Cutting a bar magnet in half will not remove its poles. It will produce just two magnets, each with a north pole which will be attracted to the south pole of the other magnet, and vice versa.
It’s this fundamental property of attraction that makes magnets useful for so many purposes, from holding a party invitation to a refrigerator to performing medical imaging.
But how do these poles appear? Why do magnets have north and south poles?
Magnets are “one of the deepest mysteries in physics”, says Greg Boebinger (opens in a new tab), director of the National High Magnetic Field Laboratory in Tallahassee, Florida. While people have been using magnets for thousands of years (opens in a new tab)scientists are still learning new things about how they work.
The most fundamental answer to why magnets have poles lies in the behavior of electrons. All matter, including magnets, is made up of atoms. In each atom, the nucleus is surrounded by one or more negatively charged electrons. Each of these electrons generates its own small magnetic field, which scientists call a “spin”. If enough of these small magnetic fields point in the same direction, the material itself becomes magnetic.
Related: Why does metal spark in the microwave?
The “spin” of an electron is somewhat of an abstract concept, Boebinger told Live Science. Technically, no one has seen an electron spin – it’s far too small to be seen under a microscope. But physicists know that electrons have a magnetic field because they have measured it. And one way this field could be generated is if the electron was spinning. Reverse the direction of the spin and the magnetic field would flip.
When it’s possible, the electrons will pair up so that their spins cancel each other out (opens in a new tab), making the net magnetism of an atom zero. But in some elements, like iron, this cannot happen. The number of electrons and the way they are positioned around the nucleus means that each iron atom will have an unpaired electron generating a small magnetic field.
In an unmagnetized material, these individual magnetic fields point in different random directions. In this state, they mostly cancel each other out, so the material is not globally magnetic. But under the right conditions, the tiny subatomic magnetic fields can align to point in the same direction. You could think of this as the difference between a crowd of people hurrying together and getting organized and facing in the same direction. The combination of these very small magnetic fields creates a larger magnetic field – so the material becomes a magnet.
Many magnets used in everyday life, such as fridge magnets, are called permanent magnets. In these materials, the magnetic fields of many atoms in the material have become permanently aligned by an external force – such as by being placed inside a stronger magnetic field.
Often this stronger magnetic field is created by electricity. Electricity and magnetism are fundamentally linked because magnetic fields are generated by the movement of electric charges. This is why a spinning electron has a magnetic field. But scientists can also harness electricity to create very powerful magnets, said Paolo Ferracin (opens in a new tab), principal investigator at the Lawrence Berkeley National Laboratory in California. Passing enough current through a coil of wire generates a very strong magnetic field that lasts as long as the current is flowing. These electromagnets are often used in physics research, Ferracin told Live Science. They are also used in medical tools such as magnetic resonance imaging (MRI) machines.
The Earth also has its own magnetic field – this is what makes a compass needle work. Scientists defined the north pole of a magnet as the end that would point toward the Earth’s north pole if the magnet could spin freely. But technically, Boebinger explained, that means the magnetic north pole on Earth is actually a magnetic south pole, because opposite poles attract.
In physical convention, magnetic field lines flow from the magnet’s north pole to its south pole, forming a closed loop.
Physicists have also found other arrangements of magnetic poles, including quadrupoles (opens in a new tab), in which a combination of north and south magnetic poles are arranged in a square. But one goal remains elusive, Ferracin said: No one has yet found a magnetic monopoly.
Electrons and protons are electrical monopoles: they each have a single electrical charge, positive or negative. But electrons (and other particles too) have two magnetic poles. And since they are fundamental particles, they cannot be broken down any further. This difference between how particles behave electrically and magnetically has intrigued many physicists, and for some, finding a particle with a single magnetic pole is the holy grail. Its discovery would challenge the laws of physics as we currently understand them.
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