Neodymium magnets, also known as NdFeB or rare-earth magnets, are made from an alloy of neodymium, iron and boron. This is the alloy from which magnets in microphones, professional loudspeakers and computer hard drives are made. The magnets are made by sintering, a method of welding tiny particles of metal together by the application of heat. Any ‘holes’ present in a rare-earth magnet have not been drilled. The sintered mixture of metal was poured into a mold at the time of the magnet’s manufacture. Because of this, the magnets have a ‘ceramic’ quality. They are fragile and should be handled with care.
The magnets should not be machined or drilled, because drilling can cause them to shatter and break. The drilling activity produces a powder of tiny particles of metal, which is flammable. The heat produced by the friction of the drilling can also ignite the powder, and burn or melt anything nearby. There are instances of subjects who tried to drill through a neodymium magnet, and found their drill bits melted.
Ignited rare-earth particles burn intensely; all metallic particles do. Iron particles, for instance, burn in a spectacular blaze. This is because ignited metals form oxides with oxygen from the air. Increase the number of burning particles, in this case the tiny fragments of shattered magnet, and you increase the number of ‘fires’ taking place. The heat of these fires will ignite any other nearby particles, thus creating a small inferno.
Metallic oxides are airborne and can be inhaled, as demonstrated by the ‘metal fume fever’ that workers in metallurgy are prone to. The symptoms are non-specific but often mimic illnesses like pneumonia and influenza. Particles of the magnet can end up on the skin, and can be ingested and find their way into food and drink. The toxic qualities of neodymium are unknown as yet.
Cutting or drilling a rare-earth magnet in half will not provide the subject with two magnets, but two pieces of metal that are no longer magnetic. The reason for magnetism in metal is the alignment of their magnetic dipoles or ‘fields’ in one direction. Heat provides energy to the dipoles of the metals so that they can break free of their original bonds and align in other, different directions.
When machining or drilling a neodymium magnet, it is possible that the build-up of heat may cause it to demagnetize. However, it is also likely that the actual drilling may be the cause. Jarring and hammering a magnet have the same effect on its dipoles as heat does. Unless you are a professional or have a significant amount of experience in ceramics, it is not recommended that you drill or machine your rare-earth magnet because of the reasons listed above.