The coercive force of a permanent magnet is equal to the demagnetizing force required to reduce the residual induction to zero in a magnetic field after magnetizing to saturation, measured in oersteds or A/m, denoted as Hc or Hcb.That is, when the external applied demagnetizing field exactly reaches Hcb , the magnet has no apparent magnetic flux any more.

Equation (1-1) indicates, when H=Hcb, B=0 and J=-μ0Hcb. As any value of J or B on the second quadrant of demagnetization curve must be less than Br or Jr, μ0Hcb  must thus be small than Br or Jr  in absolute value. For example, when a permanent magnet has a remanence Br =12.3 kGs, then its coercive force  Hcb cannot be greater than 12.3 kOe.