The coercive force is the amount of magnetising force needed to remove residual magnetism.
To complete the loop, the magnetizing force H is raised in reverse until saturation is reached (point ‘d’), at which point the curve follows the route cd. H is lowered to zero once again, and the curve takes the route de. The residual magnetism is represented by oe. Then, by moving the reversible switch to position ‘1′ and increasing the current flow in the solenoid, H is increased in a positive direction. The loop is completed when the curve follows the route of efa. The magnetizing force is used once again to remove the remaining magnetism oe.
As a result, cf is the total coercive force needed to remove residual magnetism in one cycle of magnetization.
Because hysteresis means “to lag behind,” and because flux density B always lags behind the magnetizing force, H, the loop (abcdefa) produced is termed a hysteresis loop.