Steel or other materials can become permanent magnets because after proper treatment and processing, the internal non-uniformity is in the best state and the Coercivity is the largest. The inhomogeneity of iron crystal structure, internal stress, etc. is very small, and the Coercivity is naturally very small. It does not need a strong magnetic field to magnetize or demagnetize it, so it cannot become a permanent magnet. Materials that are easily magnetized and demagnetized are usually referred to as "soft" magnetic materials. 'Soft' magnetic materials cannot be used as permanent magnets, iron belongs to this type of material

The application range of permanent magnets is diverse, including televisions, speakers, audio speakers, radios, leather bag buckles, data cable magnetic rings, computer hard drives, mobile phone vibrators, and so on. Permanent magnets such as loudspeakers use the principle of electric coils moving in a magnetic field to produce sound. The permanent magnet on the horn utilizes the magnetic field generated by the current in the coil to interact with it, causing the relative position of the coil and magnet to change, causing the paper bowl on the horn to vibrate, pushing air and spreading this vibration, allowing the human ear to hear sound. In short, permanent magnets are ubiquitous in people's lives, making it convenient for our production and daily life.