The Mechanics of Magnetism

Most people are familiar with the fact that magnets attract certain metals and possess north and south poles. Opposing poles draw together, while similar poles push away from one another. Magnetism, along with gravity and the strong and weak atomic forces, is part of the four fundamental forces of the universe.

But none of these details address the fundamental question: What exactly causes a magnet to adhere to specific metals? Why don’t they stick to other types of metal? Why do they attract or repel each other depending on how they are positioned? And what makes neodymium magnets so much stronger than the ceramic magnets we used to play with as kids?

To grasp the answers to these questions, it's important to start with a basic understanding of what a magnet is. Magnets are objects that generate magnetic fields and draw metals such as iron, nickel, and cobalt. The lines of force within the magnetic field flow outward from the magnet's north pole and return through the south pole. Permanent or hard magnets create their own magnetic field continuously. Temporary or soft magnets only produce magnetic fields when they are near a magnetic field, and briefly, even after leaving the field. Electromagnets generate magnetic fields exclusively when electricity moves through their wire coils.

Because electrons and protons act as tiny magnets, every material has some magnetic property. However, in most substances, the opposing spins of electrons cancel out the atom’s magnetic characteristics. Metals are the most widely used materials for making magnets. While some magnets are created from basic metals, alloys—combinations of different metals—can produce magnets with varied strengths. For instance:

How Magnets are Made: The Fundamentals

Modern electronic devices often depend on magnets for functionality. This dependence is relatively recent, mainly because many contemporary gadgets require magnets that are stronger than those found in nature. Lodestone, a type of magnetite, is the strongest natural magnet. It has the ability to attract small items like paper clips and staples.

By the 12th century, humans discovered that rubbing lodestone against iron could magnetize it, leading to the creation of the compass. Repeatedly stroking a lodestone along an iron needle in one direction would magnetize the needle, causing it to align itself north-south when suspended. Later, scientist William Gilbert explained that this north-south alignment was due to Earth acting as a giant magnet with its own north and south poles.

While a compass needle is far weaker than the powerful magnets used today, the magnetization process for both compass needles and neodymium alloy remains essentially the same. It involves microscopic regions known as magnetic domains, which are part of the structure of ferromagnetic materials like iron, cobalt, and nickel. Each domain functions as a small, self-contained magnet with its own north and south poles. In an unmagnetized ferromagnetic material, the domains are randomly oriented, and the opposing directions of the magnetic fields cancel each other out, leaving the material without a net magnetic field.

In magnets, however, most or all of the magnetic domains are aligned in the same direction. Instead of canceling each other out, the individual magnetic fields combine to form one large magnetic field. The more domains that point in the same direction, the stronger the resulting field becomes. The magnetic field of each domain extends from its north pole to the south pole of the adjacent domain.

This illustrates why cutting a magnet in half results in two smaller magnets, each with a north and south pole. It also clarifies why opposite poles attract — the field lines leave the north pole of one magnet and naturally enter the south pole of another, thus creating one larger magnet. Like poles repel because their force lines move in opposite directions, repelling each other rather than merging.

Making Magnets: The Details

To create a permanent magnet, all you need to do is align the magnetic domains in a piece of metal in the same direction. This occurs when you rub a needle with a magnet — the magnetic field exposure encourages the domains to align. Other methods for aligning the magnetic domains in metal include:

Two of these methods are proposed in scientific theories about the natural formation of lodestone. Some scientists suggest that magnetite becomes magnetic when struck by lightning. Others believe that pieces of magnetite became magnets during Earth's formation, with the domains aligning with Earth's magnetic field while the iron oxide was still molten and malleable.

The most common method for creating magnets today involves placing metal within a magnetic field. The field applies torque to the material, guiding the domains into alignment. A slight delay, known as hysteresis, occurs between the field's application and the domains' realignment; it takes a few moments for the domains to start adjusting. Here’s what happens:

The strength of the resulting magnet depends on the amount of force applied to move the domains. Its permanence, or retentivity, is determined by how difficult it was to align the domains. Materials that are harder to magnetize tend to retain their magnetism for longer periods, whereas materials that are easier to magnetize often revert to their original nonmagnetic state.

A magnet's strength can be diminished or completely nullified by exposing it to a magnetic field aligned in the opposite direction. Additionally, heating the material above its Curie point — the temperature at which an object’s magnetic properties change — can also demagnetize it. The heat distorts the material and agitates the magnetic particles, causing the domains to lose alignment.

Why Magnets Stick

If you've read How Electromagnets Work, you're aware that an electric current flowing through a wire generates a magnetic field. The movement of electrical charges also produces the magnetic field in permanent magnets. However, a magnet's field doesn't arise from a large current moving through a wire — it originates from the motion of electrons.

