Many people have played with magnets since childhood, knowing they can attract iron nails and repel other magnets. Yet few truly understand the underlying principles and classifications of magnets. Essentially, a magnet is a material with orderly aligned internal magnetic domains that can generate an external magnetic field. It only adheres to ferromagnetic substances such as iron, cobalt and nickel, and exerts no attractive force on copper, aluminum, plastic, glass and other materials.
Every magnet has two poles: the north (N) pole and the south (S) pole, and always follows the physical rule that like poles repel while opposite poles attract. No matter how many pieces you cut a magnet into, each fragment will automatically form a complete pair of magnetic poles; isolated magnetic monopoles do not exist. If a magnet is subjected to prolonged high temperatures, heavy impact or strong electric current shocks, its internal magnetic domains will become disordered. The magnet will gradually demagnetize, and its pulling force will drop significantly.
Commercially available magnets fall into two major categories: permanent magnets and electromagnets. Permanent magnets retain magnetism long-term without power supply. Common varieties include cost-effective ferrite magnets, high-strength NdFeB strong magnets, and AlNiCo magnets, widely adopted for civilian products and small equipment. Electromagnets rely on energized coils to produce magnetic fields; their magnetism vanishes once power is cut off, and pull strength can be adjusted by changing current, making them suitable for large-scale industrial control.
Magnets have been used since ancient times. Ancient people created compasses from natural lodestones to solve navigation problems for overland and maritime travel. In modern daily life, magnetic fridge seals, loudspeakers, mobile accessories and magnetic door catches are ubiquitous. Industry depends on magnets for motors, generators, magnetic jigs and lifting magnets. High-end sectors including new energy vehicles, wind power generation, medical MRI and precision instruments rely heavily on high-performance NdFeB permanent magnets. Tiny magnetic materials have become indispensable basic industrial raw materials powering modern society.