To put it simply:
The magnetic permeability and coercivity of various ferromagnetic materials can be judged through the magnetic retention loop. Look at which are soft magnetic materials and which are hard magnetic materials.
Soft magnetic materials are easy to magnetize and demagnetize. They are suitable for repeated magnetization. They can be used to make iron cores for transformers, relays, electromagnets, motors and various high-frequency components.
Ferromagnetic materials such as carbon steel, tungsten steel, and Al-Ni-Co alloys are not too high in permeability, but they have high coercive force and large remanence, and the hysteresis loop is wide and short. Hard magnetic materials can retain a large remanence after magnetization, and are not easy to demagnetize, suitable for making permanent magnets. Like magnetoelectric instruments, earphones, small DC motors and so on.