Enhanced exchange bias and coercivity arising from heterojunctions in Ni-NiO nanocomposites.

By a reflux process, we prepared Ni-NiO nanocomposites that are face-centered cubic (fcc). By tuning the precursor concentration, we controlled the Ni content in the Ni-NiO nanocomposites. We found that both the interface of Ni and NiO crystal lattices and the weight fraction of Ni have significant impacts on their magnetic properties. There is increase of saturation magnetization and decrease of coercivity (H-C) with the increase of the Ni weight fraction. Large exchange bias (H-E) and enhanced H-C are observed at 5 K, which are due to the creation of heterojunctions at the interfaces of ferromagnetic Ni and antiferromagnetic NiO. After optimization, it is observed that the Ni-NiO nanocomposites with an Ni content of 2.6% show an H-C and H-E of 1068 and 350 Oe, respectively.