Hans Jurgen Richter

The transition from longitudinal to perpendicular recording

After more than 30 years of research, hard disk drives using perpendicular recording are finally commercially available. This review is a follow-up of a review written in 1999 and addresses the basic physics of perpendicular recording with special emphasis on the read and the write process and the magnetic aspects of the recording media. The paper also surveys various technical difficulties which prevented an earlier implementation of perpendicular recording. The paper closes with a short overview of alternative technologies that allow even higher storage densities.

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

A comprehensive analysis of the areal density potential of bit-patterned media recording shows that the recording performance is dominated by written-in errors. The statistical fluctuations of the magnetic properties and the locations of the individual bits lead to error probabilities so that some dots are either not recorded at all or cannot be recorded in the time window necessary to ensure synchronized writing. 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 5Tbits∕in.2 are analyzed.

and Beyond

A non-destructive technique to measure the time dependence of remanent coercivity in thin film disks is suggested. It is found that typical thin film recording media show an increase in coercivity of about 25% when the length of the field pulse is decreased from /spl sim/50 ms down to 10 ns. Very thin magnetic films are found to have considerably larger changes in coercivity than thicker ones.

Recording potential of bit-patterned media

This article addresses the basic physics of the magnetic recording process with special emphasis on thin-film recording media for high-density magnetic recording. Magnetization reversal, recording theory as well as noise theory is reviewed. The onset of super-paramagnetism, which potentially limits the storage density, is discussed in detail.

Dynamic coercivity effects in thin film media

Areal density growth has enabled hard disk drives to continually fulfill the demands from new enterprise, desktop, and consumer applications. The demonstration of 100 Gb/in/sup 2/ is another milestone that was achieved recently and is described in this paper. The recording demonstration employed fully integrated magnetic recording heads and thermally stable multilayer antiferromagnetically coupled (AFC) media through a commercially available channel chip. At a track density of 149 ktpi and linear density of 680 kbpi, the achieved off-track capability with 5% track squeeze was 10% of the track pitch, while maintaining a raw bit-error rate (BER) of 10/sup -4/ or better. This yielded an areal density of 101 Gb/in/sup 2/ with measured on-track raw BER of 5/spl times/10/sup -5/.

Recent advances in the recording physics of thin-film media

It is a common understanding that superparamagnetic effects will eventually limit the maximum recording density of magnetic hard disk recording. This contribution reviews the theoretical concepts of noise in magnetic recording as well as the concepts of thermally activated magnetization reversal, The theoretical results are contrasted with experimental data. The findings clearly indicate that at some point, signal-to-noise ratio has to be compromised with the thermal stability of the written information.

Magnetic recording demonstration over 100 Gbit/In/sup 2/

Magnetic data storage is pervasive in the preservation of digital information, and the rapid pace of computer development requires ever more capacity. Increasing the storage density for magnetic hard disk drives requires a reduced bit size, previously thought to be limited by the thermal stability of the constituent magnetic grains. The limiting storage density in magnetic recording is investigated treating the writing of bits as a thermodynamic process. A “thermal writability” factor is introduced and it is shown that storage densities will be limited to 15 to 20 TBit/in2 unless technology can move beyond the currently available write field magnitudes.

Longitudinal recording at 10 to 20 Gbit/inch/sup 2/ and beyond

Thermal stability of the recorded information is generally thought to set the limit of the maximum possible density in magnetic recording. It is shown that basic thermodynamics always cause the probability of success of the write process to be less than 100%. This leads to a thermally induced error rate, which eventually limits the maximum possible density beyond that given by the traditional thermal stability limit. While the thermally induced error rate is negligible for recording of simple single domain particles, it rapidly increases in the presence of a write assist, in particular if the write assist is accomplished by an increased recording temperature. For the ultimate recording system that combines thermally assisted writing with a recording scheme that uses one grain per bit, the upper bound for the maximum achievable density is 20 Tbit/inch2 for a bit error rate target of 10−2.

Thermally induced error: Density limit for magnetic data storage

Composite grains, consisting of a subgrain with high anisotropy field coupled with a subgrain with zero anisotropy, are analyzed using a two-spin model. An analytical expression is given for the exchange coupling between the subgrains that minimizes the field required to reverse the magnetically hard layer. The results of the two-spin model are compared with those of a spin chain that represents an “exchange spring magnet.” The limitations of the two-spin model are worked out.