Bulk Single Crystal-Like Structural and Magnetic Characteristics of Epitaxial Spinel Ferrite Thin Films with Elimination of Antiphase Boundaries

Spinel ferrite NiFe₂O₄ thin films have been grown on three isostructural substrates, MgAl₂O₄, MgGa₂O₄, and CoGa₂O₄ using pulsed laser deposition. These substrates have lattice mismatches of 3.1%, 0.8%, and 0.2%, respectively, with NiFe₂O₄. As expected, the films grown on MgAl₂O₄ substrate show the presence of the antiphase boundary defects. However, no antiphase boundaries (APBs) are observed for films grown on near-lattice-matched substrates MgGa₂O₄ and CoGa₂O₄. This demonstrates that by using isostructural and lattice-matched substrates, the formation of APBs can be avoided in NiFe₂O₄ thin films. Consequently, static and dynamic magnetic properties comparable with the bulk can be realized. Initial results indicate similar improvements in film quality and magnetic properties due to the elimination of APBs in other members of the spinel ferrite family, such as Fe₃O₄ and CoFe₂O₄, which have similar crystallographic structure and lattice constants as NiFe₂O₄.

Antiphase boundary defects in epitaxial nickel ferrite thin films are eliminated by using spinel substrates which have a small lattice mismatch with the films. Consequently, bulk single crystal nickel ferrite-like magnetic and microwave properties are obtained in the films. Magnetite and cobalt ferrite also show similar improvements in thin film quality and properties.

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