J.J. Miles

The Feasibility of Magnetic Recording at 10 Terabits Per Square Inch on Conventional Media

This paper proposes a new approach to magnetic recording based on shingled writing and two-dimensional readback and signal-processing. This approach continues the use of conventional granular media but proposes techniques such that a substantial fraction of one bit of information is stored on each grain. Theoretically, areal-densities of the order of 10 Terabits per square inch may be achievable. In this paper we examine the feasibility of this two-dimensional magnetic recording (TDMR) and identify the significant challenges that must be overcome to achieve this vision.

Recording technologies for terabit per square inch systems

It is believed that areal densities approaching one terabit per square inch will ultimately be achieved with conventional magnetic recording technology. Such densities require that very sharp transitions be written on well-defined extremely narrow tracks in a very finely grained thermally stable recording medium. These requirements drive the key characteristics and geometries of the read and write heads and of the recording medium itself. This paper re-examines several aspects of a proposed terabit per square inch recording system and discusses some of the critical technologies required to support such extreme areal densities. These include the necessity of very low magnetic spacing, the ability to fabricate very narrow-track write/read heads, and the need for exquisite track-following capability. One of the biggest challenges at these extreme areal densities will be to develop a recording system that can also deliver very high data rates.

Time resolved micromagnetics using a preconditioned time integration method

A detailed description for the solution of the Landau–Lifshitz–Gilbert equation with the finite element method is given. The use of implicit time integration schemes with proper preconditioning is reported. Simulations of a single-phase magnetic nanoelement without surface roughness and a magnetic nanoelement with a granular structure are performed to investigate the influence of the microstructure on the numerical behavior. Nanoelements with a granular structure cause an inhomogeneous computational grid. In granular systems preconditioning for time integration speeds up the simulations by three orders of magnitude as compared to conventional time integration schemes like the Adams method. r 2002 Elsevier Science B.V. All rights reserved.

Channel Models and Detectors for Two-Dimensional Magnetic Recording

Two-dimensional magnetic recording (TDMR) is a novel recording architecture intended to support densities beyond those of conventional recording systems. The gains from TDMR come primarily from more powerful coding and signal processing algorithms that allow the bits to be packed more tightly on the disk, and yet be retrieved with acceptable error rates. In this paper, we present some preliminary results for an advanced channel model based on micromagnetic simulations, coined the Grain Flipping Probability model. This model requires a one-time computationally complex characterization phase, but subsequently provides fast and accurate two-dimensional (2-D) readback waveforms that include effects captured from micromagnetic simulations and the statistical effects derived from the granularity of the recording medium. We also show the performance of several detectors over a pre-existing TDMR channel model directly as a function of channel density rather than the signal-to-noise ratio (SNR).

TDMR Platform Simulations and Experiments

Two-dimensional magnetic recording (TDMR) is a novel architecture for magnetic recording systems proposed to achieve densities towards 10 Tb/in2. TDMR differs from other solutions in that it does not require a complete redesign of the head or medium for its gains, relying instead on powerful 2-D codes and signal processing to reliably store and retrieve the information. To explore the viability of TDMR via simulation, models for the 2-D medium, writing, and readback are needed. In this paper, we propose models for these processes and discuss ongoing progress in 2-D experimental waveform retrieval that will be used to validate the models. We show some initial results achieved using these models which demonstrate the viability of TDMR and that will provide an indication of what densities may be possible with TDMR, when the 2-D codes and detectors are completed.

A hierarchical micromagnetic model of longitudinal thin film recording media

Abstract A hierarchical method for the calculation of interaction fields in micromagnetic models of materials is discussed. The method is shown to provide a substantial decrease in the number of calculations required, whilst overcoming some inherent disadvantages of the mean field calculation. The method is employed in a micromagnetic model of longitudinal thin film recording media, with which the effects of intergranular exchange coupling upon hysteresis properties and recorded transitions are investigated.

The role of microstructure in micromagnetic models of longitudinal thin film magnetic media

A micromagnetic model of thin-film media in which the assumed microstructure of the film may be freely varied is presented. A variety of simulation results illustrating the role of microstructure are presented. It is concluded that the magnetic properties of thin films are determined not only by the properties of individual grains and the nature of the coupling between them, but also by the spatial arrangement of grains, or the microstructure of the film. In micromagnetic models, the choice of a particular, assumed microstructure will affect the predicted reversal mode and thus the hysteresis properties of the film. More significantly, the assumed microstructure may totally dominate the development of small-scale structures such as sawtooth transitions, flux closure, and magnetization ripple. It must therefore be expected that microstructure plays an important role in the prediction of media noise, and in the performance of real media. >

Approximate three-dimensional head fields for perpendicular magnetic recording

This paper proposes a method for obtaining approximate, but very accurate, three-dimensional (3-D) head fields for perpendicular magnetic recording heads. The method uses an assumed form for the scalar magnetic potential variation between a pole or shield and the underlayer to give the potential in the head/shields-face plane. It then uses this approximate air-bearing surface potential to find the potential or field components at any other position of interest. The approach is illustrated here by applying it to a symmetric double-shielded single-pole head with an underlayer and with side shields.

An accurate and efficient 3-D micromagnetic simulation of metal evaporated tape

Abstract Metal evaporated tape (MET) has a complex column-like structure in which magnetic domains are arranged randomly. In order to accurately simulate the behaviour of MET it is important to capture these aspects of the material in a high-resolution 3-D micromagnetic model. The scale of this problem prohibits the use of traditional scalar computers and leads us to develop algorithms for a vector processor architecture. We demonstrate that despite the materials highly non-uniform structure, it is possible to develop fast vector algorithms for the computation of the magnetostatic interaction field. We do this by splitting the field calculation into near and far components. The near field component is calculated exactly using an efficient vector algorithm, whereas the far field is calculated approximately using a novel fast Fourier transform (FFT) technique. Results are presented which demonstrate that, in practice, the algorithms require sub-O( N log( N )) computation time. In addition results of highly realistic simulation of hysteresis in MET are presented.

Remanence curves of longitudinal thin films

A micromagnetic model has been developed which is applied to the calculation of the principal remanence curves of a longitudinal thin film. The isothermal remanent magnetization curve (IRM) relies on the production of a realistic erased state. The authors developed an approach based on simulated annealing which produces a highly correlated demagnetized state. Comparison between the two curves via the Wohlfarth relation shows that the interparticle interactions are predominantly negative in a dipolar coupled thin film, indicating that exchange coupling is necessary in order to explain previously published experimental data. >