Magnetoresistance of epitaxial and polycrystalline Fe₃O₄ films near Verwey transition

We report investigations of magnetoresistance (MR) in epitaxial and polycrystalline Fe₃O₄ films. MR in epitaxial Fe₃O₄ films exhibits a local maximum at T_V and a large value of -20% at 60 K. Based on a 1D half infinite spin chain model, the fitting parameter, which depends on the volume fraction of electronic scattering boundaries, sharply increases below T_V with the decreased temperature. We suppose that the twin boundaries formed below T_V facilitate the increase in MR and can act as antiphase boundaries (APBs) where the magnetic moments across twin boundaries are coupled antiferromagnetically. Similar MR behavior in Fe₃O₄(100) and (111) epitaxial films manifests the independence of MR on the spatial distribution of APBs. The outline of normalized MR in the epitaxial films shows a distinct temperature dependence. The temperature dependence may result from the different electronic transport mechanisms in Fe₃O₄ films. In a polycrystalline Fe₃O₄ film, MR comes from the disordered distribution of magnetic moments at grain boundaries. The effects of APBs, twin boundaries, and grain boundaries on MR are discussed in detail.