Lagging of the magnetization of ferromagnetic material (see ferromagnetism ), such as iron , behind variations of the magnetizing field.
When such a material is placed in a coil of wire carrying an electric current , the magnetic field so created forces atoms in the material to align with the field. This increases the total magnetic field to a maximum when all the atoms are aligned, though the total field lags behind the magnetizing field. When the intensity of the magnetizing field is decreased to zero, some field remains in the material, and if the magnetizing field is reversed the total magnetization also reverses but again lags behind. The complete cycle, known as a hysteresis loop, dissipates energy in the form of heat as the magnetization is reversed.