Exchange bias and its training effect in Ni/NiO nanocomposites

Exchange bias (EB) and EB training effect have been studied in Ni/NiO nanocomposites, in which a negative EB field of about 2.2 kOe at 5 K is achieved in as-milled Ni/NiO powders upon cooling in a field of 10 kOe. The coercivity of the Ni nanoparticles is significantly enhanced by coupling with NiO. The EB training effect is activated by consecutive application of magnetic hysteresis loops. Besides the FM/AFM interfacial interaction and bulk AFM domain-state model, the model presented by Hoffmann may play an important role to induce such a beneficial initial spin configuration for a typical EB training effect system. Furthermore, a phenomenological relaxation model proposed by Binek is used to describe the next spin configurational relaxation process of AFM interface magnetization towards equilibrium.