You notice magnetism when electrons in a material move and spin in certain ways, which causes the material to display magnetic properties. If electrons are not paired, they create small magnetic moments that can join together, and this often causes the material to become magnetic. The atomic structure determines if these moments line up, which causes the material as a whole to be magnetic.
Unpaired electrons often cause the material to have strong magnetic effects.
Paired electrons usually cause the material to have weak or no magnetism.
The way atoms are arranged also causes the material to interact differently with magnetic fields.
Table of Contents
Key Takeaways
Magnetism happens because electrons move and spin in materials. Unpaired electrons make magnetism stronger.
How atoms are arranged decides if a material is magnetic. Materials with unpaired electrons, like iron, can be very magnetic.
Magnetic moments come from how electrons spin and move. More unpaired electrons make the magnetic moment stronger.
Ferromagnetic materials, like iron and cobalt, keep magnetism after the outside magnetic field goes away. This makes them good for permanent magnets.
Learning about magnetism helps us use it in many things. We use it in electric motors and MRI machines. Magnetism makes technology and life better.
Causes the Material to Be Magnetic
Electron Spin
Electron spin is like a tiny spinning top inside each electron. This spin gives the electron a small magnetic moment, like a little bar magnet. Electron spin is very important for magnetism. Here are some key ideas:
Electron spin is a basic part of electrons and gives them a magnetic moment.
The spin helps decide how atoms form and act in a magnetic field.
In materials with unpaired electrons, like iron, the spins can line up and make a strong magnetic force.
The Pauli exclusion principle says two electrons in an atom cannot have the same quantum numbers. If electrons share an orbital, they must have different spins. This rule explains why some electrons stay unpaired, which helps cause magnetism. Unpaired electrons have spins that do not cancel out, so their magnetic moments add together.
Note: How electrons spin and line up decides if a material will be strongly magnetic. If the spins match up, you get a strong magnetic field. If they do not, the magnetic effects cancel each other.
Magnetic Moments
Electrons moving inside atoms create magnetic moments. You can think of each electron as a tiny magnet because of its charge and movement. Both the spinning and moving of electrons add to the atom’s magnetic moment. Magnetism often depends on how many unpaired electrons are in the atom.
Magnetic moments come from both electron spin and movement.
More unpaired electrons mean a stronger magnetic moment.
The total magnetic moment is the sum of all the tiny magnets from unpaired electrons and their movement.
For example, a cobalt ion with three unpaired electrons has a much stronger magnetic moment than an atom with all paired electrons. The formula (mu_{eff} approx sqrt{n(n+2)}) shows that more unpaired electrons make the magnetic moment bigger. This is why iron, cobalt, and nickel can be magnetized, but others cannot.
Experiments show that when electrons line up in a certain way, the material can react to a magnetic field. In some materials, spinning electrons can switch direction, which is important for new technology like spintronics.
Common Misconception: Many people think all metals are magnetic, but only some materials with the right atomic structure and unpaired electrons, like iron, are strongly attracted to magnets. Most metals, such as aluminum and copper, do not have this property.
When you put a magnet near a material, the way magnetic moments line up inside decides if it will be attracted. The poles of a magnet are where the force is strongest, and this force comes from how electrons move and spin inside atoms.
Atomic Structure and Magnetism
Magnetic Dipoles
A magnetic dipole is like a tiny magnet in each atom. These dipoles form when electrons move around the nucleus. The movement of electrons makes a magnetic moment. This is similar to how electricity in a wire makes a magnetic field. In a hydrogen atom, the electron moves in a circle. This movement creates a magnetic field. Even one atom can act like a small magnet. The strength of the magnetic moment depends on how the electron moves. The direction of the magnetic moment is opposite to how the electron spins. This happens because electrons have a negative charge.
How electrons are arranged in an atom decides if it has a magnetic moment.
Atoms with unpaired electrons show magnetism, but atoms with paired electrons do not.
The orbital magnetic dipole moment comes from electrons moving around the nucleus.
