Microplasma-Based Growth of Biphasic NiFe2O4/NiO Nanogranular Films for Exchange Bias Applications

Biphasic, nanostructured NiFe2O4/NiO films exhibiting exchange bias were synthesized using high-pressure microplasma based deposition. Organometallic Ni and Fe precursors were dissociated via electron impact in the hollow cathode region of a supersonic plasma jet with oxygen to form a directed flux of Ni and Fe oxide species that were subsequently spray deposited on SiO2/Si substrates to form nanostructured thin films. Exchange bias (H-E) and coercivity (H-C) enhancement were observed for all films containing NiO after field cooling indicating an exchange interaction between NiFe2O4 and NiO H-E and H-C increased with NiO content, which may be explained by a concomitant increase in NiFe2O4/NiO interfacial density. Large H-E (similar to 250 Oe) and H-C (similar to 700 Oe) were measured at 20 K, and exchange bias persisted at high temperatures (305 K) where an H-E and H-C of 80 and 400 Oe were observed, respectively.