# Hysteresis

The typical but exaggerated hysteresis behavior of a ferromagnetic material is shown in the figure below, where the magnetic induction B is plotted vs. the magnetic field intensity H, which is directly proportional to the current in the surrounding coil. The horizontal axis could equally well be labeled I" instead of H". The "0" is the non-magnetized or demagnetized state (B=0, I=0) which can be reached by applying an alternating current and slowly reducing its amplitude to zero. As the current increases from the demagnetized state, the B value lags behind what one might expect and follows the curve to (a') and toward saturation at (a). With large variations in I, the behavior follows a major loop (abcdefa...); while for small variations in I, the behavior follows a minor loop (a'b'c'd'e'f'a'...) or (a'b'a'...) if the current I never becomes negative. Certain points of a hysteresis loop have names: Br is the remanent value at I = 0 after the material is saturated at (a.) Hc is the coercive field or the coercivity ( i.e. the H or I required to reduce B to zero).