The magnetic domain theory uses quantum theory to explain the magnetization mechanism of ferromagnetic materials microscopically. The so-called magnetic domain refers to the magnetic material inside a small area, each area contains a large number of atoms, the magnetic moments of these atoms are arranged as a small magnet orderly, but the adjacent magnetic moments between different regions of the arrangement The directions are different.
The interface between each magnetic domain is called a domain wall. Macroscopic objects generally always have many magnetic domains. In this way, the magnetic moment directions of the magnetic domains are different, the results cancel each other out, the vector sum is zero, the magnetic moment of the whole object is zero, and it cannot attract other magnetic materials. That is, the magnetic material does not show magnetism externally under normal conditions. Only when magnetic
After the material is magnetized, it can show magnetism externally. In the middle school physics textbooks, the current teaching reform version of the Ordinary High School Curriculum Standards Experiment Textbook. Physics used in the curriculum reform pilot area (Shandong, Jiangsu, Hainan, Ningxia, and Guangdong) uses the magnetic domain theory and is now used in most areas. The teaching of the textbook “Full-time General High School Textbooks and Physics.” explains the principle of magnetization in the use of Ampere's molecular current hypothesis.