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A Brief History of Permanent Magnets
This article is intended to be a broad, helpful introduction to the history of magnets, as well as an overview of the different kinds of magnets that exist and their relative strengths. It will likely never be complete because of the immense amount of information available on the subject, because of the ever-changing state of the industry and because, after a certain point, the more detail an article provides, the less helpful it will be to most audiences trying to find specific information or a general overview. We will try to update the article as often as is found to be necessary. If you find omissions or errors, feel free to email us at customerservice@ordersofmagnetude.com
| Naturally Occurring / Steel Magnets | ||||||||
|---|---|---|---|---|---|---|---|---|
| Magnet TypeType | Approximate Date Discovered or Synthesized | History / InformationInfo. | Approximate StrengthG | |||||
| The Earth | Prehistory | Weak magnetic field generated by liquid iron convection currents in the earth (Dynamo Theory). The magnetic field has been used for orientation since the 11th century and for navigation since the 12th century. | 0.25 – 0.65 gauss | |||||
| Lode Stone / Naturally Occurring Steel | Prehistory | Lodestones are naturally magnetized deposits of iron oxide (also called magnetite). Vague experimentation and much superstition surrounded lodestones until 1600 when William Gilbert published “De Magnete”. Afterwards it was known that goat’s blood does not increase a magnet’s power, and that capping them (or arming them) with soft iron does.
It was also known for centuries that steel was better than iron for making magnets, but since steel’s chemical composition was not known until the late 1700s, steel, and therefore steel magnets, remained expensive and difficult to produce. |
0.1 – 5.0 gauss | |||||
| Steels of various compositions | Late 1700s – 1920s | Steel magnets were the strongest magnets as soon as carbon steel was able to be reliably produced. The strength of magnets progressed with the addition of various metals to the steel: tungsten in the 1880s, chromium in the 1920s and cobalt in the 1920s. | Up to 200 gauss | |||||
| Composite Magnets | ||||||||
| Magnet TypeType | Approximate Date Discovered or Synthesized | History / InformationInfo. | Approximate StrengthG | |||||
| Alnico | 1930s | Aluminum nickel cobalt, ~50% iron. Alnico magnets have high operating temperatures, they are fairly inexpensive and are very stable. | 400 – 1500 gauss | |||||
| Ferrite | 1930s – 1950s | Invented by researchers at the Tokyo Institute of Technology in the 1930s. Introduced to market in the 1950s. Very inexpensive. On the weak side. Plasticized versions found in refrigerator magnets. | ~3500 gauss | |||||
| Bismanol | 1960s | Synthesized at the United States Naval Ordinance Laboratory (Described in a paper as early as 1953). Soon replaced by neodymium magnets as neodymium magnets are stronger and are less expensive to produce. | ~5.3 megagauss | |||||
| Rare Earth Magnets | ||||||||
| Magnet TypeType | Approximate Date Discovered or Synthesized | History / InformationInfo. | Approximate StrengthG | |||||
| Samarium Cobalt | 1970s | Higher temperature rating and more resistant to demagnetization than Neodymium Iron Boron. However, they are up to 100x as expensive as NIB magnets. | 16-32 megagauss | |||||
| Neodymium Iron Boron | 1980s | Require coating to prevent corrosion. React adversely in atmospheres of hydrogen. | ~64 megagauss | |||||