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coercive force[kō′ər·siv ′fȯrs]
one of the characteristics of the phenomenon of hysteresis. In magnetic hysteresis the coercive force is the magnetic field intensity at which a ferromagnetic specimen that has been initially magnetized to saturation becomes demagnetized. A distinction is made between the coercive force JHc (or Hc) and the force BHc, when the magnetization J of the specimen or the magnetic induction B in the specimen becomes zero.
Coercive forces are measured by means of coercimeters. The values for ferromagnetic materials vary over a wide range, from 10-3 to 104 oersteds, or 8 x 10-2 to 8 x 105 amperes per meter (A/m). For a given magnetic material the coercive force depends to a large extent on the preparation of the specimen and on its treatment, as well as on external conditions, such as temperature. According to the magnitude of the coercive force, magnetic materials are customarily divided into magnetically soft materials (small Hc) and magnetically hard materials (large Hc). The value of the coercive force is determined by the factors that oppose remagnetization of the specimen. The presence of impurities, lattice defects, and various types of inhomogeneities in a specimen hinders the movement of domain walls and thus increases Hc.
Particularly high values of coercive force (103–104 oersteds) are achieved by single-domain ferromagnetic particles (with substantial magnetic anisotropy). The coercive force of ferroelectric materials is considered to be like that of ferromagnetic materials.