Barium ferrite

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 materials science and solid state chemistry. A related family of industrially useful "hexagonal ferrites" are known, also containing barium. 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 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, 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. The typical preparation, however, is by calcining barium carbonate with iron(III) oxide: :Barium carbonate| + 6 iron(III) oxide| ->[\text{Δ}] + carbon dioxide| ==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. Chemical properties Barium ferrites are robust ceramics that are generally stable to moisture and corrosion-resistant. == 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, 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 (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. ==Natural occurrence==

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