How Magnets Work

Many of today's electronic devices require magnets to function. This reliance on magnets is relatively recent, primarily because most modern devices require magnets that are stronger than the ones found in nature. Lodestone, a form of magnetite, is the strongest naturally occurring magnet. It can attract small objects, like paper clips and staples.

By the 12th century, people had discovered that they could use lodestone to magnetize pieces of iron, creating a compass. Repeatedly rubbing lodestone along an iron needle in one direction magnetized the needle. It would then align itself in a north-south direction when suspended. Eventually, scientist William Gilbert explained that this north-south alignment of magnetized needles was due to Earth behaving like an enormous magnet with north and south poles.

A compass needle isn't nearly as strong as many of the permanent magnets used today. But the physical process that magnetizes compass needles and chunks of neodymium alloy is essentially the same. It relies on microscopic regions known as magnetic domains, which are part of the physical structure of ferromagnetic materials, like iron, cobalt and nickel. Each domain is essentially a tiny, self-contained magnet with a north and south pole. In an unmagnetized ferromagnetic material, each domain's north pole points in a random direction. Magnetic domains that are oriented in opposite directions cancel one another out, so the material does not produce a net magnetic field.

In magnets, on the other hand, most or all the magnetic domains point in the same direction. Rather than canceling one another out, the microscopic magnetic fields combine to create one large magnetic field. The more domains point in the same direction, the stronger the overall field. Each domain's magnetic field extends from its north pole into the south pole of the domain ahead of it.

This explains why breaking a magnet in half creates two smaller magnets with north and south poles. It also explains why opposite poles attract — the field lines leave the north pole of one magnet and naturally enter the south pole of another, essentially creating one larger magnet. Like poles repel each other because their lines of force are traveling in opposite directions, clashing with each other rather than moving together.

To make a permanent magnet, all you have to do is encourage the magnetic domains in a piece of metal to point in the same direction. That's what happens when you rub a needle with a magnet — the exposure to the magnetic field encourages the domains to align. Other ways to align magnetic domains in a piece of metal include:

Two of these methods are among scientific theories about how lodestone forms in nature. Some scientists speculate magnetite becomes magnetic when struck by lightning. Others theorize that pieces of magnetite became magnets when Earth was first formed. The domains aligned with Earth's magnetic field while iron oxide was molten and flexible.

The most common method of making magnets today involves placing metal in a magnetic field. The field exerts torque on the material, encouraging the domains to align. There's a slight delay, known as hysteresis, between the application of the field and the change in domains; it takes a few moments for the domains to start to move. Here's what happens:

The resulting magnet's strength depends on the amount of force used to move the domains. Its permanence, or retentivity, depends on how difficult it was to encourage the domains to align. Materials that are hard to magnetize generally retain their magnetism for longer periods, while materials that are easy to magnetize often revert to their original nonmagnetic state.

You can reduce a magnet's strength or demagnetize it entirely by exposing it to a magnetic field that is aligned in the opposite direction. You can also demagnetize a material by heating it above its Curie point, or the temperature at which an object's magnetic properties change. The heat distorts the material and excites the magnetic particles, causing the domains to fall out of alignment.

If you've read How Electromagnets Work, you know that an electrical current moving through a wire creates a magnetic field. Moving electrical charges are responsible for the magnetic field in permanent magnets as well. But a magnet's field doesn't come from a large current traveling through a wire — it comes from the movement of electrons.

Many people imagine electrons as tiny particles that orbit an atom's nucleus the way planets orbit a sun. As quantum physicists currently explain it, the movement of electrons is a little more complicated than that. Essentially, electrons fill an atom's shell-like orbitals, where they behave as both particles and waves. The electrons have a charge and a mass, as well as a movement that physicists describe as spin in an upward or downward direction.

Generally, electrons fill the atom's orbitals in pairs. If one of the electrons in a pair spins upward, the other spins downward. It's impossible for both of the electrons in a pair to spin in the same direction. This is part of a quantum-mechanical principle known as the Pauli Exclusion Principle.

