Enhanced magnetic-field tunability of the Verwey transition in tailor-made magnetite thin films

Abstract Magnetite (Fe 3 O 4 ) is a material of ongoing interest in solid state physics due to its enigmatic Verwey transition, while being extensively studied as thin film for spintronic applications. Here, we report on our study of the Verwey transition under magnetic fields in Fe 3 O 4 thin films on spinel substrates Co 2−x−y Mn x Fe y TiO 4 and non-magnetic Mg 2 TiO 4 . The Verwey transition of these films is highly tunable and anisotropic with applied magnetic fields suggesting strong magnetostriction via an active spin-orbit effect of the Fe 2+ ions. An alteration of Fe 2+ orbital occupations, however, does not impede the Verwey transition, while tensile strain enhances its transition temperature. This indicates that various types of orbital orderings may occur depending on the thin film conditions. Remarkably, this high magnetic tunability results in a closed magnetoresistance-loop reaching up to 88% at 0.5 Tesla, which is beyond one order of magnitude larger than the reported values of Fe 3 O 4 films. Additionally, the spin-polarized tunneling channel for the magnetoresistance is active in anti-phase boundary-free Fe 3 O 4 /Mg 2 TiO 4 thin films. These findings underscore the critical role of utilizing structural defect-free, high-quality thin films in exploring the full potential of Fe 3 O 4 thin films, offering additional perspectives for understanding the Verwey transition of Fe 3 O 4 .