When you look at materials with many atoms, dipoles can interact. These interactions can cause interesting effects. In nanoparticles, dipoles can work together and create new magnetic states. This changes how the material reacts to a magnetic field. Dipoles can also affect the magnetic force through exchange interactions. This can cause things like exchange bias.
Magnetic Domains
Ferromagnetic materials have areas called magnetic domains. In each domain, atoms’ magnetic moments point the same way. Domains form when the material cools below the Curie temperature. Domains help the material use less energy. Domain walls separate these areas. The direction of magnetization changes slowly across these walls.
Magnetic domains often start at defects, impurities, or surfaces.
Domains get bigger as domain walls move to lower energy.
The size and shape of domains depend on what the material is made of.
When you use an outside magnetic field, domains start to line up with it. As the field gets stronger, more domains line up. This makes the material more magnetic. If you keep making the field stronger, all domains can line up. The material then reaches its highest magnetization. If treated right, this can make the material a permanent magnet.
Faraday’s Law of Induction tells us that a changing magnetic field can make an electric field. The equation for the induced electromotive force (EMF) is
[mathrm { EMF } = - mathrm { N } dfrac { Delta Phi } { Delta mathrm { t } }]
This law helps explain how magnetism can be made in a material. The EMF is strongest when the magnetic flux changes quickly. The direction of the current always goes against the change, as Lenz’s Law says.
How electrons, dipoles, and domains are arranged decides how strong the magnetic force is. When domains line up, their magnetic moments add together. This makes the material’s magnetic field stronger. The poles of a magnet are where this force is easiest to see.
Types of Magnetic Materials
There are three main types of magnetic materials. These are ferromagnetic, paramagnetic, and diamagnetic. Each type acts differently when near a magnet. The difference comes from how electrons are inside the atoms. The table below shows how each type acts:
Material Type | Magnetic Behavior | Magnetism Retention |
|---|---|---|
Ferromagnetic | Strong pull to both ends of a magnet. | Can keep magnetism even after the magnet is gone. |
Paramagnetic | Weak pull to one end of a magnet. | Loses magnetism when the magnet is taken away. |
Diamagnetic | Pushes away from both ends of a magnet. | Also loses magnetism when the magnet is taken away. |
Ferromagnetic
Ferromagnetic materials make the strongest magnets. Iron, cobalt, and nickel are good examples. These materials have unpaired electrons in their d-orbitals. The unpaired electrons point the same way. This makes a strong magnetic force. When you put a ferromagnetic material in a magnetic field, the atoms’ magnetic moments line up. This stays even after you take away the field. That is why you can make permanent magnets from iron or steel. The crystal structure helps keep the moments lined up. You often see steel used in magnets because it keeps its strength.
Ferromagnetic materials are strongly pulled to magnets.
You can use them to make permanent magnets.
Iron and steel are common in tools and machines.
Paramagnetic
Paramagnetic materials have some unpaired electrons. But the magnetic moments do not stay lined up. When you put them in a magnetic field, the unpaired electrons try to line up. This makes a weak pull. When you take away the field, the magnetism goes away. Aluminum and platinum act this way. These materials do not become permanent magnets. Their magnetic strength is much weaker than ferromagnetic materials.
Paramagnetic materials have unpaired electrons.
The pull to a magnet is weak and does not last.
You will not find strong magnets made from these.
Diamagnetic
Diamagnetic materials have all electrons paired. This means the magnetic moments cancel out. When you put them in a magnetic field, they make a weak force in the opposite direction. This pushes the material away from both ends of a magnet. Copper, bismuth, and water act this way. Diamagnetic materials never become magnets. Their magnetic strength is always very weak.
Diamagnetic materials have no unpaired electrons.
They are weakly pushed away from a magnetic field.
You cannot use them to make magnets.
Tip: To check if a material is magnetic, look at the electrons. Unpaired electrons mean it could be magnetic. All paired electrons mean it will not be strongly magnetic.
