Abstract
Three samples of naturally mixed Ni (>120 nm) and NiO (similar to 10 nm) were prepared with different particle diameters/distributions and amount of metallic nickel. Exchange bias effect has been observed and strongly depends upon both particle sizes/distributions and concentration of Ni, achieving the highest value (similar to 2200 Oe at 5 K) for the pure NiO, while the corresponding value for the sample with maximum Ni concentration is similar to 70 Oe. This is tentatively explained taking into account the effect of induced dipolar field by bigger Ni particles on the stabilization of magnetically ordered surface regions of the smaller NiO nanoparticles.