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How magnetic materials record information
Any substance can be more or less magnetized in an external magnetic field, but the degree of magnetization is different. According to the characteristics of substances in external magnetic fields, substances can be roughly divided into three categories: paramagnetic substances, diamagnetic substances, and ferromagnetic substances.
According to the molecular current hypothesis, the material should exhibit generally similar characteristics in the magnetic field, but here we tell that the characteristics of the material in the external magnetic field vary widely. This reflects the limitations of the molecular current hypothesis. In fact, there are differences in the microstructure of various substances. This difference in the structure of matter is the cause of differences in the magnetic properties of materials.
We call paramagnetic and diamagnetic materials ferromagnetic materials called ferromagnetic materials called ferromagnetic materials. The so-called magnetic material refers to a ferromagnetic material. The difficulty of magnetic material demagnetization after magnetization can be divided into soft magnetic material and hard magnetic material. Magnetic materials that are easily removed after magnetization are called soft magnetic materials. Materials that are not easily touched are called hard magnetic materials. In general, the remanence of a soft magnetic material is small. Hard magnetic materials have large remanence.
Magnetic materials are divided according to chemical composition. Commonly there are two major categories: metallic magnetic materials and ferrites. Ferrite is a magnetic oxide mainly composed of iron oxide. The remanence of soft magnetic materials is weak, and it is easy to demagnetize. Suitable for applications requiring repetitive magnetization. It can be used to manufacture antenna radios for semiconductor radios, magnetic heads for recorders, memory elements in computers, and iron cores for transformers, alternators, electromagnets, and various high-frequency components. Common metal soft magnetic materials are soft iron, silicon steel, nickel-iron alloy, etc. Common ferrite magnets are manganese zinc ferrite, nickel zinc ferrite and so on. The remanence of hard magnetic materials is strong, and it is not easy to demagnetize. It is suitable for making permanent magnets, and it is used in magnetic electrical instruments, speakers, microphones, permanent magnet motors and other electrical equipment. Common metal hard magnetic materials are carbon steel, tungsten steel, aluminum nickel cobalt alloy, etc. The common hard ferrite is barium ferrite and saw ferrite.
With the progress of society, the relationship between magnetic materials and our daily lives is also getting closer. Tapes used in tape recorders, video tapes used in video recorders, magnetic disks used in electronic computers, and credit cards for deposits contain magnetic materials. These magnetic materials are called magnetic recording materials. With magnetic recording materials, we can store large amounts of information on tapes, video tapes, and magnetic disks, and “read” these information when needed. Magnetic recording materials used magnetic oxides before the 1970s. After the successful development of the alloy magnetic powder in 1978, the use of metallic magnetic materials began, which greatly improved the magnetic recording performance.
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