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Yttrium iron garnet (YIG) and barium titanate (BTO) were co-deposited on (001)-orientated gadolinium gallium garnet substrates by pulsed laser deposition with composition determined by the ratio of laser shots ablating each target. With increasing shot ratios of YIG/BTO = 2.5/1, 4/1, 20/1, and 30/1, the majority phase in the film changes from textured polycrystalline perovskite to epitaxial garnet. Cross-sectional STEM characterization of the YIG-rich films reveals three distinct sublayers: the bottom layer is a coherent epitaxial garnet layer with higher unit cell volume than that of YIG; the second layer is garnet exhibiting crystalline defects and misorientation; and the upper layer is amorphous. Highly defective regions within the second layer are richer in Ba, suggesting that the microstructure is promoted by the insolubility of Ba in YIG. Temperature-dependent magnetization measurements fitted to a super-exchange dilution model indicate the presence of nonmagnetic Ti and vacancies in both octahedral and tetrahedral sites.

 

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.