Magnetic materials, generally referred to as strong magnetic materials, are ancient and widely used functional materials. The magnetism of materials was known and used as early as 3000 years ago. For example, natural magnets were used as compass in ancient China. Modern magnetic data are widely used in our daily life, such as permanent magnetic data used as motor, core data used in transformer, magnetic disc used as memory, magnetic recording floppy disk used in computer, etc.
In big bit information, magnetic materials are closely related to information technology, automation, mechatronics, national defense and national economy. It is generally believed that magnetic materials are those materials which can be directly or indirectly magnetized by transition elements such as iron, cobalt, nickel and their alloys. According to the difficulty of demagnetization after magnetization, magnetic materials can be divided into soft magnetic data and hard magnetic data. After magnetization, the material with simple demagnetization is called soft magnetic data, and the material with non simple demagnetization is called hard magnetic data. Generally speaking, the remanence of soft magnetic data is smaller than that of hard magnetic data.
Experiments show that any material can be magnetized more or less in the external magnetic field, but the degree of magnetization is different. According to the characteristics of matter in the external magnetic field, matter can be divided into five categories: paramagnetic matter, diamagnetic matter, ferromagnetic matter, ferromagnetic matter and diamagnetic matter.
According to the molecular current hypothesis, matter should show similar characteristics in the magnetic field, but it tells us that the characteristics of matter in the external magnetic field are very different. This reflects the limitation of molecular current hypothesis. In fact, there are differences in the microstructure of various materials, which is the reason for the differences in magnetic properties.
We call paramagnetic material and diamagnetic material weak magnetic material and ferromagnetic material strong magnetic material.
Generally speaking, magnetic materials refer to strong magnetic materials. According to the difficulty of demagnetization after magnetization, magnetic materials can be divided into soft magnetic materials and hard magnetic materials. After magnetization, the material with simple demagnetization is called soft magnetic material, and the material without simple demagnetization is called hard magnetic material. Generally speaking, the remanence of soft magnetic materials is smaller than that of hard magnetic materials.