The exchange bias properties of a granular system composed of $\mathrm{Fe}$ nanoparticles (mean size $\sim 6\mathrm{nm}$) embedded in an $\mathrm{Fe}$ oxide matrix have been studied. The effect of the cooling field on the exchange field, coercivity and remanent magnetization at $T=5\mathrm{K}$ has been investigated. The observed variations are explained in terms of interfacial exchange coupling between a ferromagnetic phase (the $\mathrm{Fe}$ particles) and a disordered magnetic phase (the oxide matrix), whose spin configuration is strongly affected by the cooling field.

• Received 17 March 2004

DOI:https://doi.org/10.1103/PhysRevB.70.052401