Ring magnets, named for their round shape with a hole in the middle, are often used in science and medicine.
Magnets produce magnetic fields, or areas where potentially magnetic materials, such as iron, become polarized and attract the magnet. There are two types of magnets: permanent magnets and electromagnets. Permanent magnets have a constant magnetic field, while electromagnets only produce a field when an electric current passes through the coil that is part of their structure. Ring magnets are permanent magnets distinguished by their shape: they are round with a hole in the middle, and because of this shape they are sometimes called string magnets.
A variety of materials are used to create permanent magnets. They are often made from a group of materials called rare earths, which are mixtures of elements, usually neodymium, iron and boron, or samarium and cobalt. Alnico magnets are mixtures of aluminum, nickel and cobalt. There are also weaker magnets made from magnetic materials like iron oxide mixed with non-magnetic materials like plastic or ceramic. The magnetic elements produce the field, while the non-magnetic elements give the shape of the magnet.
However, these materials are not naturally magnetic, they simply have magnetic potential. In the factories where they are made, workers first mold the material into the desired shape and may coat the magnet to make it more colorful. They then pass the object through a strong electromagnet, which induces magnetic properties in the object that remain even after the electromagnet is turned off. If the electromagnet is strong enough, this process will create a permanent magnet.
The magnetization process creates poles on the magnet that are labeled north and south, with each repelling like poles and attracting opposite poles. The location of the northern and southern parts of the magnetic rings depends on how they are polarized; half is always north and the other half is south. Sometimes the magnet splits so that one side of the ring faces north and the other faces south, but different types of polarization can create magnets that split into quarters or eighths. The north and south segments always alternate around the ring.
Ring magnets are most often used in scientific experiments, although they also have medical applications. Some people have implantable cardioverter defibrillators, or ICDs, that automatically shock their hearts if the rhythm develops irregularities. If the devices malfunction, they can deliver unnecessary electrical shocks to patients, leading to irregular rhythms and possibly death. Medical staff sometimes place these magnets on patients’ chests over ICDs to deactivate the devices.