Modification of Electrical and Magnetic Properties of Fe₃O₄ Epitaxial Thin Films by Nitrogen Substitution for Oxygen

Epitaxial thin films of nitrogen-substituted Fe3O4 (Fe3O4–yNy) were synthesized on MgO (001) substrates by using nitrogen-plasma-assisted pulsed laser deposition. The obtained Fe3O4–yNy thin films showed ferrimagnetic behavior at room temperature. The carrier density of the films was decreased by nitrogen substitution up to y = 0.4. These properties were similar to those of A-site (tetrahedral site)-substituted Fe3O4, such as ZnxFe3–xO4 or MnxFe3–xO4, previously reported. On the other hand, the electrical resistivity of the Fe3O4–yNy thin films at room temperature was rather insensitive to y, in sharp contrast to ZnxFe3–xO4 or MnxFe3–xO4, of which the resistivity drastically increased with increase of x. These results indicated that nitrogen substitution is an effective method to control the carrier density of Fe3O4 without disturbing the carrier conduction through the B-site (octahedral site) Fe ion network. Density functional theory-based first-principles calculation predicted that Fe3O4–yNy is half-metallic.