View source for Barium ferrite

{{use dmy dates |date=December 2023}}
{{Chembox
| ImageFile = File:Barium_ferrite_crystal_structure.png
| ImageSize = 
| ImageAlt = 
| ImageCaption =Barium ferrite crystal structure
| IUPACName = 
| OtherNames = 
| Section1={{Chembox Identifiers
  | CASNo = 12047-11-9
  | CASNo_Ref = {{cascite|correct|CAS}}
  | ChemSpiderID = 	17345241
  | EINECS = 234-974-5
  | UNII_Ref = {{fdacite|correct|FDA}}
  | UNII = 4HT629NL8B
  | PubChem = 16217742
  | InChI=1S/Ba.12Fe.19O
  | InChIKey = AJCDFVKYMIUXCR-UHFFFAOYSA-N
  | SMILES = O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Ba]
}}
| Section2={{Chembox Properties
  | Fe=12 |O=19 |Ba=1
  | MolarMass =
  | Appearance = black solid
  | Density = 5.28 g/cm<sup>3</sup>
  | MeltingPtC = 1316
  | BoilingPt = 
  | Solubility = insoluble
}}
| Section3={{Chembox Hazards
  | MainHazards = 
  | FlashPt = 
  | AutoignitionPt =
}}
}}
'''Barium [[Ferrite (magnet)|ferrite]]''', abbreviated BaFe, BaM, is a [[chemical compound]] with the [[chemical formula|formula]] {{chem|Ba|Fe|12|O|19}} ({{nobr|{{chem|Ba|O}} : 6 {{chem|Fe|2|O|3}} }}).<ref name = Pullar /> This and related [[Ferrite (magnet)|ferrite]] materials are components in [[magnetic stripe card]]s and [[loudspeaker]] magnets.

BaFe is described as {{chem|Ba|2+|Fe|3+|12|O|2−|19}}. The {{chem|Fe|3+}} centers are [[Ferrimagnetism|ferrimagnetically]] coupled, and one unit cell of BaM has a net magnetic moment of 40{{math|μ}}{{sub|B}}.<ref name=Cao-Zhao-etal-2015>{{cite journal |last1=Cao |first1=H.B. |last2=Zhao |first2=Z.Y. |last3=Lee |first3=M. |last4=Choi |first4=E.S. |last5=McGuire |first5=M.A. |last6=Sales |first6=B.C. |last7=Zhou |first7=H.D. |last8=Yan |first8=J.-Q. |last9=Mandrus |first9=D.G. |date=2015-06-01 |df=dmy-all |title=High pressure floating zone growth and structural properties of ferrimagnetic quantum paraelectric BaFe12O19 |journal=APL Materials |volume=3 |issue=6 |pages=062512 |doi=10.1063/1.4922934 |doi-access=free |arxiv=1503.02568 |bibcode=2015APLM....3f2512C |s2cid=98312433 }}</ref> This area of technology is usually considered to be an application of the related fields of [[materials science]] and [[solid state chemistry]].

Barium ferrite is a highly [[magnetic material]], has a high packing density,{{clarify|date=August 2017}} and is a metal [[oxide]]. Studies of this material date at least as far back as 1931,<ref>{{cite journal|first1 = Joseph|last1 = Guillissen|first2 = Pierre J.|last2 = van Rysselberghe |year = 1931 |title = Studies on zinc and barium ferrites |journal = [[J. Electrochem. Soc.]] |volume =  59 |issue = 1 |pages = 95–106 |doi = 10.1149/1.3497845| s2cid=97566562 |url = https://dipot.ulb.ac.be/dspace/bitstream/2013/267749/4/b6ad08ac-37da-4ca9-a0ae-1c3670862100.txt}}</ref> and it has found applications in magnetic card strips, speakers, and [[magnetic tape]]s.<ref name = Pullar /> One area in particular it has found success in is long-term data storage; the material is magnetic, resistant to temperature change, corrosion and oxidization.<ref name = ieeeThermalStudy>{{cite journal |first1 = Mark L. |last1 = Watson |first2 = Robert A. |last2 = Beard |first3 = Steven M. |last3 = Kientz |first4 = Timothy W. |last4 = Feebeck |year = 2008 |title = Investigation of Thermal Demagnetization Effects in Data Recorded on Advanced Barium Ferrite Recording Media|journal = [[IEEE Trans. Magn.]] |volume = 44 |issue = 11|pages = 3568–3571|doi = 10.1109/TMAG.2008.2001591 |bibcode = 2008ITM....44.3568W |s2cid = 22303270}}</ref>

