Why can some substances be adsorbed by magnets? Here we use the most common example - iron to illustrate. Iron is a metallic element that belongs to ferromagnetic materials, characterized by strong reactions to external magnetic fields. When there is no external magnetic field, the arrangement of atoms in iron is relatively chaotic, with many small magnetic dipoles generated by electron spins and orbital movements in different directions around each atom. These small magnetic dipoles cancel out each other or are randomly distributed, resulting in an overall lack of significant net magnetism.

When there is an external magnetic field, the situation is different. An external magnetic field will apply a force or torque to the small magnetic dipoles inside the iron, causing them to tend to align with the direction of the external magnetic field. In this way, small magnetic dipoles that were originally disorganized or had different directions will be arranged into an ordered structure, which we call magnetic domains. Each magnetic domain is equivalent to a miniature permanent magnet, with its own North and South poles. When most or all of the small magnetic dipoles are aligned with the direction of the applied magnetic field, the entire piece of iron will exhibit significant net magnetism and align with the direction of the applied magnetic field. This process is called magnetization.