(The magnetic component ms of the spin Quantum number s is+1/2 and -1/2, marked with ↑ and ↓ respectively) pairing without producing net spin S and the corresponding magnetic moment, so it often does not show magnetism. On the contrary, when the substance is composed of molecules containing unpaired electrons, the existence of the net spin in the molecule causes the magnetism of the substance. The magnetic moment caused by the spin of each atom or the total spin of the molecule S can be μ It is regarded as a small magnet (often called magneton). Generally, for this molecular magneto subsystem, the macroscopic magnetic moment produced by a substance containing one mole of molecules is defined as the magnetization M. When there is no external magnetic field H and high temperature T, the magneton does not show macroscopic magnetism due to its disordered orientation, but the magnetization M will increase with the decrease of temperature T and the increase of magnetic field strength H. The average magnetic moment can be approximately derived from Statistical mechanics μ- The Curie approximation formula for: μ-=μ 2H3kT, (1) where k is the Boltzmann constant. According to the macroscopic experimental results of samples showing different M value changes under the external magnetic field H (usually the direction of the external magnetic field is defined as the z direction), magnetic substances can be divided into several types: Diamagnetism (also known as diamagnetism, no net spin, and weak induced magnetic field opposite to the external field induced by Lenz's law), Paramagnetism (spin disorder), ferromagnetism (spin parallel, ↑↑), Antiferromagnetism (antiparallel spin, ↑↓), Ferrimagnetism (antiparallel spin, but the two spins in opposite directions are not equal, ↑↓), inclined ferromagnetism (antiparallel spin, but structural factors force the two spins not to reach completely opposite directions, so that the remaining net spin is left, ↗↘) And metamagnetic (Antiferromagnetism to ferromagnetic transition) magnets.