BASICS: First it is appropriate to understand that there are two types of magnets: permanent magnets and electromagnets. Permanent magnets (or bar magnets) are materials that exhibit the property of magnetism by nature of the material - like the refrigerator magnets most people are familiar with. With that in mind, the remaining discussion will focus on electromagnets.
Magnetism is created when electric current flows through a wire. Even the electricity flowing through your house wiring creates a weak magnetic field. But we generally don't refer to house wiring carrying electric current as a magnet. More practically, electromagnets are created by forming a coil of wire, often referred to as a solenoid. Each turn of the coil contributes a small magnetic field, so when the coil is wound with hundreds or even thousands of turns, the magnetic field contribution of each turn add together, and the result can be a magnetic field stronger than any permanent magnet. No iron is required to produce a magnetic field from a coil of wire, but if iron is used, the effect is such that the magnetic field is focused and concentrated in the iron, so the field strength can be increased where the iron is present. A familiar example from basic science class (if they even have such a thing these days) is the experiment where a bunch of electrical wire is wrapped around an iron nail. When the wire is hooked up to a battery, a magnetic field is produced from current flowing in the wire and gets concentrated in the iron nail, turning the iron nail into a magnet. But keep in mind that not all elecromagnets use iron, since it is not always desirable to concentrate the magnetic field.
Now lets take it a step further. Materials have been discovered years ago that conduct electricity with virtually zero resistance when they are cooled to near absolute zero (-454 F or -273 C), which is so cold it is hard for us hot life forms to comprehend. When coils of wire made up of this material are cooled to a few degrees above absolute zero, they start to superconduct and it is possible to flow hundreds and even thousands of times the electric current through them. This also means that they will produce magnetic fields that are hundreds to thousands of times stronger than a coil of same size ordinary copper wire! This is called a superconducting magnet. If you tried to do this with an ordinary copper wire, it would heat up until it glowed white hot and melted. In the five examples provided at this site, all use superconducting magnet coils that operate at just a few degrees above absolute zero using special cryogenic equipment (not cryonics which is the so called science of freezing people). Some of the examples use iron to concentrate the field, and some do not.
There are many examples of superconducting magnets used for more peacefull applications, not like the ones given in the five categories provided at this site. A widely used example is the MRI (Magnetic Resonance Imaging) magnet, which is used for imaging internal organs of people for medical diagnostic purposes. The figure below is a one type, built by General Atomics in San Diego. They build about 20 per month. In principle, it is a basic superconducting magnet just as described above. By the way, these magnets used to be called NMR magnets which stood for Nuclear Magnetic Resonance imaging magnet. This is in fact a technically accurate description of the device, but no radiation is involved. However, you could never convince the patient of that, so people would always freak out when they had to go inside them. Solution? Just change the name.
That's about as for as we'll go for this lesson. For more information on applications of superconductivity, click here for this web site.
