Speaking of magnetic matirals, we have to say “magnetism”. Experiments show that any material in the external magnetic field can be more or less magnetized, just the degree of magnetization. According to the characteristics of materials in external magnetic field, materials can be divided into five categories : paramagnetic materials, diamagnetic materials, ferromagnetic materials, ferroporphyrin-magnetic materials, antiferro-magnetic materials.
Paramagnetic materials: a substance that, when moved close to a magnetic field, is magnetized in the direction of a field, but it’s so weak that it requires a precise instrument to measure it. If you remove the external magnetic field, the internal magnetic field will return to zero, making it non-magnetic. Such as aluminium, oxygen, etc.
        Diamagnetic materials: it’s something with a negative susceptibility. When acted upon by an external magnetic field, an induced electronic circulation in the molecule produces a magnetic moment in the opposite direction to the external magnetic field, in other words, the magnetic field after magnetization and the direction of the external magnetic field opposite. All organic compounds have diamagnetic properties, such as graphite, lead and water.
        Ferromagnetic materials: it’s a kind of material magnetized under the action of external magnetic field, even if the external magnetic field disappears, it can still keep its magnetized state with magnetism. Such as iron, cobalt, nickel are all ferromagnetic materials.
        Ferroporphyrin-magnetic materials: macromagnetism is the same as ferromagnetism, except that the magnetic susceptibility is low. Typical ferroporphyrin-magnetic material is ferrite. The most striking difference between them and ferromagnetic materials is their internal magnetic structure.
        Antiferro-magnetic materials: In an antiferro-magnetic material, the spin of the adjacent valence electrons tends in the opposite direction. The material has a net magnetic moment of zero and produces no magnetic field. This material is less common, and most antiferro-magnetic materials only exist at low temperature. If the temperature exceeds a certain value, it usually becomes paramagnetic. Such as chromium, manganese.
We refer to paramagnetic and diamagnetic materials as weak magnetic materials, and ferromagnetic materials and ferroporphyrin-magnetic materials as strong magnetic materials. Generally speaking, magnetic materials refer to strong magnetic materials. Magnetic materials according to its usage can be divided into:
       Soft magnetic materials: magnetic materials with low coercivity and high permeability can achieve maximum magnetization with the minimum external magnetic field. Soft magnetic materials are easy to magnetize and easy to demagnetize. For example, soft magnetic ferrite, amorphous nanocrystalline alloys.
       Hard magnetic materials: also known as permanent magnetic materials, refers to difficult magnetization and once magnetized after the difficult demagnetization of materials , its main characteristics are high coercivity, including rare earth permanent magnetic materials, metal permanent magnetic materials and permanent magnetic ferrite.
       Functional magnetic materials: It mainly has magnetostriction material, magnetic recording materials, magnetoresistive materials, magnetic bubble material, magneto-optic material and magnetic thin film materials etc.
The family of magnetic materials includes a large number of members, some common and commonly used materials on the market are listed in the figure above. With the progress and development of the science and technology, new magnetic materials have been discovered and applied. Similarly, some materials with low performance and high cost have been eliminated.