==Chemical structure==
The {{chem|Fe|3+}} centers, with a [[Crystal field theory|high-spin]] [[d shell|d]]{{sup|5}} configuration, are [[Ferrimagnetism|ferrimagnetically]] coupled.<ref name=Cao-Zhao-etal-2015/><ref>{{Cite journal |last1=Rowley |first1=S.E. |last2=Chai |first2=Yi-Sheng |last3=Shen |first3=Shi-Peng |last4=Sun |first4=Young |last5=Jones |first5=A.T. |last6=Watts |first6=B.E. |last7=Scott |first7=J.F. |date=2016-05-17 |df=dmy-all |title=Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19 |journal=Scientific Reports |volume=6 |issue=1 |pages=25724 |doi=10.1038/srep25724 |issn=2045-2322 |pmc=4869023 |pmid=27185343 |bibcode=2016NatSR...625724R |lang=en}}</ref> This area of technology is usually considered to be an application of the related fields of [[materials science]] and [[solid state chemistry]].

A related family of industrially useful "hexagonal ferrites" are known, also containing [[barium]].<ref name = Pullar>{{cite journal |first = Robert C. |last = Pullar |year = 2012 |title = Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics |journal = [[Progress in Materials Science]] |volume = 57 |issue = 7 |pages = 1191–1334 |doi = 10.1016/j.pmatsci.2012.04.001 |issn=0079-6425 |url=https://www.sciencedirect.com/science/article/pii/S0079642512000369}}</ref> In contrast to the usual [[spinel]] structure, these materials feature [[hexagonal close-packed]] framework of oxides. Furthermore, some of the oxygen centers are replaced by {{chem|Ba|2+}} ions. Formulas for these species include {{chem|Ba|Fe|12|O|19}}, {{chem|Ba|Fe|15|O|23}}, and {{chem|Ba|Fe|18|O|27}}.<ref>{{cite journal |first1 = Yasumasa |last1 = Goto |first2 = Toshio |last2 = Takada |year = 1960 |title = Phase diagram of the system {{chem|Ba|O}}-{{chem|Fe|2|O|3}} |journal = [[J. Am. Ceram. Soc.]] |volume = 43 |issue = 3 |pages = 150–153 |doi = 10.1111/j.1151-2916.1960.tb14330.x}}</ref>

A one-step hydrothermal process can be used to form crystals of barium ferrite, by mixing [[barium chloride]], [[ferrous chloride]], [[potassium nitrate]], and [[sodium hydroxide]] with a hydroxide to chloride concentration ratio of 2:1. Nano-particles are prepared from [[ferric nitrate]], barium chloride, [[sodium citrate]], and sodium hydroxide.<ref>{{cite book |first = Shahida B. |last = Niazi |year = 2016 |chapter = Solvothermal / hydrothermal synthetic methods for nanomaterials |editor1-first = Sher Bahadar |editor1-last = Khan |editor2-first = Abdullah M. |editor2-last = Asiri |editor3-first = Kalsoom |editor3-last = Akhtar |title = Nanomaterials and their Fascinating Attributes |volume = 1 |series = Development and Prospective Applications of Nanoscience and Nanotechnology |publisher = [[Bentham Science Publishers]] |isbn = 9781681081779 |pages = 181–238 |chapter-url = https://books.google.com/books?id=eKniDQAAQBAJ&pg=PA197 }}</ref> The typical preparation, however, is by [[calcination|calcining]] [[barium carbonate]] with [[iron(III) oxide]]:<ref>{{cite book |first = Carl |last = Heck |year = 1974 |chapter = Ceramic magnet materials (ferrites) |title = Magnetic Materials and Their Applications |publisher = [[Butterworths]] |isbn = 9781483103174 |pages = 291–294 |chapter-url = https://books.google.com/books?id=yvEkBQAAQBAJ&pg=PA291}}</ref>

:[[Barium carbonate|{{chem|Ba|C|O|3}}]]  +  6&nbsp;[[iron(III) oxide|{{chem|Fe|2|O|3}}]]  <chem>->[\text{Δ}]</chem>  {{chem|Ba|Fe|12|O|19}}  +  [[carbon dioxide|{{chem|C|O|2}}]]