Only some materials, like iron and steel, are naturally magnetic. These have the right electron arrangement and crystal structure. The strongest magnets are ferromagnetic. Their magnetic moments add up and stay lined up. When you put opposite poles together, you feel the strongest pull. How electrons move and line up decides the material’s magnetic strength and how it acts near a magnet.
Measuring Magnetism
Magnetic Field Strength
You can find out how magnetic something is by checking a few things. The main way is to measure the magnetic field strength. This tells you how strong the magnetic field is near a magnet or inside a material. Scientists use units like amperes per meter (A/m) and oersted (Oe) for this. When talking about magnetic flux density, they use tesla (T) and gauss (G). Magnetic flux density shows how much magnetic force goes through an area.
Here is a table that lists ways to measure magnetic strength:
Method | Description | Units |
|---|---|---|
Magnetic Field Strength (H) | Tells how strong the magnetic field is from a magnet. | A/m or Oe |
Magnetic Flux Density (B) | Shows how much magnetic force passes through an area. | T or G |
Coercivity (Hc) | Tells how well a magnet can keep from losing its magnetism. | Oe or A/m |
Magnetic Moment (m) | Shows how strong and which way the magnet’s field points. | A·m² or J/T |
Pull Force | Tells the most force you can use before a magnet comes off. | lb or N |
Saturation Magnetization (Ms) | Shows the highest magnetism a material can reach. | A/m |
You can see these measurements with Earth’s magnetic field. The core of Earth has a field strength of about 25 gauss. The surface is much weaker, only about 0.5 gauss. Scientists use special tools to find these numbers.
Tip: To see how magnetic something is, check its magnetic field strength and pull force.
Applications
You use magnetism all the time, even if you do not see it. Magnetic materials are important in many jobs and machines. For example, an electromagnet can pick up scrap metal in junkyards. Electric motors use magnets to spin and make things move. Magnetic sensors help cars stop safely with ABS. In mining and food factories, magnets pull out metal pieces.
Here are some ways magnetism is used:
Transformers move electricity from one place to another.
Inductive charging lets you charge things without wires.
Maglev trains float above tracks using strong magnets.
MRI machines use strong magnets to make pictures of your body. These machines work by seeing how electrons act in magnetic fields, so doctors can look inside you.
Application | Description |
|---|---|
Mining | Strong magnets pull out metals and ore. |
Electromagnetic vacuum cleaner | Picks up metal objects in work areas. |
Electric motor | Uses magnets to make things move. |
Magnetic sensors | Find changes in magnetic fields in cars and machines. |
Transformers | Move electricity using magnetic fields. |
Inductive charging | Charges devices without wires. |
Maglev trains | Use magnets to float and move fast. |
Note: Magnetism helps you in medicine, travel, and electronics. You see it when magnets stick to your fridge, and you use it in MRI scans.
You notice magnetism when electrons move and spin. This makes magnetic fields in the material.
If electrons are not paired, they cause strong magnetic effects.
How atoms are arranged decides if something acts like a magnet.
Discovery | How It Helps Us |
|---|---|
MRI Machines | Doctors can look inside your body |
Many things you use need these to work | |
New magnetism makes computers faster |
Learning about magnetism helps you use cool technology. It also helps you understand how things work. The main reason is how electrons act and how atoms are built.
FAQ
Why are some metals magnetic and others not?
Iron is magnetic because it has unpaired electrons. Copper has paired electrons, so its magnetic moments cancel out. Only metals with the right atomic structure are strongly magnetic.
Can you make a non-magnetic material magnetic?
Sometimes you can make a non-magnetic material magnetic. You can do this by changing its temperature or mixing it with other elements. But if a material only has paired electrons, it will not become magnetic.
What happens if you cut a magnet in half?
If you cut a magnet in half, you get two smaller magnets. Each piece will have a north and south pole. The magnetic domains inside line up again, so both pieces act like full magnets.
How do magnets lose their magnetism?
A magnet can lose its magnetism if you heat it, drop it, or hit it. These things mess up the way the magnetic domains are lined up. The magnet then gets weaker or stops working.