Even though an atom's electrons don't move very far, their movement is enough to create a tiny magnetic field. Since paired electrons spin in opposite directions, their magnetic fields cancel one another out. Atoms of ferromagnetic elements, on the other hand, have several unpaired electrons that have the same spin. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, these electrons have an orbital magnetic moment. The magnetic moment is a vector — it has a magnitude and a direction. It's related to both the magnetic field strength and the torque that the field exerts. A whole magnet's magnetic moments come from the moments of all of its atoms.

In metals like iron, the orbital magnetic moment encourages nearby atoms to align along the same north-south field lines. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms with parallel orbital spin line up within the crystal structure. This forms the magnetic domains discussed in the previous section.

You may have noticed that the materials that make good magnets are the same as the materials magnets attract. This is because magnets attract materials that have unpaired electrons that spin in the same direction. In other words, the quality that turns a metal into a magnet also attracts the metal to magnets. Many other elements are diamagnetic — their unpaired atoms create a field that weakly repels a magnet. A few materials don't react with magnets at all.

This explanation and its underlying quantum physics are fairly complicated, and without them the idea of magnetic attraction can be mystifying. So it's not surprising that people have viewed magnetic materials with suspicion for much of history.

Every time you use a computer, you're using magnets. If your home has a doorbell, it probably uses an electromagnet to drive a noisemaker. Magnets are also vital components in CRT televisions, speakers, microphones, generators, transformers, electric motors, burglar alarms, cassette tapes, compasses and car speedometers.

In addition to their practical uses, magnets have numerous amazing properties. They can induce current in wire and supply torque for electric motors. Maglev trains use magnetic propulsion to travel at high speeds, and magnetic fluids help fill rocket engines with fuel.

Earth's magnetic field, known as the magnetosphere, protects it from the solar wind. According to Wired magazine, some people even implant tiny neodymium magnets in their fingers, allowing them to detect electromagnetic fields.

Magnetic resonance imaging (MRI) machines use magnetic fields to allow doctors to examine patients' internal organs. Doctors also use pulsed electromagnetic fields to treat broken bones that have not healed correctly. This method, approved by the United States Food and Drug Administration in the 1980s, can mend bones that have not responded to other treatment. Similar pulses of electromagnetic energy may help prevent bone and muscle loss in astronauts who are in microgravity environments for extended periods.

Magnets can also protect the health of animals. Cows are susceptible to a condition called traumatic reticulopericarditis, or hardware disease, which comes from swallowing metal objects. Swallowed objects can puncture a cow's stomach and damage its diaphragm or heart. Magnets are instrumental to preventing this condition.

One practice involves passing a magnet over the cows' food to remove metal objects. Another is to feed magnets to the cows. Long, narrow alnico magnets, known as cow magnets, can attract pieces of metal and help prevent them from injuring the cow's stomach.

People, on the other hand, should never eat magnets, since they can stick together through a person's intestinal walls, blocking blood flow and killing tissue. In humans, swallowed magnets often require surgery to remove.

Some people advocate the use of magnet therapy to treat a wide variety of diseases and conditions. According to practitioners, magnetic insoles, bracelets, necklaces, mattress pads and pillows can cure or alleviate everything from arthritis to cancer. Some advocates also suggest that consuming magnetized drinking water can treat or prevent various ailments.

Proponents offer several explanations for how this works. One is that the magnet attracts the iron found in hemoglobin in the blood, improving circulation to a specific area. Another is that the magnetic field somehow changes the structure of nearby cells.

However, scientific studies have not confirmed that the use of static magnets has any effect on pain or illness. Clinical trials suggest that the positive benefits attributed to magnets may actually come from the passage of time, additional cushioning in magnetic insoles or the placebo effect. In addition, drinking water does not typically contain elements that can be magnetized, making the idea of magnetic drinking water questionable.