==Properties==
Barium ferrite has been considered for long term data storage. The material has proven to be resistant to a number of different environmental stresses, including humidity and corrosion. Because ferrites are already oxidized it can not be oxidized any further. This is one reason ferrites are so resistant to corrosion.<ref name=Japan>{{cite journal |first1 = Chisato |last1 = Okazaki |first2 = Saburo |last2 = Mori |first3 = Fumikazu |last3 = Kanamaru |title = Magnetic and crystallographical properties of hexagonal barium mono-ferrite, {{chem|Ba|O}}•{{chem|Fe|2|O|3}} |journal = [[J. Phys. Soc. Jpn.]] |year = 1961 |volume = 16 |issue = 3 |page = 119 |doi = 10.1143/JPSJ.16.119}}</ref> Barium ferrite also proved to be resistant to thermal demagnetization, another issue common with long-term storage.<ref name= ieeeThermalStudy /> The [[Curie temperature]] is typically around 450&nbsp;°C (723K).

When barium ferrite magnets increase in temperature, their high intrinsic coercivity improves, this is what makes it more resistant to thermal demagnetization. Ferrite magnets are the only type of magnets that become substantially more resistant to demagnetization as temperature increases. This characteristic of barium ferrite makes it a popular choice in motor and generator designs and also in loudspeaker applications. Ferrite magnets can be used in temperatures up to 300&nbsp;°C, which makes it a perfect to be used in the applications mentioned above. Ferrite magnets are extremely good insulators and don't allow any electrical current to flow through them and they are brittle which shows their ceramic characteristics. Ferrite magnets also have good machining properties, which allows for the material to be cut in many shapes and sizes.<ref>{{cite web |title = Characteristics of ferrite magnets |url = http://e-magnetsuk.com/ferrite_magnets/characteristics.aspx |website = e-Magnets UK |access-date = 8 December 2013 <!-- This ref was obtained from http://www.ferrite-info.com/characteristics.aspx on 8 December 2013. At some point when the publisher company was renamed, it was moved to the e-magnetsuk.com address. Comparing the content to the archive.org version shows no change, so older access-date is retained even though new address was accessed on 13 August 2017 --> }}</ref>

===Chemical properties===
Barium ferrites are robust [[ceramic]]s that are generally stable to moisture and corrosion-resistant.<ref name=Japan/> Ba‑Fe ferrite is an oxide, so it does not break down due to oxidation as much as a metal alloy might; giving Ba‑Fe a much greater life expectancy.<ref name=ieeeThermalStudy/>

===Mechanical properties===
[[Metal particle]]s have been used to store data on tapes and magnetic strips but they have reached their limit for high capacity data storage. In order to increase their capacity by (25×) on data tape the metal particles had to increase the tape length by (45%) and track density by over (500%) which made it necessary to reduce the size of the individual particles. As the particles were reduced in size, the passivizing coating needed to prevent the oxidation and deterioration of the metal particles had to become thicker. This presented a problem for as the passivation coating got thicker it became harder to achieve an acceptable signal to noise ratio.

Barium ferrite completely out classes metal particles, mostly because Ba‑Fe is already in its oxidized state and so is not restricted in its size by a protective coating. Also due to its hexagonal pattern it is easier to organize compared to the unorganized rod like metal particles. Another factor is the difference in the size of the particles, in metal particles the size ranges from 40 to 100&nbsp;nm while Ba-Fe is only 20&nbsp;nm. So the smallest metal particles are still double the size of the Ba-Fe particles.<ref>{{cite web |title = Barium ferrite: Overview |publisher = [[Fujifilm]] |url = http://www.fujifilmusa.com/products/tape_data_storage/innovations/barium_ferrite/index.html |url-status = dead |access-date = August 13, 2017 |archive-url = https://web.archive.org/web/20170813055029/http://www.fujifilmusa.com/products/tape_data_storage/innovations/barium_ferrite/index.html |archive-date = August 13, 2017}}</ref>

== Uses ==
[[File:Dds tape drive 01.jpg|thumbnail|Barium Ferrite is used in tape drives and floppy disks.]]

Barium ferrite is used in recording media, permanent magnets, and magnetic stripe cards (credit cards, hotel keys, ID cards). Due to the stability of the material, it is able to be greatly reduced in size, making the packing density much greater. Earlier media devices utilized doped [[Acicular (crystal habit)|acicular]] oxide materials to yield the coercivity values necessary to record. In recent decades, barium ferrite has replaced acicular oxides; without any dopants, the acicular oxides produce very low coercivity values, making the material very magnetically soft, while barium ferrite's higher coercivity levels make the material magnetically hard and thus a superior choice for recording materials.

