Diamagnetism is that the electronic magnetic moments in the atoms of some substances cancel each other, and the combined magnetic moment is zero. However, when subjected to an external magnetic field, the orbital motion of the electron will change, and a small magnetic moment will be generated in the opposite direction to the external magnetic field. In this way, the magnetic susceptibility that indicates the magnetic properties of the substance becomes a very small negative number (amount). Magnetic susceptibility is the ratio of the combined magnetic moment (called magnetization) of a substance under the action of an external magnetic field and the magnetic field strength, and the symbol is κ. Generally, the magnetic susceptibility of a diamagnetic substance is about one part per million (-10-6).