Permanent magnets — whether powerful Neodymium magnets or common Ferrite magnets — have a remarkable ability: they stay magnetized for years and can exert force through air, glass, wood, and even non-ferrous metals. But what makes this possible?
The answer lies in their internal structure.
Inside magnetic materials are tiny regions called magnetic domains. In ordinary materials, these domains point in random directions, cancelling each other out. In a permanent magnet, however, most of these domains are aligned in the same direction. This alignment is stable and resistant to disturbance, which is why the magnet remains magnetized for a long time.
Every permanent magnet has two poles: North (N) and South (S). Between these poles, magnetic flux lines constantly exist. These invisible lines form the magnetic field that surrounds the magnet and extends into the space around it.
When a piece of steel (or any ferrous material) is placed within this magnetic field, it becomes temporarily magnetized. The magnet induces an opposite polarity in the steel, which creates attraction. In simple terms, opposite poles attract — and that is why the steel is pulled toward the magnet.
The strength of this attraction depends on the magnetic flux density in the material. Importantly, the pulling force increases with the square of the flux density. This means that even a small increase in magnetic strength can produce a much larger increase in holding force.
Magnetic fields can also be controlled. A “keeper” steel plate placed across the poles of a magnet provides a low-resistance path for the magnetic flux. This effectively contains most of the flux within the steel, reducing the external magnetic field. As a result, nearby steel objects will not be strongly attracted.
This principle is commonly used during transport. Magnets are often stored with keeper plates or inside steel boxes to prevent magnetic flux from extending outward and interfering with sensitive electronics, such as aircraft instruments.
Permanent magnets may seem mysterious, but their behavior is governed by well-understood physical principles of domain alignment and magnetic flux control.