Exchange bias effect in NiO/NiFe2O4 nanocomposites

Abstract

A series of (100−x)NiO/(x)NiFe2O4 nanocomposites (x = 0, 2.5, 5, 8.3, 12.5, 25) synthesized by a chemical coprecipitation method have been investigated. The exchange bias field HE of the nanocomposites reaches a maximum at x = 2.5, and then decreases with increasing x. The decrease of HE is attributed to the formation of isolated ferrimagnetic NiFe2O4 clusters, which is confirmed by observation with the use of high resolution transmission electron microscopy. The temperature dependence of HE and the coercivity HC for pure NiO is different from those with other samples, which is due to the exchange coupling between the uncompensated antiferromagnetic core and disordered surface shell of NiO nanoparticles.