Physics:Magnetic storage

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Short description: Recording of data on a magnetizable medium
Longitudinal recording and perpendicular recording, two types of writing heads on a hard disk

Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.


History

The programmable calculators of the HP-41-series (from 1979) could store data via an external magnetic tape storage device on Mini-Cassettes.

Magnetic storage in the form of wire recording—audio recording on a wire—was publicized by Oberlin Smith in the Sept 8, 1888 issue of Electrical World.[1] Smith had previously filed a patent in September, 1878 but found no opportunity to pursue the idea as his business was machine tools. The first publicly demonstrated magnetic recorder, at Paris Exposition of 1900, was invented by Valdemar Poulsen in 1898. Poulsen's device recorded a signal on a wire wrapped around a drum. In 1928, Fritz Pfleumer developed the first magnetic tape recorder. Early magnetic storage devices were designed to record analog audio signals. Computers and now most audio and video magnetic storage devices record digital data.

Design

Hard drives use magnetic memory to store giga- and terabytes of data in computers.

The magnetic surface is conceptually divided into many small sub-micrometer-sized magnetic regions, referred to as magnetic domains, (although these are not magnetic domains in a rigorous physical sense), each of which has a mostly uniform magnetisation. Due to the polycrystalline nature of the magnetic material, each of these magnetic regions is composed of a few hundred magnetic grains. Magnetic grains are typically 10 nm in size and each form a single true magnetic domain. Each magnetic region in total forms a magnetic dipole which generates a magnetic field. In older hard disk drive (HDD) designs the regions were oriented horizontally and parallel to the disk surface, but for newer disks, the orientation was changed to perpendicular to allow for closer magnetic domain spacing.[2]

Older hard disk drives used iron(III) oxide (Fe2O3) as the magnetic material, but current disks use a cobalt-based alloy.[3]


A write head magnetises a region by generating a strong local magnetic field, and a read head detects the magnetisation of the regions. Early HDDs used an electromagnet both to magnetise the region and to then read its magnetic field by using electromagnetic induction. Later versions of inductive heads included Metal In Gap (MIG) heads and thin-film heads. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in read heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.[4]


Magnetic recording classes

Analog recording

Analog recording is based on the fact that remnant magnetisation of a given material depends on the magnitude of the applied field. The magnetic material is normally in the form of tape, with the tape in its blank form being initially demagnetised. When recording, the tape runs at a constant speed. The writing head magnetises the tape with current proportional to the signal. A magnetisation distribution is achieved along the magnetic tape. Finally, the distribution of the magnetisation can be read out, reproducing the original signal. The magnetic tape is typically made by embedding magnetic particles (approximately 0.5 micrometers [5] in size) in a plastic binder on polyester film tape. The most commonly used of these was ferric oxide, though chromium dioxide, cobalt, and later pure metal particles were also used. Analog recording was the most popular method of audio and video recording. Since the late 1990s, however, tape recording has declined in popularity due to digital recording.[6]

Digital recording

Instead of creating a magnetisation distribution in analog recording, digital recording only needs two stable magnetic states, which are the +Ms and −Ms on the hysteresis loop. Examples of digital recording are floppy disks, hard disk drives (HDDs), and tape drives. HDDs offer large capacities at reasonable prices; as of 2024, consumer-grade HDDs offer data storage at about US$15–20 per terabyte.[7]

Magneto-optical recording

Domain propagation memory

Technical details

Access method

Coding schemes

Magnetic disk heads and magnetic tape heads cannot pass DC (direct current), so the coding schemes for both tape and disk data are designed to minimize the DC offset. Most magnetic storage devices use error correction.[8]


Current usage

As of 2021, common uses of magnetic storage media are for computer data mass storage on hard disks and the recording of analog audio and video works on analog tape. Since much of audio and video production is moving to digital systems, the usage of hard disks is expected to increase at the expense of analog tape. Digital tape and tape libraries are popular for the high capacity data storage of archives and backups. Floppy disks see some marginal usage, particularly in dealing with older computer systems and software. Magnetic storage is also widely used in some specific applications, such as bank cheques (MICR) and credit/debit cards (mag stripes).