Many people picture electrons as tiny particles revolving around an atom's nucleus in the same way planets orbit a sun. As current quantum theory explains, the electron's movement is far more intricate than that. In essence, electrons occupy an atom's shell-like orbitals, where they exhibit properties of both particles and waves. Electrons have both charge and mass, and their movement is referred to as spin, which can be either upward or downward.

Typically, electrons fill the atom's orbitals in pairs. When one electron spins upward, its paired counterpart spins downward. It is impossible for both electrons in a pair to spin in the same direction, which is a manifestation of the quantum-mechanical principle known as the Pauli Exclusion Principle.

Although electrons in an atom don't travel very far, their motion is sufficient to create a small magnetic field. Since paired electrons spin in opposite directions, their magnetic fields cancel each other out. However, atoms of ferromagnetic elements contain several unpaired electrons that spin in the same direction. For example, iron contains four unpaired electrons with identical spins. These electrons don't have opposing fields to neutralize their magnetic effects, resulting in an orbital magnetic moment. The magnetic moment is a vector, meaning it has both magnitude and direction. It is linked to the strength of the magnetic field and the torque exerted by the field. A magnet's overall magnetic moment is the sum of the moments from all of its atoms.

In metals like iron, the orbital magnetic moment influences nearby atoms, causing them to align along the same north-south magnetic field lines. Iron and other ferromagnetic materials are crystalline. As they cool from a molten state, groups of atoms with parallel orbital spins align within the crystal structure. This alignment gives rise to the magnetic domains discussed earlier.

It’s no coincidence that the materials which make the best magnets are also the same ones that magnets attract. This is because magnets are drawn to materials with unpaired electrons that spin in the same direction. Essentially, the very property that gives a metal its magnetic qualities also makes it attractive to magnets. Many other elements are diamagnetic — their unpaired atoms produce a field that weakly repels a magnet. A few materials, however, have no magnetic reaction whatsoever.

The explanation behind this phenomenon, rooted in quantum physics, is quite intricate. Without understanding these principles, the concept of magnetic attraction can seem puzzling. It's no wonder, then, that people have been wary of magnetic materials throughout much of history.

Magnet Myths

Whenever you operate a computer, you are engaging with magnets. If your home is equipped with a doorbell, it likely uses an electromagnet to activate the sound. Magnets are also crucial in various devices such as CRT televisions, speakers, microphones, generators, transformers, electric motors, burglar alarms, cassette tapes, compasses, and car speedometers.

Beyond their practical applications, magnets possess fascinating properties. They can generate electric current when placed in a wire and provide torque to power electric motors. Maglev trains use magnetic force to glide at incredible speeds, while magnetic fluids aid in fueling rocket engines.

The magnetic field of the Earth, referred to as the magnetosphere, shields the planet from harmful solar winds. According to Wired magazine, some individuals have even implanted tiny neodymium magnets into their fingers, enabling them to detect electromagnetic fields.

Magnetic resonance imaging (MRI) machines harness magnetic fields to enable doctors to observe the internal organs of patients. Additionally, pulsed electromagnetic fields are used to help treat fractured bones that have not healed properly. This technique, authorized by the United States Food and Drug Administration in the 1980s, can assist in healing bones that resist other treatments. Such electromagnetic pulses may also help mitigate bone and muscle loss in astronauts exposed to extended periods of microgravity.

Magnets can play a role in safeguarding animal health. Cows, for example, are prone to a condition known as traumatic reticulopericarditis or hardware disease, caused by ingesting metal objects. These swallowed items can puncture the cow’s stomach and harm its diaphragm or heart. Magnets are key in preventing such injuries.

One common approach involves using a magnet to pass over the cows' food, removing any metal debris. Another method is feeding the cows magnets directly. Long, slender alnico magnets, referred to as cow magnets, attract metal fragments and help prevent them from damaging the cow’s stomach.

Humans, however, should avoid ingesting magnets, as they can fuse together through the intestinal walls, obstructing blood flow and causing tissue death. In such cases, surgery is often required to remove the magnets.

Some individuals support the use of magnetic therapy for various ailments. Proponents believe that magnetic insoles, bracelets, necklaces, mattresses, and pillows can treat or alleviate conditions ranging from arthritis to cancer. Some also claim that consuming magnetized water can prevent or heal a variety of health issues.

Advocates offer several theories to explain how magnetic therapy works. One suggests that the magnet draws iron from the hemoglobin in the blood, improving circulation to targeted areas. Another theory proposes that the magnetic field alters the structure of surrounding cells.

Despite claims, scientific studies have not provided evidence that static magnets influence pain or illness. Clinical research indicates that any perceived benefits from magnets could be attributed to the passage of time, extra cushioning provided by magnetic insoles, or the placebo effect. Additionally, since drinking water lacks magnetizable elements, the idea of magnetic drinking water remains questionable.