Neodymium is the most powerful permanent magnetic material of which scientists are currently aware. It is also affordable, making it suitable for myriad applications. The chemical composition of a neodymium magnet is Nd2Fe14B, which is two atoms of neodymium, 14 iron atoms, and one boron atom. They are rare-earth magnets, in contrast to conventional ferrite and ceramic magnets, which means that they contain atoms from either the lanthanide or actinide series in the periodic table.
Magnets made with neodymium are the strongest of the rare-earth magnets. Their strength is often given in terms of its gauss rating; depending on their shape and grade, this type of magnet may rate 13,500 gauss or more, although a small one usually rates about 2,000 gauss. By comparison, a refrigerator magnet rates about 50 gauss.
Because they are inexpensive, these magnets are used quite frequently in industry and among hobbyists and dabblers. For example, every computer hard drive has a small neodymium magnet which helps direct the needle that reads data. They can also be found in high-end speakers and science classrooms around the world.
One of the only downsides is that its magnetic field loses some intensity when temperatures are too high. This precludes their use in electronics applications in which a lot of heat is generated. There are versions of the neodymium magnet that perform better under higher temperatures, but in these cases strength must be sacrificed.
Neodymium magnets are incredibly strong; one the size of a US quarter (about 1 inch (24.26 mm) in diameter) can suspend a piece of iron weighing dozens of pounds (kilograms). Two snapping together at the wrong angle can pinch the skin and draw blood. Larger neodymium magnets can be extremely dangerous, wiping credit cards, sending metallic objects flying, and potentially breaking bones if used without care.
For all their danger, neodymium magnets can be used in numerous fun and educational projects. Ferrofluid and magnetic viewing film are commonly used to view magnetic field lines in a physical medium. Carefully arranged neodymium magnets can cause diamagnetic levitation, a peculiar phenomenon that can even levitate live objects such as some frogs. If someone tries to drag one along a non-magnetic conductive surface such as aluminum, it will engage in "magnetic breaking" and be extremely difficult to move. Due to their incredible strength, however, their use is best left to cautious adults.