Magnetotransport properties of Fe_3O_4 epitaxial thin films: Thickness effects driven by antiphase boundaries

摘要

We present an in-depth study of the magnetotransport properties of epitaxial Fe_3O_4 films as a function of film thickness. The films, grown on α-Al_2O_3(0001) single crystals by atomic-oxygen assisted molecular beam epitaxy, exhibit high structural order and abrupt interfaces. These films contain antiphase boundaries (APBs), the density of which is strongly dependent on film thickness. A series of resistivity and magnetoresistance measurements demonstrate a systematic evolution of these properties with decreasing film thickness, revealing the impact of APBs on the transport properties in the films. We present a model based on the spin-polarized transport across an antiferromagnetically coupled APB in order to successfully reproduce our experimental data over a large range of applied magnetic fields. The comparison of this model with experimental results further clarifies the mechanism of the anomalous magnetotransport behavior in Fe_3O_4.