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1. Polarization pinning at antiphase boundaries in multiferroic YbFeO ₃

   https://doi.org/10.1088/1674-1056/ad8cbc  

   Ren, Guodong; Omprakash, Pravan; Li, Xin; Yun, Yu; Thind, Arashdeep S; Xu, Xiaoshan; Mishra, Rohan (November 2024, Chinese Physics B)

   Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO₃. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO₃thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO₆octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO₆octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains. 

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2. Emergent Ferromagnetism at LaFeO ₃ /SrTiO ₃ Interface Arising from a Strain‐Induced Spin‐State Transition

   https://doi.org/10.1002/admi.202500169  

   Zhu, Menglin; Lanier, Joseph; Genlik, Sevim Polat; Flores, Jose G; Barbosa, Victor_da_Cruz Pinha; Randeria, Mohit; Woodward, Patrick M; Ghazisaeidi, Maryam; Yang, Fengyuan; Hwang, Jinwoo (July 2025, Advanced Materials Interfaces)

   Abstract Creating new interfacial magnetic states with desired functionalities is attractive for fundamental studies and spintronics applications. The emergence of interfacial magnetic phases demands the fabrication of pristine interfaces and the characterization and understanding of atomic structure as well as electronic, magnetic, and orbital degrees of freedom at the interface. Here, a novel interfacial insulating ferromagnetic order in epitaxial films of LaFeO₃grown on SrTiO₃ characterized by a combination of electron microscopy and spectroscopy, magnetometry, and density functional theory, is reported. The epitaxial strain drives a spin‐state disproportionation in the interfacial layer of LaFeO₃, which leads to a checkerboard arrangement of low‐ and high‐spin Fe³⁺ions inside smaller and larger FeO₆octahedra, respectively. Ferromagnetism at the interface arises from superexchange interactions between the low‐ and high‐spin Fe³⁺. Moving away from the interface the structure relaxes and the antiferromagnetic order seen in bulk LaFeO₃is restored. It demonstrates how strain‐induced spin‐state disproportionation at the interface creates a novel ferromagnetic superexchange interaction in magnetic insulators, offering a new pathway to engineer interfacial magnetism for spintronic applications. 

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3. Recent progress on multiferroic hexagonal rare-earth ferrites (h-RFeO ₃ , R = Y, Dy-Lu)

   https://doi.org/10.1088/1361-6463/ad97c5  

   Li, Xin; Yun, Yu; Xu, Xiaoshan (December 2024, Journal of Physics D: Applied Physics)

   Abstract Multiferroic hexagonal rare-earth ferrites (h-RFeO₃, R= Sc, Y, and rare earth), in which the improper ferroelectricity and canted antiferromagnetism coexist, have been advocated as promising candidates to pursue the room-temperature multiferroics, because of strong spin-spin interaction. The strong interactions between the ferroic orders and the structural distortions are appealing for high-density, energy-efficient electronic devices. Over the past decade, remarkable advances in atomic-scale synthesis, characterization, and material modeling enable the significant progresses in the understanding and manipulation of ferroic orders and their couplings in h-RFeO₃thin films. These results reveal a physical picture of rich ferroelectric and magnetic phenomena interconnected by a set of structural distortions and spin-lattice couplings, which provides guidance for the control of ferroic orders down to the nano scale and the discovery of novel physical phenomena. This review focus on state-of-the-art studies in complex phenomena related to the ferroelectricity and magnetism as well as the magnetoelectric couplings in multiferroic h-RFeO₃, based on mostly the recent experimental efforts, aiming to stimulate fresh ideas in this field. 

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4. Persistent structural distortion for anticipated improper ferroelectricity in ultrathin h-Lu _{1− x} Ca _x MnO ₃ films

   https://doi.org/10.1088/1361-648X/ae3653  

   Yang, Detian; Liu, Yaohua; Zhou, Haidong; N’Diaye, Alpha T; Xu, Xiaoshan (January 2026, Journal of Physics: Condensed Matter)

   Abstract Improper ferroelectricity in hexagonal rare-earth manganites (h-RMnO₃, R = Ho–Lu, Y, Sc) arises from a geometric distortion as the primary order parameter, resilient to depolarizing fields and promising for ultrathin ferroelectric devices. However, the substrate-induced interface clamping effect, which suppresses the geometric distortion in the sub-nanometer regime, has thus far hindered the realization of two-dimensional improper ferroelectrics. This study demonstrates that doping with calcium can enhance ferroelectric structural distortion in h-LuMnO₃thin films. Compressively strained h-Lu_1−xCa_xMnO₃(x= 0.1, 0.2, 0.3, 0.4, 0.5) epitaxial thin films were stabilized on sapphire substrates using an h-ScFeO₃buffer layer. We have found that the interface clamping effect is entirely overcome when the doping concentration reachesx⩾ 0.2, establishing a potential quasi-2D ferroelectric system with a remarkably high estimated structural transition temperature of larger than 1200 K inferred indirectly from temperature-resolved reflection high-energy electron diffraction. This finding suggests a general strain engineering strategy to enhance improper ferroelectricity in hexagonal manganites. 

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5. Electron and Spin Delocalization in [Co ₆ Se ₈ (PEt ₃ ) ₆ ] ^0/+1 Superatoms

   https://doi.org/10.1002/cphc.202300064  

   Xu, Yunyao; Chen, Jia; Aydt, Alexander P.; Zhang, Lichirui; Sergeyev, Ivan; Keeler, Eric G.; Choi, Bonnie; He, Shoushou; Reichman, David R.; Friesner, Richard A.; et al (January 2024, ChemPhysChem)

   ChemPhysChem (Ed.)

   Abstract Molecular clusters can function as nanoscale atoms/superatoms, assembling into superatomic solids, a new class of solid‐state materials with designable properties through modifications on superatoms. To explore possibilities on diversifying building blocks, here we thoroughly studied one representative superatom, Co₆Se₈(PEt₃)₆. We probed its structural, electronic, and magnetic properties and revealed its detailed electronic structure as valence electrons delocalize over inorganic [Co₆Se₈] core while ligands function as an insulated shell.⁵⁹Co SSNMR measurements on the core and³¹P,¹³C on the ligands show that the neutral Co₆Se₈(PEt₃)₆is diamagnetic and symmetric, with all ligands magnetically equivalent. Quantum computations cross‐validate NMR results and reveal degenerate delocalized HOMO orbitals, indicating aromaticity. Ligand substitution keeps the inorganic core nearly intact. After losing one electron, the unpaired electron in [Co₆Se₈(PEt₃)₆]⁺¹is delocalized, causing paramagnetism and a delocalized electron spin. Notably, this feature of electron/spin delocalization over a large cluster is attractive for special single‐electron devices. 

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