Magnet corrosion created problems for many applications.

In the past, neodymium magnets could not be used in some applications for fear of corrosion, even though they are the strongest magnets available. Large amounts of iron and the powder metal process used to create neodymium iron boron magnets make them highly susceptible to corrosion. There are also a multitude of other uses where the strongest magnet available is most desirable but corrosion issues have prevented their use, including medical implants and cow magnets.