshitz-Gilbert simulation was performed for various grain boundary thicknesses, and the signal-to-noise ratio improvement predicted by the simulation was in good agreement with experiments. The CGC structure was susceptible to side erasure on account of its Stoner-Wohlfarth type magnetic switching, and the recording performance was dominated by the granular layer. Controlling this behavior would enable further improvement in recording density. The benefits of discrete-track media with the CGC structure are discussed. We found that ion irradiation of the CGC media could be effective to create soft magnetic regions in between recorded tracks, which act as guard bands, improving the recording performance. Index Terms--Discrete-track medium, exchange coupling, soft guard band, track edge noise.

The recording physics of bit-patterned media is studied for areal densities of around 2 Tbits/[inch.sup.2]. A model of the writing process, based on the head field gradient and switching field distribution, including various interference fields, is presented to extract the write-head and media parameters which are necessary to attain a wider write margin. Write head field distributions, calculated by the finite-element method, are presented for various head pole structures with side- and trailing-shields to improve head field gradient. Optimization of the pole configuration increased the gradient to over 500 Oe/nm for a head-to-soft magnetic under layer (SUL) spacing of 14 nm. Using the head field distribution, a recording performance analysis by micromagnetic simulation indicated that the write margin was improved. Position and size dispersions of the dots deteriorated the signal-to-noise ratio (SNR) and increased adjacent track erasure (ATE). Index Terms--Bit-patterned media, head field gradient, Landau-Lifshitz-Gilbert (LLG) simulation, perpendicular magnetic recording, single-pole head, switching field distribution.

FEM-boundary integral method micromagnetic software was used to analyze the recording field response of an indented magnetic head to high frequency recording currents (1-4 GHz). Next, micromagnetic simulations of heat-assisted magnetic recording were performed and the signal-tonoise ratio (SNR) calculated at high frequencies. With a soft magnetic underlayer, the head field was large enough and gave higher SNRs. The large head field strength at low frequency did not cause any deterioration of the SNR. [ABSTRACT FROM AUTHOR]

Jitter noise reduction can be achieved by controlling the position of magnetic grains, but write synchronization is needed to take advantage of the potential reduction. A periodic read-back response can be obtained from DC-erased bits, which is composed of rows of grains. In this paper, the feasibility of creating a clock signal for write synchronization using this periodicity of the readback response is investigated. As a result, it was confirmed that a clock signal can be created by using the precise periodicity of the read-back response. [ABSTRACT FROM AUTHOR]

In bit patterned media (BPM), a magnetic data storage medium is patterned into nanoscale magnetic islands each representing one binary digit (bit). The recording performance of BPM depends upon the variability of island position, geometry, and magnetic characteristics. To understand the impact of the distributions of these parameters on the performance of BPM a detailed statistical model of write-errors has been developed. The islands can either be single layer or two-layer exchange coupled composite (ECC) structures. The modeling of ECC islands was made possible by the development of a 2-spin model to calculate switching field, coercivity, and energy barrier as a function of applied field which enables medium design to be optimized for a non-uniform write head field. The statistical model predicts coercivities and error rates in good agreement with a micromagnetic model but at significantly lower implementation and computational cost and shows good agreement with experimental data from drag-test experiments at 500 Gbit/in2. The model enables the position tolerance of the write head to be determined from the magnetic characteristics of the write head and the storage medium and it is therefore a valuable system design tool. [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]

Stable oscillation is one of the most important factors for spin-torque oscillators (STOs) used in a microwave-assisted magnetic recording system. We use a micromagnetic, integrated STO model, in which the STO is inserted into the main pole–trailing shield (MP–TS) gap of a write head, and show that the rise time of the in-gap field acting on the STO is critical to stable STO oscillation. We also show that the combination of a tilted STO and a tilted MP–TS gap results in stable STO oscillation due to weaker magnetostatic interactions between the STO and the write head. [ABSTRACT FROM AUTHOR]

A micromagnetic model analysis was carried out considering two types of write heads and three types of spin-torque oscillators (STOs). For write heads, we considered a small-sized head to reduce calculation time and a large-sized head with dimensions close to commercial heads. For STOs, we used a double-layered STO with reflection spin torque, a double-layered STO with transmission spin torque, and a tri-layered STO with two spin injection layers. We also carried out micromagnetic simulations of the STOs without the write heads (isolated STO) to compare the oscillation states. It was found that, compared with isolated STOs in a uniform applied field, a larger applied field was necessary for STOs integrated into a write head. This result shows that the write head should be designed to generate a large, well-shaped gap field to ensure stable STO oscillation. [ABSTRACT FROM AUTHOR]

A model analysis was used to investigate a spin-transfer torque oscillator (STO) and magnetic write head for shingled microwave-assisted magnetic recording, where the interactions between STO and write head were included. The magnetic head had a tilted main pole (MP)–trailing shield (TS) gap with respect to the medium surface. The STO was placed in the tilted gap and off-center with respect to the MP center axis. The head structure allowed stable STO oscillation due to the lower in-plane field on the STO and large magnetic head field and high field gradient in the cross-track direction due to the wide pole. An off-centered STO in the MP–TS tilted gap had a stable oscillation at the cost of a slight reduction in oscillation amplitude. [ABSTRACT FROM AUTHOR]

