Richard Michael Brockie

Recording on Bit-Patterned Media at Densities of 1 Tb/in

We present a comprehensive analysis of the areal density potential of a bit-patterned media recording. The recording performance is dominated by written-in errors rather than traditional signal-to-noise considerations. Written-in errors are caused by statistical fluctuations of the magnetic properties and the locations of the individual dots. The highest areal densities are obtained with a combination of a pole head, a soft magnetic underlayer, and a storage medium of the composite type. Areal density scenarios of up to 5 Tb/in2 are analyzedRecording on bit-patterned media, BPM, is one way to postpone the superparamagnetic limit to higher densities. Here we investigate the recording potential of BPM. The fundamental idea of bit-patterned media is that one grain represents one bit so that the entire volume of the bit resists the effect of thermal agitation and higher recording density can be achieved. Previous investigations of a BPM recording system have shown that recording densities greater than 1 Tb/in2 should be possible [2].

^2

CoCrPt(B) media with high magnetic anisotropy have been fabricated at a thin magnetic layer thickness (10 nm) and a thin interlayer thickness (4 nm). The hard magnetic properties of the CoCrPt enable addition of boron, which aids to magnetically decouple the grains. These media are thermally stable and have an enhanced signal-to-noise ratio.

and Beyond

We present experimental and theoretical data on the signal decay of recordings measured at various densities. In contrast to expectations, the signal decay does not generally increase with increasing linear density; rather, it peaks at a surprisingly low density. Using a nondestructive spin-stand technique, we determined the energy barrier as well as the anisotropy field distribution. These experimental data are used in a self-consistent recording model that accounts for thermal activation effects at writing as well as at storage. We found that the record process inevitably induces phase shifts in the recorded pattern that lead to the observed decay behavior.

High anisotropy CoCrPt(B) media for perpendicular magnetic recording

Using a ldquodragrdquo tester in which the recording head is in direct contact with a perpendicular media disc, we show experimentally that the footprint of the head has a ldquodoughnutrdquo shape, as predicted by theory. A change in the switching properties of the media, from coherent rotation in conventional perpendicular media to incoherent rotation in exchange spring media, can be detected through the transformation of the head footprint, from ldquodoughnutrdquo to a dome-like shape.

Linear density dependence of thermal decay in longitudinal recording

Combining antiferromagnetically coupled (AFC) and laminated media (LM), we were able to incorporate the stability of AFC media with the signal-to-noise ratio (SNR) of LM. This improvement is directly related to the decrease of the demagnetization field which is calculated to be up to 50% of the LM case for some configurations of AFC+LM that were experimentally realized. The stabilization layer also increases the magnetic energy barrier of the recording layers in the AFC+LM structure, which further improves the stability of this media. An improvement of ∼1 dB in SNR was observed in AFC+LM in comparison to single layer media.

Effect of Media Reversal Mode on Head Footprint

Exponential growth of the areal density has driven the magnetic recording industry for almost sixty years. But now areal density growth is slowing down, suggesting that current technologies are reaching their fundamental limit. The next generation of recording technologies, namely, energy-assisted writing and bit-patterned media, remains just over the horizon. Two-Dimensional Magnetic Recording (TDMR) is a promising new approach, enabling continued areal density growth with only modest changes to the heads and recording electronics. We demonstrate a first generation implementation of TDMR by using a dual-element read sensor to improve the recovery of data encoded by a conventional low-density parity-check (LDPC) channel. The signals are combined with a 2D equalizer into a single modified waveform that is decoded by a standard LDPC channel. Our detection hardware can perform simultaneous measurement of the pre- and post-combined error rate information, allowing one set of measurements to assess the absolute areal density capability of the TDMR system as well as the gain over a conventional shingled magnetic recording system with identical components. We discuss areal density measurements using this hardware and demonstrate gains exceeding five percent based on experimental dual reader components.

Different designs and limits of longitudinal magnetic recording media

Summary form only given. To date, most published measurements of the thermal stability of magnetic recordings on thin film media have been of single tone (ST, square wave or all-ones pattern) recordings. An all-ones pattern stores no information and by necessity, information is therefore stored in a magnetization pattern containing many different frequency components. A pattern containing information is not expected to decay as strongly as a single tone written at the frequency of the highest frequency component. A simple superposition of the demagnetizing fields associated with one transition shows that the average demagnetizing field is higher for an ST than for a pseudo-random sequence (PRS) pattern. The decay is accelerated by demagnetizing fields and therefore one expects ST signals to decay more quickly than PRS signals. To mimic application conditions more closely, we have investigated the decay of the components of a 15-tone PRS pattern and compare this with the decay of single tone patterns spanning the frequency range.

Spinstand demonstration of areal density enhancement using two-dimensional magnetic recording (invited)

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.

Thermal decay study of various magnetization patterns

Media thermal stability is characterized by using spin-stand tests for both signal and signal-to-noise ratio (SNR) decay. Agreement is shown between vibrating sample magnetometer (VSM) and spin-stand evaluations of the thermal decay rate dependence on linear density. For an equalized system, there is linear correlation between measured SNR and signal decay rates. Equalization to targets with DC content will result in higher decay

Definition of an Areal Density Metric for Magnetic Recording Systems

Thermal stability measurements of thin-film magnetic media are vital in determining the credibility of a medium design. Using our measurement technique, a series of thermal decay measurements have been performed to investigate the effect of various writing conditions. We find that as writing performance degrades, the measured thermal decay increases and that one must ensure that the medium is saturated at writing prior to a thermal stability measurement. It is therefore crucial that a decay test be carried out correctly, otherwise one runs the risk of rejecting stable medium designs.