Magnetic Properties of Zn-Ferrites Obtained From Multilayer Film Deposited by Sputtering

Epitaxial ZnFe₂O₄ thin films were deposited on monocrystalline MgO substrate by dc-sputtering. Ferrites were grown from Zn-O and Fe-O multilayers starting from metallic targets in oxygen atmosphere. The number and thickness of layers were varied holding constant the total thickness (50 nm) and sample stoichiometry (Fe/Zn=2). The samples were structural and magnetically characterized by X-ray diffraction and magnetic measurements, respectively. Thin film fabricated using 20 bilayers of thickness 3 nm present a magnetic behavior similar to bulk ZnFe₂O₄, with a Néel temperature T_N=10.5 K. The magnetic behavior of those films obtained from thicker bilayers (6 and 10 nm) is characterized by the coexistence of antiferro and ferromagnetic regions. This is probably due to the inhomogeneities in Zn and Fe distributions caused by an incomplete interdiffusion process prevented by the relatively large multilayer thickness. These inhomogeneities probably generate zinc-iron position replacements and interrupt the long-range antiferromagnetic order, giving rise to ferromagnetic clusters coexisting with the antiferromagnetic component.