1. What are magnetic materials?
Materials will be magnetized under the action of an external magnetic field to produce certain characteristic magnetic properties. If the material is magnetized under the action of an external magnetic field and can maintain constant strong magnetism for a long time when the external magnetic field is removed, it is called a permanent magnet material or a hard magnetic material. If the magnetic properties change as the magnetic field changes, it is called a soft magnet. To sum up, magnetic materials can be divided into hard magnetic materials (permanent magnets) and soft magnets.
2. Main properties of permanent magnet materials
1) Residual magnetism
After the external magnetic field is magnetized, the magnetic induction intensity value of the permanent magnet material is obtained when the external magnetic field is removed and reaches zero.
2) Coercive force
When the permanent magnet material is magnetized to saturation magnetization and a reverse magnetic field is applied, the reverse magnetic field intensity required when the residual magnetization induction intensity of the permanent magnet material drops to zero.
3) Magnetic energy product
The maximum value of the magnetic field energy provided by the permanent magnet material to the external magnetic circuit. Remember that the size of the magnetic energy product directly indicates the performance of the magnet. The number of the grade of NdFeB permanent magnet material and Samarium Cobalt permanent magnet material is the maximum magnetic energy product.
3. History of permanent magnet materials
Our country's literature records can verify that China has a long history of using permanent magnetic materials. As early as the Spring and Autumn Period and the Warring States Period, Sinan made of natural permanent magnetic materials (ferric oxide) was used for guides to identify directions. It was later developed into a compass. By the Song Dynasty it already used in navigation. At present, no physical objects have been unearthed in archaeological excavations, but it can be verified that China has discovered the properties of permanent magnet materials very early and applied them in daily life practice.