Magnetization reversal in polycrystalline NiO-Co exchange anisotropy coupled bilayers

Real time investigation of magnetization reversal in exchange anisotropy co upled polycrystalline NiO-Co bilayers show that reversal in exchange couple d Co films is highly local and nonuniform in nature. Growth of reversed dom ains occur primarily by the abrupt nucleation and coalescence of new revers ed domains; wall motion, although observable, is not the dominant growth mo de for reversed domains. Clear evidence is presented which shows that the s trength of the exchange field varies at the microscopic scale across the sa mple. This manifests itself as different microscopic regions switching abru ptly at different fields, and a given area switching at different fields in the positive and negative field directions due to the unidirectional rathe r than uniaxial nature of exchange anisotropy. (C) 2000 American Institute of Physics. [S0021-8979(00)60408-5].