Future

A new type of magnetic storage, called magnetoresistive random-access memory or MRAM, is being produced that stores data in magnetic bits based on the tunnel magnetoresistance (TMR) effect. Its advantage is non-volatility, low power usage, and good shock robustness. The first generation that was developed was produced by Everspin Technologies, and utilized field induced writing.[9] The second generation is being developed through two approaches: thermal-assisted switching (TAS)[10] which is currently being developed by Crocus Technology, and spin-transfer torque (STT) on which Crocus, Hynix, IBM, and several other companies are working.[11] However, with storage density and capacity orders of magnitude smaller than a hard disk, MRAM is useful in applications where moderate amounts of storage with a need for very frequent updates are required, which flash memory cannot support due to its limited write endurance. Six state MRAM is also being developed, echoing four bit multi level flash memory cells, that have six different bits, as opposed to two.[12]

Research is also being done by Aleksei Kimel at Radboud University in the Netherlands[13] towards the possibility of using terahertz radiation rather than using standard electropulses for writing data on magnetic storage media. By using terahertz radiation, writing time can be reduced considerably (50x faster than when using standard electropulses). Another advantage is that terahertz radiation generates almost no heat, thus reducing cooling requirements.[14]

See also

References

  1. ↑ Ley, Willy (August 1965). "The Galactic Giants". Galaxy Science Fiction: 130–142. https://archive.org/stream/Galaxy_v23n06_1965-08#page/n129/mode/2up. 
  2. ↑ Piramanayagam, S. N.; Srinivasan, K (2009). "Recording media research for future hard disk drives". Journal of Magnetism and Magnetic Materials 321 (6): 485–494. doi:10.1016/j.jmmm.2008.05.007. Bibcode: 2009JMMM..321..485P. https://d1wqtxts1xzle7.cloudfront.net/30672529/14660326-libre.pdf?1391834659=&response-content-disposition=inline%3B+filename%3DRecording_media_research_for_future_hard.pdf&Expires=1746710324&Signature=KphFpUPbJk6qxNJuxSMEEo6g2RnFqQasq~BiZ1~DcB3iS7DQCTDiFooJu~faJ6VbJsJ-Y6l-IDzh0-vRWmM-Ed5b7PK0bE7XmddsZqPvz2BaOYrLF4k60FoHwZ-Ex4TxHQ6k7cwRj3z6bP2ULUk1FmI7p2wP3fQR7uXgOfkari-NRYkRT2IDSUrh-C0gKc3fzoRhYrKiqtZU8~-iwQGaKLX6mxQw2dw0ZEHEjz7La-M2Y3Ja3sV5yMyezqF9X1~Hou8Q36-DzNprZvfmeSL0IRC~5osRpSGFrkmJMQYdCeD2Sw1RW2EgiXsccNA3XVtl3ke~nTj6dq1Xxk7FgnJeHw__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA. 
  3. ↑ Kanellos, Michael (24 August 2006). "A divide over the future of hard drives". CNETNews.com. http://news.cnet.com/A-divide-over-the-future-of-hard-drives/2100-1008_3-6108687.html. 
  4. ↑ "IBM OEM MR Head | Technology | The era of giant magnetoresistive heads". Hitachigst.com. 27 August 2001. https://www1.hitachigst.com/hdd/technolo/gmr/gmr.htm. 
  5. ↑ "Magnetic Tape Recording". Hyperphysics.phy-astr.gsu.edu. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape2.html. 
  6. ↑ E. du Trémolete de Lacheisserie, D. Gignoux, and M. Schlenker (editors), Magnetism: Fundamentals, Springer, 2005
  7. ↑ "Disk Prices (US)". Legitimate Data Company LLC.. https://diskprices.com/.  Prices are lower for used/refurbished drives.
  8. ↑ Allen Lloyd. Complete Electronic Media Guide. 2004. p. 22.
  9. ↑ "MRAM Technology Attributes". http://www.everspin.com/technology.html. 
  10. ↑ The Emergence of Practical MRAM "Archived copy". http://www.crocus-technology.com/pdf/BH%20GSA%20Article.pdf. 
  11. ↑ "Tower invests in Crocus, tips MRAM foundry deal". EE Times. http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=218000269. Retrieved 2014-01-28. 
  12. ↑ "Researchers design six-state magnetic memory". http://phys.org/news/2016-05-six-state-magnetic-memory.html. 
  13. ↑ "Prof. Kimel, A.V. (Aleksei) | Radboud University". https://www.ru.nl/en/people/kimel-a. 
  14. ↑ Kijk magazine, 12, 2019



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