How to Magnetize a Magnet?
The basic way to magnetize a magnet is using a coil, i.e. an electromagnet, to generate a magnetic field. The generated magnetic field increases as the charging current increases, it drives micro magnetic domains of a magnet rotate to the magnetization direction. When all the micro magnetic domains aligned along the same direction, the magnet is magnetized to the saturation state.
How to Demagnetize a Magnet?
Demagnetizing a magnet is the opposite process of magnetizing a magnet as described above. Just alternative the charging current direction through the coil to generate a reverse magnetic field. The reverse magnetic field or demagnetizing field increases as the charging current increases, more and more micro magnetic domains rotate to the demagnetization direction. When the reverse magnetic field reaches the intrinsic coercivity Hcj point, the magnet is thoroughly demagnetized.
Besides the reverse magnetic field demagnetization method, there is another way to demagnetize a magnet by increasing temperature which is called thermal demagnetization. In the latter way, the aligned micro magnetic domains become unstable as the temperature increases. When the temperature excesses a magnet’s Curie temperature Tc, the whole micro magnetic domains turn to a random orientation state so that the macro magnetic moment is zero. In other words, the magnet is thoroughly demagnetized.