=== Magnetic stripes ===
ID cards using barium ferrite are made with a magnetic fingerprint that identifies them, allowing readers to self-calibrate.<ref>{{cite book |first = Gerard |last = Honey |year = 2000 |chapter = Card-based identification systems |title = Electronic Access Control |publisher = [[Elsevier#Imprints|Newnes]] |isbn = 9780750644730 |pages = 47–55 |chapter-url = https://books.google.com/books?id=UIlg6kdz1skC&pg=PA49}}</ref>

===Speaker magnets===
Barium ferrite is a common material for speaker magnets. The materials can be formed into almost any shape and size using a process called [[sintering]], whereby powdered barium ferrite is pressed into a mold, and then heated until it fuses together. The barium ferrite turns into a solid block while still retaining its magnetic properties. The magnets have an excellent resistance to demagnetization, allowing them to still be useful in speaker units over a long period of time.<ref>{{cite web |title = Hard ferrite (ceramic) magnets |publisher = Magnaworks Technology |url = http://www.magnaworkstechnology.com/ceramic-1.html |access-date = December 8, 2013 |url-status = dead <!-- Access date of December 8, 2013 is retained. This date relates to the address http://www.magnaworkstechnology.com/ceramic_magnets.shtml which was archived on 1 January 2014 to https://web.archive.org/web/20140101004754/http://www.magnaworkstechnology.com/ceramic_magnets.shtml. Ref target changed to a new location, http://www.magnaworkstechnology.com/ceramic-1.html, on 13 August 2017, which is live and appears to carry the same content as the old version. --> |archive-url = https://web.archive.org/web/20181020080711/http://www.magnaworkstechnology.com/ceramic-1.html |archive-date = October 20, 2018 }}</ref>

===Tape Data Storage Media===
Barium ferrite is used for enterprise level<ref name=fujifilm-barium-ferrite>{{cite web |title=Barium ferrite: Overview |department=Data storage |series=Fujifilm Technologies |publisher=[[Fujifilm]] |place=United States |url=https://www.fujifilm.com/us/en/business/data-storage/fujifilm-technologies/barium-ferrite}}</ref> and commodity [[Linear Tape-Open|linear tape-open]] (LTO) tape storage media. Because of its high density, barium ferrite has led to data capacity improvements in both enterprise and LTO tapes over prior metal particle (MP) media technology.<ref>{{cite press release |title = FujiFilm barium-ferrite magnetic tape establishes world record in data density: 29.5&nbsp;billion bits per square inch |date = 22 January 2010 |publisher = [[Fujifilm]] |url = https://www.fujifilm.eu/de/presse/artikel/fujifilm-barium-ferrite-magnetic-tape-establishes-world-record-in-data-density-295-billion-bits-per-square-inch |access-date = 2020-10-12 |url-status = dead |archive-url = https://web.archive.org/web/20201019093053/https://www.fujifilm.eu/de/presse/artikel/fujifilm-barium-ferrite-magnetic-tape-establishes-world-record-in-data-density-295-billion-bits-per-square-inch|archive-date = 2020-10-19}}</ref>

Developments in the field have also resulted in the reduction of the size of Ba-Fe particles to about 20&nbsp;nm. This contrasts with metal particle technology, which has problems shrinking the particles past 100&nbsp;nm.<ref name=ieeeThermalStudy/> Barium ferrite has better packing properties than most other metal particles because of the distinctive shape of the particles.<ref name=ieeeThermalStudy/> This leads to better control over magnetic orientation and improved signal-to-noise characteristics.<ref name=fujifilm-barium-ferrite/>

==Natural occurrence==
The compound occurs in nature, although is exceedingly rare. It is called barioferrite and is related to pyrometamorphism.<ref>{{cite web |title=Barioferrite |website=mindat.org |url=https://www.mindat.org/min-39567.html}}</ref><ref>{{cite web |title=List of Minerals |website=ima-mineralogy.org |url=https://www.ima-mineralogy.org/Minlist.htm |date=21 March 2011}}</ref>

==References==
{{reflist|25em}}

{{Barium compounds}}

[[Category:Barium compounds]]
[[Category:Ferrites]]