Matter is composed of atoms. Atoms are composed of nuclei and electrons. The nucleus is composed of protons and neutrons, while electrons rotate around the nucleus. Electrons have both charge and spin. When charges move, an electric current is generated; When current exists, a magnetic field is generated. Each electron can be seen as a tiny current loop that generates a tiny magnetic field. This tiny magnetic field is called an atomic magnetic field.

In most substances, the spin direction of electrons in atoms is randomly distributed, so the atomic magnetic field they generate is also disorderly. These atomic magnetic fields cancel out or interfere with each other, resulting in the absence of a clear overall magnetic field for the entire substance. Such substances are called non-magnetic substances. But in some substances, the spin direction of electrons in atoms is arranged in a regular manner, so the atomic magnetic field they generate is also arranged in an orderly manner. These atomic magnetic fields enhance or coordinate with each other, resulting in a clear overall magnetic field for the entire substance. Such substances are called magnetic substances.