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

Biphasic, nanostructured NiFe 2 O 4 /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 SiO 2 /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 NiFe 2 O 4 and NiO. H E and H C increased with NiO content, which may be explained by a concomitant increase in NiFe 2 O 4 /NiO interfacial density. Large H E (∼250 Oe) and H C (∼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.