Permanent magnetic materials (hard magnetic materials) refer to ferromagnetic materials with large hysteresis loops, low permeability, high remanence, high coercivity and high magnetoresistance. Hard magnetic materials are difficult to magnetize and demagnetize, such as tungsten steel, ferrite, neodymium-iron-boron, etc. These materials are easy to magnetize and difficult to demagnetize. They are mainly used as tape materials and permanent magnets. Soft magnetic materials refer to ferromagnetic materials with narrow hysteresis loops, high permeability, low remanence, low coercivity and low magnetoresistance. Soft magnetic materials are easy to magnetize and demagnetize, such as silicon steel sheet, ferronickel alloy, cast steel, etc. These materials have high permeability, easy magnetization, easy demagnetization, small area surrounded by hysteresis loops and low hysteresis loss. They are mostly used as magnet heads and motor cores.
The hysteresis loop reflects the magnetization of ferromagnet. The hysteresis loop is a closed curve of the relationship between the magnetic induction intensity and the magnetic field intensity produced by ferromagnetic materials under the action of an external alternating magnetic field.