Metals such as iron, nickel, and cobalt belong to ferromagnetism, and their atomic structures are unique.

In addition, ferromagnetic materials also have the following characteristics:

As the external magnetic field B increases, the internal B '' of the medium also increases, but B '' does not have a linear relationship with B, as mentioned above μ Not a constant. When saturation is reached, B '' hardly increases, which is called magnetic saturation.

Once ferromagnetic material is magnetized and the external magnetic field is removed, it still retains some of its magnetism, which is called remanence (some artificial magnets use the principle of greater remanence). When the intensity of the reverse magnetic field reaches H. At this time, B in the iron core is equal to zero, and the magnetic field strength H is at this point. It is called coercive force.

If ferromagnetic material is heated, when its temperature is above a critical temperature T. At the critical temperature of ferromagnetic phase transition, known as the Curie point, it transforms into paramagnetic material. We will talk about the principles later on