Editing Coercivity (section)

==Theory==
At the coercive field, the [[vector (geometry)|vector component]] of the magnetization of a ferromagnet measured along the applied field direction is zero.  There are two primary modes of [[magnetization reversal]]: [[single domain (magnetic)|single-domain]] rotation and [[Domain wall (magnetism)|domain wall]] motion. When the magnetization of a material reverses by rotation, the magnetization component along the applied field is zero because the vector points in a direction orthogonal to the applied field. When the magnetization reverses by domain wall motion, the net magnetization is small in every vector direction because the moments of all the individual domains sum to zero.  Magnetization curves dominated by rotation and [[magnetocrystalline anisotropy]] are found in relatively perfect magnetic materials used in fundamental research.<ref>{{harvnb|Genish|Kats|Klein|Reiner|2004}}</ref> Domain wall motion is a more important reversal mechanism in real engineering materials since defects like [[grain boundary|grain boundaries]] and [[impurity|impurities]] serve as [[nucleation]] sites for reversed-magnetization domains.  The role of domain walls in determining coercivity is complicated since defects may ''pin'' domain walls in addition to nucleating them.  The dynamics of domain walls in ferromagnets is similar to that of grain boundaries and [[plasticity (physics)|plasticity]] in [[metallurgy]] since both domain walls and grain boundaries are planar defects.{{citation needed|date=January 2021}}