Magnetic write heads were modeled and analyzed for thermally assisted magnetic recording combined with shingled recording, targeting an areal density of 8 Tbit/in \(^{2}\) and using the Storage Research Consortium (SRC, Japan) specifications. The head design has an indentation for the near field transducer and has a large recording field at the heat spot. Micromagnetic media recording simulations revealed that an areal density of more than 8 Tbit/in \(^{2}\) was possible with shingled recording, compared with 4.4 Tbit/in \(^{2}\) in a nonshingled system. Also, micromagnetic recording head simulations showed that reducing the magnetic head dimensions was effective for high frequency response. Finally, it is shown that a soft magnetic underlayer works quite well at high frequency to enhance the recording field. [ABSTRACT FROM AUTHOR]

We used a micromagnetic model to investigate the high-frequency (1–5 GHz) response, peak recording field strength, recording field gradient, and adjacent track erasure (ATE) field for various main pole tip, shield, and return yoke structures in planar type heads. The effect of the pole tip area at the air-bearing surface (ABS) and the return yoke structure is also discussed. It was found that the pole tip and shield arrangement had a major effect on the peak recording field strength, recording field gradient, and ATE field, i.e., the trailing and side shields work to reduce the undesired field, however, they also slow the head field response due to the interaction between the main pole tip and the shield. The field responses are also dependent on the main pole tip–shield structures and pole tip structures. The return yoke thickness and area were important determinants of response speed and peak field. [ABSTRACT FROM PUBLISHER]

Modeling of a simple writing process considering intergranular exchange fields and magnetostatic interaction fields between grains is studied for two-dimensional magnetic recording (TDMR). A new designing method of a two-dimensional neural network equalizer with a mis-equalization suppression function (2D-NNEMS) for TDMR is also proposed. The bit-error rate (BER) performance of a low-density parity-check coding and iterative decoding system with the designed 2D-NNEMS is obtained via computer simulation using a read/write channel model employing the proposed writing process under TDMR specifications of 4 Tb/in^2, and it is compared with those for one- and two-dimensional finite impulse response equalizers (FIREs). It is clarified that the BER performance for the designed 2D-NNEMS is far superior to those for the FIREs. [ABSTRACT FROM AUTHOR]

Planar type recording write heads were investigated using a micromagnetic analysis targeting a transfer-rate of 5 GHz. Six different planar head structures with various yoke widths, yoke heights, and coil locations were modeled. Six different conventional single-pole-type (SPT) write heads were also used for comparison. The material characteristics including the exchange constant, anisotropy energy, and Gilbert damping factor were also varied. It was found that the planar heads had a faster high-frequency response, a larger recording field, and a smaller ATE field. In the planar head, the most dominant factor for high transfer-rate recording was the coil location relative to the main pole tip and the return yoke height, while the yoke width was less important. Because the multi-turn coil can be realized with a wide yoke, it is advantageous in the planar head. With regard to the material characteristics, a small Gilbert damping factor was the most effective, while the other material characteristics did not yield significant differences. [ABSTRACT FROM AUTHOR]

Micromagnetic analysis was carried out to reduce the adjacent track erasure (ATE) field in planar type recording write heads. First, a quasi-static head field analysis showed that a three-step tapered pole had advantages over one-step and two-step poles. Next, dynamic micromagnetics proved that smaller models had higher recording fields and lower ATE fields compared with larger models. Finally, it was shown that the planar head had advantages over conventional, single-pole-type (SPT) heads in respect of its larger recording field, faster response to a high-frequency current and smaller ATE field. [ABSTRACT FROM AUTHOR]

Discrete track media (DTM) and bit-patterned media (BPM) are being extensively studied as routes to achieve higher density hard disk drives. In the DTM and BPM, it is essential to isolate the data tracks or bits with non-magnetic materials to reduce the magnetic noise from adjacent tracks or bits. In contrast to the conventional procedure of physically etching the media, we attempted to isolate the tracks or bits with soft regions using an area-selective ion irradiation method. We prepared hard and soft nano-composite structures by nanoimprinting, followed by ion irradiation. In this study, we confirmed the magnetic reversal process of the hard and soft regions of the nano-composite structure using magnetic force microscopy (MFM) with various external applied magnetic fields. The analysis of the magnetization reversal process of patterned Coupled Granular Continuous (CGC) films with weak exchange coupling confirmed the validity of this novel approach for the fabrication of DTM and BPM. [ABSTRACT FROM AUTHOR]

Head and medium designs to support areal densities of 400 Gb/in² were investigated using micromagnetic modeling. The use of side shields allows the track pitch to be reduced, but only by about 10 nm. Reducing the main pole width also permits higher track densities, but the erase band width does not reduce significantly with the pole width reduction. In addition, the erase band width increases at higher linear densities and forms an increasing fraction of the total track width. [ABSTRACT FROM AUTHOR]

A single-pole-type head design for 400 Gb/in² based on finite-element method (FEM) simulations is presented. The conditions required to generate a sufficient field for this areal density are shown. To reach this density various media were considered and written track widths, erase bands, signal-to-noise ratios, and written bit patterns were derived from Laudau-Lifshitz-Gilbert (LLG) simulations. [ABSTRACT FROM AUTHOR]

Head and medium designs to support areal densities of 400 Gb/in² were investigated using micromagnetic modeling. The use of side shields allows the track pitch to be reduced, but only by about 10 nm. Reducing the main pole width also permits higher track densities, but the erase band width does not reduce significantly with the pole width reduction. In addition, the erase band width increases at higher linear densities and forms an increasing fraction of the total track width. [ABSTRACT FROM AUTHOR]