Pin-Wei Huang

Using Ensemble Waveform Analysis to Compare Heat Assisted Magnetic Recording Characteristics of Modeled and Measured Signals

Ensemble waveform analysis is used to calculate signal to noise ratio (SNR) and other recording characteristics from micromagnetically modeled heat assisted magnetic recording waveforms and waveforms measured at both drive and spin-stand level. Using windowing functions provides the breakdown between transition and remanence SNRs. In addition, channel bit density (CBD) can be extracted from the ensemble waveforms using the di-bit extraction method. Trends in both transition SNR, remanence SNR, and CBD as a function of ambient temperature at constant track width showed good agreement between model and measurement. Both model and drive-level measurement show degradation in SNR at higher ambient temperatures, which may be due to changes in the down-track profile at the track edges compared with track center. CBD as a function of cross-track position is also calculated for both modeling and spin-stand measurements. The CBD widening at high cross-track offset, which is observed at both measurement and model, was directly related to the radius of curvature of the written transitions observed in the model and the thermal profiles used.

First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems

The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach.

Parametric Comparison of Modeled and Measured Heat-Assisted Magnetic Recording Using a Common Signal-to-Noise Metric

The auto-correlation signal-to-noise (ACSN) method is employed on micromagnetically modeled heat-assisted magnetic recording (HAMR) readback waveforms and compared with experimental ACSN data. The breakdown between transition signal-to-noise ratio (SNR) and remanence SNR is provided for both modeled and measured data. Good agreement is observed between both simulated and experimental SNRs as a function of laser power and as a function of linear density. An efficiency factor that relates maximum temperature observed in the media to the applied laser current is obtained by combining the modeled and experimental data. Usage of this methodology provides SNR metrics that allow a reliable comparison of micromagnetic modeling of HAMR recording systems to experimental measurements.

Importance of high magnetic field for HAMR SNR

In this work we develop a recording time window based model to estimate the writeability of granular media in heat-assisted magnetic recording.

Hybrid Design for Advanced Magnetic Recording Media : Combining Exchange-Coupled Composite Media with Coupled Granular Continuous Media

In order to enhance the performance of advanced granular recording media and understand the physics behind the mechanism of the reversal process, an atomistic spin-dynamics simulation is used to investigate theoretically the magnetic properties and the magnetization-reversal behavior for a composite media design. This model allows us to investigate the effect of the magnetostatic interaction and inter- and intralayer exchange coupling for a realistic system. The composite granular medium investigated consists of hard and soft composite layers in which the grains are well segregated with a continuous capping layer deposited to provide uniform exchange coupling. We present a detailed calculation aimed to reveal the reversal mechanism. In particular, the angular dependence of the critical field is investigated to understand the switching process. The calculations show a complex reversal mechanism driven by the magnetostatic interaction. It is also demonstrated, at high sweep rates consistent with the recording process, that thermal effects lead to a significant and irreducible contribution to the switching field distribution.

Data Rate Effects on Transition and Remanence Noise in a Modeled Heat-Assisted Magnetic Recording System

The heat-assisted magnetic recording performance at varying data rate conditions is investigated using an ensemble waveform analysis method. This method decouples the transition signal-to-noise ratio (SNR) and the remanence SNR from the total spatial media SNR. For data rates below 2200 Mbpsi, transition and remanence noises are largely independent of writer field rise time (RT) values less than 150 ps. Above a data rate of 2200 Mbpsi, the transition SNR is significantly degraded for the slowest RTs considered. For all data rate values, the remanence SNR sees minimal degradation with increasing RT. At the highest data rate, at least a 1 dB loss is observed compared with the lowest data rate, across the RT range considered. For comparison, spin-stand data were also collected. The modeled results were contrasted to bit error rate (BER) trends obtained from the measurement. The spin-stand data show a significant BER degradation as a function of increasing RT at higher data rates. This trend is likely explained with the increase in transition noise observed in the model. These results suggest that moderate writer field RTs do not degrade either transition or remanence noise significantly. If RTs can be kept low, higher data rates may be allowable from a media noise perspective.