What is magnetism? What can be divided into metal materials by magnetism?
Ferromagnetism, such as Fe, Co, Ni and other substances, at room temperature, magnetic susceptibility of up to 10^-3 orders of magnitude, said the magnetic properties of this kind of material is ferromagnetic. Ferromagnetic material, even in a weak magnetic field, can also obtain very high magnetization, and when the external magnetic field is removed, it can still retain very strong magnetism. The magnetic susceptibility is positive, but when the external field increases, the H becomes smaller due to the rapid saturation of magnetization. Ferromagnetism has a strong magnetic property, mainly due to their strong internal exchange fields. The exchange energy of ferromagnetic material is positive and larger, so that the magnetic moment of adjacent atoms is parallel oriented (corresponding to the steady state), and many small domains - magnetic domains are formed in the material. Each domain has about 1015 atoms. The magnetic moments of these atoms are arranged in the same direction, assuming that there is a strong internal field called the molecular field inside the crystal, and that the molecular field is enough to automatically magnetize each domain. This self - generated magnetization is called spontaneous magnetization. Because of its existence, ferromagnetic material can be magnetized strongly in a weak magnetic field. Therefore, spontaneous magnetization is the basic characteristic of ferromagnetic materials, and is also the difference between ferromagnetic materials and paramagnetic materials. The ferromagnetic magnet only below a certain temperature do not appear, beyond the temperature due to internal heat disturbance damage material oriented parallel electron spin magnetic moment, the spontaneous magnetization is 0, the ferromagnetism disappeared. This temperature is called the Curie point.
The main characteristic of paramagnetic paramagnetic material is that the permanent magnetic moment exists in the atom no matter whether the external magnetic field exists. But in the absence of external magnetic field, the paramagnetic substance of atomic thermal vibration, irregular macro view, no magnetism; under the external magnetic field, each atomic magnetic moment comparison rules orientation, showed very weak magnetic material. The magnetization is the same as the direction of the external magnetic field, and is strictly proportional to the external magnetic field H. The magnetic properties of paramagnetic materials depend on temperature as well as H. Its magnetic susceptibility H is inversely proportional to the absolute temperature T. In the formula, the C is called the Curie constant, depending on the magnetization and magnetic moment of the paramagnetic material. Generally, the magnetic susceptibility of paramagnetic materials is very small, and the H is about 10^-5 at room temperature. Atoms or molecules that contain odd numbers of electrons, atoms or ions that are not filled with electrons, such as transition elements, rare earth elements, steel elements, and aluminum and platinum, are paramagnetic materials.
When the magnetization is M negative, the solid is diamagnetic. Bi, Cu, Ag, Au and other metals have this property. In an external magnetic field, the magnetic induction inside the magnetized medium is less than the magnetic induction intensity in the vacuum M. The magnetic moment of an atom (ion) of a diamagnetic substance should be zero, i.e., there is no permanent magnetic moment. When the diamagnetic material is placed in an external magnetic field, the external magnetic field changes the electron orbit and induces a magnetic moment opposite to the external magnetic field, which exhibits diamagnetic properties. So diamagnetic comes from changes in the orbital state of electrons in atoms. Generally, the diamagnetic properties of diamagnetic materials are very weak. The magnetic susceptibility H is generally about -10-5, and is negative.
