Editing Superparamagnetism (section)

==Effect on hard drives==
Superparamagnetism sets a limit on the storage density of [[hard disk drive]]s due to the minimum size of particles that can be used. This limit on [[Areal density (computer storage)|areal-density]] is known as the '''superparamagnetic limit'''.

* Older hard disk technology uses [[longitudinal recording]]. It has an estimated limit of 100 to 200 Gbit/in<sup>2</sup>.<ref>{{cite conference |last1=Kryder |first1=M. H. |title=Magnetic recording beyond the superparamagnetic limit |work=Magnetics Conference, 2000. INTERMAG 2000 Digest of Technical Papers. 2000 IEEE International |year=2000 |page=575 |doi=10.1109/INTMAG.2000.872350|isbn=0-7803-5943-7 }}</ref>
* Current hard disk technology uses [[perpendicular recording]]. {{As of|2020|7}} drives with densities of approximately 1 Tbit/in<sup>2</sup> are available commercially.<ref>{{cite web| url = https://www.computerhistory.org/storageengine/hdd-areal-density-reaches-1-terabit-sq-in/| title = Computer History Museum: HDD Areal Density reaches 1 terabitper square inch}}</ref> This is at the limit for conventional magnetic recording that was predicted in 1999.<ref>{{cite journal| url = https://ieeexplore.ieee.org/document/824422| title = R. Wood, "The feasibility of magnetic recording at 1 Terabit per square inch", IEEE Trans. Magn., Vol. 36, No. 1, pp. 36-42, Jan 2000| journal = IEEE Transactions on Magnetics| date = January 2000| volume = 36| issue = 1| pages = 36–42| doi = 10.1109/20.824422| last1 = Wood| first1 = R.}}</ref><ref>{{cite press release |title=Hitachi achieves nanotechnology milestone for quadrupling terabyte hard drive |publisher=[[Hitachi]] |date=October 15, 2007 |url= http://www.hitachi.com/New/cnews/071015a.html |access-date=1 Sep 2011 }}</ref>
* Future hard disk technologies currently in development include: [[heat-assisted magnetic recording]] (HAMR) and [[microwave-assisted magnetic recording]] (MAMR), which use materials that are stable at much smaller sizes.<ref>{{cite journal| url = https://ieeexplore.ieee.org/document/5257351| title = Y. Shiroishi et al., "Future Options for HDD Storage", IEEE Trans. Magn., Vol. 45, No. 10, pp. 3816-22, Sep. 2009| journal = IEEE Transactions on Magnetics| date = October 2009| volume = 45| issue = 10| pages = 3816–3822| doi = 10.1109/TMAG.2009.2024879| s2cid = 24634675| last1 = Shiroishi| first1 = Y.| last2 = Fukuda| first2 = K.| last3 = Tagawa| first3 = I.| last4 = Iwasaki| first4 = H.| last5 = Takenoiri| first5 = S.| last6 = Tanaka| first6 = H.| last7 = Mutoh| first7 = H.| last8 = Yoshikawa| first8 = N.}}</ref> They require localized heating or microwave excitation before the magnetic orientation of a bit can be changed. [[Bit-patterned recording]] (BPR) avoids the use of fine-grained media and is another possibility.<ref>{{cite magazine |url=https://www.pcmag.com/article2/0,2817,2368023,00.asp |title=Will Toshiba's Bit-Patterned Drives Change the HDD Landscape? |last1=Murray |first1=Matthew |magazine=[[PC Magazine]] |date=2010-08-19 |access-date=21 Aug 2010}}</ref> In addition, magnetic recording technologies based on topological distortions of the magnetization, known as [[skyrmion]]s, have been proposed.<ref>{{Cite journal|last1=Fert|first1=Albert|last2=Cros|first2=Vincent|last3=Sampaio|first3=João|date=2013-03-01|title=Skyrmions on the track|journal=Nature Nanotechnology|language=en|volume=8|issue=3|pages=152–156|doi=10.1038/nnano.2013.29|pmid=23459548|issn=1748-3387|bibcode=2013NatNa...8..152F}}</ref>