? ? ? ? Magnetic material is an old and widely used functional material of the magnet factory, and the magnetism of material has been recognized and applied as early as 3000 years ago. For example, in ancient China, natural magnets were used as the compass. Modern magnetic materials have been widely used in our daily life, such as the permanent magnetic material is used as the core material used in motor, transformer, magnetic disc memory used as magnetic recording by computer, such as floppy disks.
? ? ? ? It can be said that magnetic materials are closely related to information, automation, mechatronics, national defense and the national economy. It is generally believed that a magnetic material is a substance that produces magnetism directly or indirectly by excessive elements such as iron, cobalt, nickel, and their alloys.