From Thin Films to Nanodots: Bottom-Up Integration of Fe₃O₄ on Nb:STO for Functional Oxide Nanostructures.

Abstract

Epitaxial heterostructures of iron oxide thin films on oxide substrates are promising for spintronic applications. Scaling down such heterostructures into ordered nanostructures enables integration into functional devices. However, fabricating well-ordered nanostructures while retaining their structural and functional integrity remains challenging. A bottom-up approach is used to grow epitaxial Fe₃O₄ nanodot arrays on Nb-doped SrTiO₃(Nb:STO) substrates integrating anodic aluminum oxide (AAO) templates combined with pulsed laser deposition. Following this method, the lateral confinement of Fe₃O₄ into 30 and 70 nm nanodots with 3D long-range ordering is then confirmed by grazing-incidence small-angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM). Building on this structural evidence, the Verwey transition is found to be retained, as observed in the continuous film. To explore its applicability in nanoelectronics, conductive atomic force microscopy (c-AFM) is used to probe local electrical behavior, and reveals bipolar resistive switching at room temperature in individual nanodots, consistent with behavior observed in thin films. Together, these results establish the first demonstration of ordered epitaxial Fe₃O₄/Nb:STO nanodots with preserved structural, magnetic, and electrical functionalities, providing a generalizable route for nanoscale integration of complex oxides.