From lodestones to rare earth magnets, explore the captivating history and diverse range of permanent magnets used in modern technology.
The word – magnet is always related the concept of attraction. In the physical world, it’s a force where two objects pulling towards each other, which we refer to as magnetic force. Abstractly, a magnet can be a person, a thing or a place that is attractive to another person. Just like something may lose its shine or someone his charm over time, however, magnets may also lose its magnetism. That’s where permanent magnets make a difference.
By definition, a permanent magnet is a magnet that never loses its magnetic strength. The first permanent magnet in history is called a loadstone, which is a naturally magnetized rock mainly composed of Fe3O4.
In the modern history, the first permanent magnet ever developed and commercially used is called AlNiCo. AlNiCo was developed in the early 1930s and was then used in military electronic applications during World War II. AlNiCo magnets are divided into cast AlNiCo and sintered AlNiCo. Alnico offers high magnetic field. But it has a low coercive force, which mean it can be easily demagnetized.
In the 1960s, hard ferrite or ceramic magnet was developed and quickly gained popularity in the world industry. It is a low-cost magnetic material made primarily of strontium carbonate and iron oxide (Fe2O3). Due to its good resistance to demagnetization and excellent corrosion resistance, ceramic magnets gained its market very quickly. Nowadays, if measuring by weight, over 70% of the magnets commercially used are hard ferrite/ceramic magnets.
A few years later, something called rare earth magnet was developed. It was Samarium-Cobalt that opened the era of rare earth magnets. This magnetic material has two series: SmCo5 and Sm2Co17 according to composition. In addition to their excellent magnetic strength, they are able to withstand high temperature.
In the early 1980s, a brand-new rare earth magnet called neodymium magnet (NdFeB) was independently developed by Japanese and American. NdFeB magnets exhibit much stronger magnetic flux than any other permanent magnets commericially available. It enables miniaturization in design and introduces more possibilities in modern technology.
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