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Domain boundaries in ferroic materials are found to have various physical properties not observed in the surrounding domains. Such differences can be enhanced and bring promising functionalities when centrosymmetric nonpolar materials encounter polar domain boundaries. In this work, a tunable polar domain boundary is discovered in an antiferroelectric single crystal. Under a small stress or electric field, the density, volume, and polarity of the boundaries are successfully controlled., (© 2023 Wiley-VCH GmbH.)

Oxide nanosprings have attracted many research interests because of their anticorrosion, high-temperature tolerance, oxidation resistance, and enhanced-mechanic-response from unique helix structures, enabling various applications like nanomanipulators, nanomotors, nanoswitches, sensors, and energy harvesters. However, preparing oxide nanosprings is a challenge for their intrinsic lack of elasticity. Here, an approach for preparing self-assembled, epitaxial, ferroelectric nanosprings with built-in strain due to the lattice mismatch in freestanding La 0.7 Sr 0.3 MnO 3 /BaTiO 3 (LSMO/BTO) bilayer heterostructures is developed. It is found that these LSMO/BTO nanosprings can be extensively pulled or pushed up to their geometrical limits back and forth without breaking, exhibiting super-scalability with full recovery capability. The phase-field simulations reveal that the excellent scalability originates from the continuous ferroelastic domain structures, resulting from twisting under co-existing axial and shear strains. In addition, the oxide heterostructural springs exhibit strong resilience due to the limited plastic deformation nature and the built-in strain between the bilayers. This discovery provides an alternative way for preparing and operating functional oxide nanosprings that can be applied to various technologies., (© 2022 Wiley-VCH GmbH.)

Self-assembled membranes with periodic wrinkled patterns are the critical building blocks of various flexible electronics, where the wrinkles are usually designed and fabricated to provide distinct functionalities. These membranes are typically metallic and organic materials with good ductility that are tolerant of complex deformation. However, the preparation of oxide membranes, especially those with intricate wrinkle patterns, is challenging due to their inherently strong covalent or ionic bonding, which usually leads to material crazing and brittle fracture. Here, wrinkle-patterned BaTiO 3 (BTO)/poly(dimethylsiloxane) membranes with finely controlled parallel, zigzag, and mosaic patterns are prepared. The BTO layers show excellent flexibility and can form well-ordered and periodic wrinkles under compressive in-plane stress. Enhanced piezoelectricity is observed at the sites of peaks and valleys of the wrinkles where the largest strain gradient is generated. Atomistic simulations further reveal that the excellent elasticity and the correlated coupling between polarization and strain/strain gradient are strongly associated with ferroelectric domain switching and continuous dipole rotation. The out-of-plane polarization is primarily generated at compressive regions, while the in-plane polarization dominates at the tensile regions. The wrinkled ferroelectric oxides with differently strained regions and correlated polarization distributions would pave a way toward novel flexible electronics., (© 2020 Wiley-VCH GmbH.)

The voltage modulation of yttrium iron garnet (YIG) is of practical and theoretical significance; due to its advantages of compactness, high-speed response, and energy efficiency, it can be used for various spintronic applications, including spin-Hall, spin-pumping, and spin-Seebeck effects. In this study, a significant ferromagnetic resonance change is achieved within the YIG/Pt bilayer heterostructures uisng ionic modulation, which is accomplished by modifying the interfacial magnetism in the deposited "capping" platinum layer. With a small voltage bias of 4.5 V, a large ferromagnetic field shift of 690 Oe is achieved in heterostructures of YIG (13 nm)/Pt (3 nm)/(ionic liquid, IL)/(Au capacitor). The remarkable magnetoelectric (ME) tunability comes from the additional and voltage-induced ferromagnetic ordering, caused by uncompensated d-orbital electrons in the Pt metal layer. Confirmed by first-principle calculations, this finding paves the way for novel voltage-tunable YIG-based spintronics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Electric field (E-field) modulation of perpendicular magnetic anisotropy (PMA) switching, in an energy-efficient manner, is of great potential to realize magnetoelectric (ME) memories and other ME devices. Voltage control of the spin-reorientation transition (SRT) that allows the magnetic moment rotating between the out-of-plane and the in-plane direction is thereby crucial. In this work, a remarkable magnetic anisotropy field change up to 1572 Oe is achieved under a small operation voltage of 4 V through ionic liquid (IL) gating control of SRT in Au/[DEME] + [TFSI] - /Pt/(Co/Pt) 2 /Ta capacitor heterostructures at room temperature, corresponding to a large ME coefficient of 378 Oe V -1 . As revealed by both ferromagnetic resonance measurements and magnetic domain evolution observation, the magnetization can be switched stably and reversibly between the out-of-plane and in-plane directions via IL gating. The key mechanism, revealed by the first-principles calculation, is that the IL gating process influences the interfacial spin-orbital coupling as well as net Rashba magnetic field between the Co and Pt layers, resulting in the modulation of the SRT and in-plane/out-of-plane magnetization switching. This work demonstrates a unique IL-gated PMA with large ME tunability and paves a way toward IL gating spintronic/electronic devices such as voltage tunable PMA memories., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Ionic-liquid gating on a functional thin film with a low voltage has drawn a lot of attention due to rich chemical, electronic, and magnetic phenomena at the interface. Here, a key challenge in quantitative determination of voltage-controlled magnetic anisotropy (VCMA) in Au/[DEME] + [TFSI] - /Co field-effect transistor heterostructures is addressed. The magnetic anisotropy change as response to the gating voltage is precisely detected by in situ electron spin resonance measurements. A reversible change of magnetic anisotropy up to 219 Oe is achieved with a low gating voltage of 1.5 V at room temperature, corresponding to a record high VCMA coefficient of ≈146 Oe V -1 . Two gating effects, the electrostatic doping and electrochemical reaction, are distinguished at various gating voltage regions, as confirmed by X-ray photoelectron spectroscopy and atomic force microscopy experiments. This work shows a unique ionic-liquid-gating system for strong interfacial magnetoelectric coupling with many practical advantages, paving the way toward ion-liquid-gating spintronic/electronic devices., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)