Diamagnetism

Some things do not like magnets.

A magnet can push them away. This push is called diamagnetism.

Most things have this push. It is very weak. You cannot see it every day. But some things push back more.

Water and wood are examples. Even gold and copper do this.

Bismuth is a very strong pusher.

Special tools can see the push. Some materials can even float. A scientist once made a frog float!

It is amazing to see things fly.

Most things in our world respond to magnets. Some things are pulled toward a magnet. Others are pushed away. This pushing force is called diamagnetism.

Diamagnetism happens in all materials. It occurs because a magnetic field makes a tiny, new magnetic field inside the object. This new field points in the opposite direction. This causes the object to be pushed away. In most things, this push is very weak. You might not even notice it. But some materials are different. These are called diamagnetic materials.

Water, wood, and most plastics are diamagnetic. Many metals like gold, silver, and copper are too. Bismuth is a very strong diamagnet.

Sometimes, the push is strong enough to make things float. This is called levitation. A thin piece of pyrolytic carbon can float above magnets. Scientists have even used very strong magnets to float a live frog!

Superconductors are special. They are perfect diamagnets. They push out all magnetic fields from their inside. This is known as the Meissner effect.

Magnetism is a force we see every day. Most people know that magnets can pull on certain metals like iron. However, some materials respond to magnets in a different way. They do not pull toward the magnet. Instead, they are pushed away by it. This pushing force is a property called diamagnetism.

It is a fascinating part of how the physical world works. Even though we do not feel it often, it is happening all around us.

How does this pushing work? It all happens because of how electrons move inside an object. When you bring a magnetic field near a material, it creates a new magnetic field inside that material. This new field points in the opposite direction of the one you applied. Because the two fields point in opposite ways, they push against each other. This creates a repulsive force that moves the object away.

In most things, this effect is very weak and hard to see. But in special materials, the push is much stronger.

Scientists have been studying this for a long time. In 1778, a man named Anton Brugmans noticed something interesting. He saw that a metal called bismuth was repelled by magnetic fields. Later, in 1845, the famous scientist Michael Faraday showed that this was a property of all matter. He proved that every material responds to a magnetic field in some way. Faraday even used the name "diamagnetic" for this effect. He chose this name because the prefix "dia-" means to go through or across.

There are many different materials that show this behavior. Some common things like water, wood, and plastic are diamagnetic. Many metals are also diamagnetic, including copper, gold, silver, and mercury. Bismuth is one of the strongest common diamagnets. There are also special materials called superconductors. These are "perfect" diamagnets because they push all magnetic fields out of their inside. This special action is called the Meissner effect.

Even tiny particles like atoms can be diamagnetic if all their electrons are paired up.

Sometimes, the push from diamagnetism is strong enough to make things float. This is called levitation. You can see a thin slice of pyrolytic carbon float above magnets at room temperature. Scientists have even used very powerful magnets to levitate a live frog.

In 2009, NASA's Jet Propulsion Laboratory used strong magnets to levitate mice. This helps scientists study how life changes without the pull of Earth's gravity. It shows how a tiny force can lead to big discoveries.

Diamagnetism is a fundamental property of matter where a material is repelled by a magnetic field. When an external magnetic field is applied to a substance, it induces an internal magnetic field that points in the opposite direction. This opposing field creates a repulsive force that pushes the material away from the magnetic source. While many people think of magnetism as an attractive force, such as with iron, diamagnetism is a universal phenomenon. In fact, diamagnetism is a quantum mechanical effect that occurs in all materials.

The mechanism behind this repulsion involves the behavior of electrons. Electrons generally reside in orbitals, which can be thought of as tiny loops of electric current. When a magnetic field is introduced, it changes the orbital motion of these electrons. This change induces magnetic dipole moments within the atoms or molecules. These induced moments align themselves in a direction opposite to the external field. Because the induced field opposes the applied field, the material experiences a push.

Scientists categorize materials based on how they respond to these magnetic forces. In most substances, diamagnetism is a very weak effect. This is because other forms of magnetism, like paramagnetism or ferromagnetism, are much stronger. Paramagnetic and ferromagnetic materials are attracted to magnetic fields because their internal magnetic dipoles align with the external field. In these cases, the strong attractive force overcomes the weak diamagnetic repulsion. A substance is only called a "diamagnet" when the diamagnetic response is the strongest effect present.

In chemistry, a simple rule helps identify whether a particle is diamagnetic or paramagnetic. If all the electrons in an atom, ion, or molecule are paired, the substance is diamagnetic. If the particle has any unpaired electrons, it is paramagnetic. This distinction is crucial for understanding how different elements will react to magnetic environments. Many common substances are diamagnetic, including water, wood, petroleum, and most plastics. Several metals also show this property, such as copper, gold, silver, mercury, and lead.

The history of this discovery began in 1778 when Anton Brugmans observed that bismuth was repelled by magnetic fields. In 1845, Michael Faraday conducted experiments to demonstrate that this was a universal property of matter. Faraday concluded that every material responds to a magnetic field in some way. On a suggestion from William Whewell, Faraday used the term "diamagnetic." The prefix "dia-" means to go through or across. Faraday later adjusted the term to the noun "diamagnetism."

While diamagnetism is usually too weak to notice, some materials show extreme versions of this effect. Superconductors are considered perfect diamagnets. This is due to the Meissner effect, where a superconductor entirely expels any magnetic field from its interior.

Other materials show much higher susceptibility than water. For example, the magnetic susceptibility of water is approximately -0.91 x 10⁻⁵. Bismuth is one of the strongest common diamagnets with a susceptibility of -16.6 x 10⁻⁵. Pyrolytic carbon is even more extreme, reaching a susceptibility of -40.9 x 10⁻⁵ in one plane.

Because diamagnets are attracted to magnetic field minima, they can achieve stable levitation. This allows objects to float without consuming any power. A thin slice of pyrolytic graphite can float above permanent magnets at room temperature. Scientists have used even more powerful magnetic fields to achieve spectacular results. In the Netherlands, researchers successfully levitated water and even a live frog. In 2009, NASA's Jet Propulsion Laboratory levitated mice using a superconducting magnet.

These experiments help researchers study how life behaves in microgravity, which is useful for understanding bone and muscle mass in space.