The most powerful type of magnet is a neodymium alloy, NdFeB, first created in 1982. It is a permanent magnet, with the alloy is composed of equal measure of neodymium, iron and boron. These neodymium rare earth magnets have been a successful alternative to samarium-cobalt magnets. Neodymium Rare Earth Magnets.
Not only do neodymium magnets have strong magnetic charge density – they also possess a high level of coercivity. This helps them to strongly retain their magnetism, at higher temperatures. However at very low temperatures, they are more prone to lose their magnetism. Still, these strong and small magnets are today found in motors, guitars, speakers and MRI scanners- all taking advantage of that high charge magnetic density.
In order to make these magnets, there are 2 approaches that can be taken. The bonded magnet process uses a melt spinning technique. This requires the rapid cooling and heating of the NdFeB alloy, such that a strip of it liquefies and solidifies in quick succession. This method allows the production of finer, smaller magnets. The other approach is the sintered magnet process. This involves producing a powder of the alloy, and then heating it until the particles adhere. Sintered magnets are less robust, and are liable to corrode. But this problem is reduced by coating the magnet in copper or nickel.
The progress in producing ever smaller and more reliable neodymium rare earth magnets has meant this alloy has supplanted the samarium-cobalt magnet, for many higher end and demanding, applications. Samarium-cobalt magnets are still produced in large quantities, but with the greater utility of neodymium magnets, they may over-take their predecessor magnets.