Barium ferrite

Barium ferrite, abbreviated BaFe, BaM, is the chemical compound with the formula BaFe2O4. This and related ferrite materials are components in magnetic stripe cards and loudspeaker magnets. BaFe is described as Ba2+(Fe3+)2(O2−)4. The Fe3+ centers are ferromagnetically coupled.[1] This area of technology is usually considered to be an application of the related fields of materials science and solid state chemistry.

Background

Barium ferrite (BaFe) is a highly magnetic material, has a high packing density, and is a metal oxide. It has been used regularly in studies dating as far back as 1931,[2] however has found popularity recently with its use in magnetic card strips, speakers, and magnetic tapes. One area in particular it has found success in is long-term data storage; material is magnetic and resistant to temperature, corrosion, and oxidization.[3] Barium comes from the Greek word barys, which means "heavy". Iron (Fe) was originally called ferrum, which is a Latin name meaning "holy metal". The word "iron" comes from the Anglo-Saxon word iren.

Chemical Structure

The Fe3+ centers, with a high-spin d5 configuration, are ferromagnetically coupled.[1] 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 the oxygen centers are replaced by Ba2+ ions. Formulas for these species include BaFe12O19, BaFe15O23, and BaFe18O27.[4] Thus, BaFe12O19 is related to Fe12O20, with the empirical formula Fe3O4, i.e. magnetite.[5]

Properties

Recent development has focused on the use of Barium Ferrite as a long term data storage option. 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.[6] Barium ferrite also proved to be resistant to thermal demagnetization, another issue common with long term storage.[3] 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 actually become noticeably more resistant to demagnetization when they get hotter. 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 degrees 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.[7]

Chemical Properties

Barium ferrites are robust ceramics that are generally stable to moisture and corrosion-resistant.[6] BaFe is also an oxide so it does not break down due to oxidation as much as a metal alloy might; giving BaFe a much greater life expectancy.[3]

Mechanical Properties

Metal particles (MP) 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 (25x) on data tape the MP 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 where reduced in size the passivizing coating needed to prevent the oxidation and deterioration of the MP 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 MP, mostly because BaFe 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 MP. Another factor is the difference in the size of the particles, in MP the size ranges from 40-100 nm while the BaFe is only 20 nm. So the smallest MP particle is still double the size of the BaFe particles.[8]

Applications

Barium Ferrite was used in tape drives and floppy disks, among other things.

Barium ferrite is a very applicable material used in many industry fields in today's day and age. The material is seen around the world in applications such as recording items such as tapes and other media devices, permanent magnets, and also 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. In the late media devices, acicular oxides were used which produced the coercivity values necessary to record. Although in the past few decades barium ferrite has replaced the acicular oxides; without any dopants, the acicular oxides produce very low coercivity values, making the material very magnetically soft. The barium ferrite which has recently taken the oxide's place produces much higher coercivity levels which make the material magnetically hard, therefore making the ferrite better for recording materials.

Barcode

As talked about earlier, these ID cards and their readers are implanted with a unique pattern of barium ferrite. The scanner is able to identify the card by the small reader that is implanted with the magnetic barium ferrite pattern and this recognizes the pattern that is also found in the cards barcode.[9]

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.[10]

Linear Tape-Open

Barium ferrite has found to be a unique storage medium for Linear Tape-Open (LTO) storage. Until just recently, the medium for storage in LTO options has been Metal particles (MP). Barium ferrite has been paving the way to the future of LTO tapes because of its high packing density; increases in packing density results in a greater surface area that data can be recorded on.[11]

Developments in the field have also resulted in the a reduction in the size of BaFe particles to about 20 nm. This is in stark contrast to MP technology, which has started to fade away because of problems shrinking the particles past 100 nm.[3]

The shape is also another concern. Metal Particles are often more of a cylinder and can’t be packed or stacked very well. Barium ferrite has much better properties. BaFe can be reduced to a much smaller size and a greater packing density because of its circular structure and can be stacked a lot better.[3]

References

  1. 1 2 Shriver, D. F.; Atkins, P. W.; Overton, T. L.; Rourke, J. P.; Weller, M. T.; Armstrong, F. A. (2006). Inorganic Chemistry. New York: W. H. Freeman. ISBN 0-7167-4878-9.
  2. ↑ Joseph Guillissenb and Pierre J. Van Rysselberghe (1931). "Studies on Zinc and Barium Ferrites". The Electrochemical Society 59 (1): 95–106. doi:10.1149/1.3497845.
  3. 1 2 3 4 5 Mark L. Watson, Robert A. Beard, Steven M. Kientz, and Timothy W. Feebeck (2008). "Investigation of Thermal Demagnetization Effects in Data Recorded on Advanced Barium Ferrite Recording Media". IEEE TRANSACTIONS ON MAGNETICS 44 (11): 3568–3571.
  4. ↑ Y. Goto, T. Takada (1960). "Phase Diagram of the System BaO-Fe2O3". Journal of the American Ceramic Society 43 (3): 150–153. doi:10.1111/j.1151-2916.1960.tb14330.x.
  5. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  6. 1 2 C. Okazaki, S. Mori, F. Kanamaru (1961). "Magnetic and Crystallographical Properties of Hexagonal Barium Mono-Ferrite, BaO·Fe2O3". Journal of the Physical Society of Japan 16 (3): 119–119. doi:10.1143/JPSJ.16.119.
  7. ↑ "Characteristics of Ferrite Magnets". Ferrite Magnets- An Expert Information source. Retrieved 12/8/13. Check date values in: |access-date= (help)
  8. ↑ http://www.fujifilmusa.com/products/tape_data_storage/innovations/barium_ferrite/index.html
  9. ↑ 2013 Secura Key, a Division of Soundcraft, Inc
  10. ↑ "Hard Ferrite (Ceramic) Magnets". Magnaworks Technology. Retrieved December 8, 2013.
  11. ↑ "FUJIFILM BARIUM-FERRITE MAGNETIC TAPE ESTABLISHES WORLD RECORD IN DATA DENSITY: 29.5 BILLION BITS PER SQUARE INCH". 2010. Retrieved 8 December 2013.
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