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This work characterizes the structural, magnetic, and ferroelectric properties of epitaxial LuFeO₃orthoferrite thin films with different Lu/Fe ratios. LuFeO₃thin films are grown by pulsed laser deposition on SrTiO₃substrates with Lu/Fe ratio ranging from 0.6 to 1.5. LuFeO₃is antiferromagnetic with a weak canted moment perpendicular to the film plane. Piezoresponse force microscopy imaging and switching spectroscopy reveal room temperature ferroelectricity in Lu‐rich and Fe‐rich films, whereas the stoichiometric film shows little polarization. Ferroelectricity in Lu‐rich films is present for a range of deposition conditions and crystallographic orientations. Positive‐up‐negative‐down ferroelectric measurements on a Lu‐rich film yield ≈13 µC cm⁻²of switchable polarization, although the film also shows electrical leakage. The ferroelectric response is attributed to antisite defects analogous to that of Y‐rich YFeO₃, yielding multiferroicity via defect engineering in a rare earth orthoferrite.

 

Abstract Single-phase multiferroic materials that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, motivating an ongoing search for mechanisms for unconventional ferroelectricity in magnetic oxides. Here, we report an antisite defect mechanism for room temperature ferroelectricity in epitaxial thin films of yttrium orthoferrite, YFeO 3 , a perovskite-structured canted antiferromagnet. A combination of piezoresponse force microscopy, atomically resolved elemental mapping with aberration corrected scanning transmission electron microscopy and density functional theory calculations reveals that the presence of Y Fe antisite defects facilitates a non-centrosymmetric distortion promoting ferroelectricity. This mechanism is predicted to work analogously for other rare earth orthoferrites, with a dependence of the polarization on the radius of the rare earth cation. Our work uncovers the distinctive role of antisite defects in providing a mechanism for ferroelectricity in a range of magnetic orthoferrites and further augments the functionality of this family of complex oxides for multiferroic applications. 

Physical neural networks made of analog resistive switching processors are promising platforms for analog computing. State-of-the-art resistive switches rely on either conductive filament formation or phase change. These processes suffer from poor reproducibility or high energy consumption, respectively. Herein, we demonstrate the behavior of an alternative synapse design that relies on a deterministic charge-controlled mechanism, modulated electrochemically in solid-state. The device operates by shuffling the smallest cation, the proton, in a three-terminal configuration. It has a channel of active material, WO₃. A solid proton reservoir layer, PdH_x, also serves as the gate terminal. A proton conducting solid electrolyte separates the channel and the reservoir. By protonation/deprotonation, we modulate the electronic conductivity of the channel over seven orders of magnitude, obtaining a continuum of resistance states. Proton intercalation increases the electronic conductivity of WO₃by increasing both the carrier density and mobility. This switching mechanism offers low energy dissipation, good reversibility, and high symmetry in programming.

 

YFeO₃thin films are a recent addition to the family of multiferroic orthoferrites where Y_Feantisite defects and strain have been shown to introduce polar displacements while retaining magnetic properties. Complete control of the multiferroic properties, however, necessitates knowledge of the defects present and their potential role in modifying behavior. Here, the structure and chemistry of antiphase boundaries in Y‐rich multiferroic YFeO₃thin films are reported using aberration corrected scanning transmission electron microscopy combined with atomic resolution energy dispersive X‐ray spectroscopy. It is found that Fe_Yantisites, which are not stable in the Y‐rich film bulk, periodically arrange along antiphase boundaries due to changes in the local structural environment. Using density functional theory, it is shown that the antiphase boundaries are polar and bi‐stable, where the presence of Fe_Yantisites significantly decreases the switching barrier. These results highlight how planar defects, such as antiphase boundaries, can stabilize point defects that would otherwise not be expected to form within the structure.