Magnets attract or repel objects without direct contact. This ability allows them to stick to refrigerators, guide compasses, and operate various technologies. Understanding how a magnet works involves looking deep inside its structure, down to the atomic level. Magnetism is a fundamental property of matter arising from the behavior of tiny particles within certain materials.
The Atomic Foundation of Magnetism
Magnetism begins with individual electrons. Each electron has an intrinsic property called “spin,” which creates a miniature magnetic field, effectively turning it into a microscopic magnet with a north and south pole. The direction of this spin dictates the orientation of its magnetic field.
In most atoms, electrons exist in pairs. When paired, their opposite spins cause their magnetic fields to cancel, resulting in no net magnetic effect for the atom. However, some atoms have “unpaired” electrons. These unpaired electrons contribute a net magnetic moment, making the entire atom act like a tiny magnet.
Magnetic Domains
In materials with atoms having a net magnetic moment, these atomic magnets align within microscopic regions called magnetic domains. Within each domain, billions of atomic magnetic moments align in the same direction, creating a strong localized magnetic field.
In an unmagnetized material, these magnetic domains are oriented randomly. Their magnetic fields point in different directions, canceling each other out across the material. This random arrangement means the material does not exhibit an overall external magnetic field. However, the potential for magnetism exists by aligning these domains.
Making a Magnet
To magnetize a material, an external magnetic field is applied. This field forces the randomly oriented magnetic domains to rotate and align with its direction. As domains align, their collective magnetic fields reinforce, creating an overall magnetic field for the material. For permanent magnets, this alignment persists even after the external field is removed.
Permanent magnets are often manufactured by heating materials, like certain alloys, to a high temperature and cooling them in a strong magnetic field. This solidifies domain alignment, allowing the material to retain magnetism indefinitely. Temporary magnets, such as a paper clip, lose magnetism once the external field is removed as their domains quickly revert to a random orientation.
Different Kinds of Magnetic Materials
Materials respond to magnetic fields differently based on their atomic structure and electron configurations. Ferromagnetic materials, like iron, nickel, and cobalt, are strongly attracted to magnets and can be permanently magnetized. They possess unpaired electrons and a crystal structure allowing their atomic magnetic moments to easily align into stable magnetic domains. When an external magnetic field is applied, their domains readily align, producing a strong magnetic effect.
Paramagnetic materials are weakly attracted to magnetic fields but do not retain magnetism once the external field is removed. They have unpaired electrons, but their atomic magnetic moments are randomly oriented due to thermal motion and do not form stable domains. Diamagnetic materials are weakly repelled by magnetic fields. In these materials, all electrons are paired, and their magnetic properties arise from a slight realignment of electron paths that opposes the external field.