Magnetic hysteresis: When a magnetic material is subjected to cycle of magnetization, it is found that flux density (B) in the material lags behind applied magnetizing force (H). This phenomenon is known as magnetic hysteresis.
Cause: This is due to non-linear relationship between magnetic field intensity and magnetic flux density. When we attempt to produce magnetic field through magnetic material, the domains orient along the direction of field. The magnetic material has tendency to oppose the movement of orientation, due to which the flux density lags behind the magnetic field intensity.