Barium ferrite, or Barium hexaferrite, is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

(), sometimes abbreviated BaFe, BaM. This and related ferrite materials are components in

magnetic stripe card The term digital card can refer to a physical item, such as a memory card on a camera, or, increasingly since 2017, to the digital content hosted as a virtual card or cloud card, as a digital virtual representation of a physical card. They shar ...

s and

loudspeaker A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

magnets. BaFe is described as . The centers are ferrimagnetically coupled, and one unit cell of BaM has a net magnetic moment of 40. This area of technology is usually considered to be an application of the related fields of

materials science Materials science is an interdisciplinary field of researching and discovering materials. Materials engineering is an engineering field of finding uses for materials in other fields and industries. The intellectual origins of materials sci ...

and

solid state chemistry Solid-state chemistry, also sometimes referred as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials. It therefore has a strong overlap with solid-state physics, mineralogy, crystallography, ceram ...

. Barium ferrite is a highly magnetic material, has a high packing density, and is a metal

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

. Studies of this material date at least as far back as 1931, and it has found applications in magnetic card strips, speakers, and

magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic ...

s. 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.

Chemical structure

The centers, with a high-spin d configuration, are ferrimagnetically coupled. This area of technology is usually considered to be an application of the related fields of

and

. A related family of industrially useful "hexagonal ferrites" are known, also containing

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

. In contrast to the usual

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , a diminutive form of ''spine,'' in reference to its pointed crystals. Prop ...

structure, these materials feature

hexagonal close-packed In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or Lattice (group), lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fract ...

framework of oxides. Furthermore, some of the oxygen centers are replaced by ions. Formulas for these species include , , and . A one-step hydrothermal process can be used to form crystals of barium ferrite, by mixing

barium chloride Barium chloride is an inorganic compound with the formula . It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flam ...

, ferrous chloride,

potassium nitrate Potassium nitrate is a chemical compound with a sharp, salty, bitter taste and the chemical formula . It is a potassium salt of nitric acid. This salt consists of potassium cations and nitrate anions , and is therefore an alkali metal nit ...

, and

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

with a hydroxide to chloride concentration ratio of 2:1. Nano-particles are prepared from

ferric nitrate Iron(III) nitrate, or ferric nitrate, is the name used for a series of inorganic compounds with the formula Fe(NO3)3.(H2O)n. Most common is the nonahydrate Fe(NO3)3.(H2O)9. The hydrates are all pale colored, water-soluble paramagnetic salts. Hy ...

, barium chloride,

sodium citrate Sodium citrate may refer to any of the sodium salts of citric acid (though most commonly the third): * Monosodium citrate * Disodium citrate * Trisodium citrate The three forms of salt are collectively known by the E number E331. Applications ...

, and sodium hydroxide. The typical preparation, however, is by

calcining Calcination is thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), generally fo ...

barium carbonate Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of ...

with

iron(III) oxide Iron(III) oxide or ferric oxide is the inorganic compound with the formula . It occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when use ...

: : + 6 ->

text Text may refer to: Written word * Text (literary theory) In literary theory, a text is any object that can be "read", whether this object is a work of literature, a street sign, an arrangement of buildings on a city block, or styles of clothi ...

/chem> +

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. Barium ferrite also proved to be resistant to thermal demagnetization, another issue common with long-term storage. The

Curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie ...

is typically around 450 °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 °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.

Chemical properties

Barium ferrites are robust

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

s that are generally stable to moisture and corrosion-resistant. 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.

Mechanical properties

Metal particle A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against non ...

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 nm while Ba-Fe is only 20 nm. So the smallest metal particles are still double the size of the Ba-Fe particles.

Uses

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 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.

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 Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plas ...

, 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.

Tape Data Storage Media

Barium ferrite is used for enterprise level and commodity

linear tape-open Linear Tape-Open (LTO), also known as the LTO Ultrium format, is a magnetic tape data storage technology used for backup, data archiving, and data transfer. It was originally developed in the late 1990s as an open standards alternative to the pro ...

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

Magnetic stripes

ID cards using barium ferrite are made with a magnetic fingerprint that identifies them, allowing readers to self-calibrate.

Natural occurrence

The compound occurs in nature, although is exceedingly rare. It is called barioferrite and is related to pyrometamorphism.

References

{{Barium compounds Barium compounds Ferrites