摘要
γ-Fe2O3 particles, surface modified with NiO crystallites, form a unique nanocomposite that points to how to tune strong interfacial exchange coupling. We find that Ni2+ migrates into the octahedral sites of the γ-Fe2O3 nanoparticle surface, and this NiFe2O4-like layer permits effective magnetic coupling of Ni and Fe sites that strengthens the interface exchange. A large increase in coercivity coinciding with a loss of exchange bias is achieved by this strong interfacial coupling that results in a Ni2+ moment reversal in the NiO with the γ-Fe2O3. This work reveals the importance of intermixing in, and possibility to use, such an exchange coupling regime to alter substantially the coercivity and hence control an important property of exchange-coupled nanocomposite magnets.