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Abstract The fabrication and development of high-entropy alloys (HEAs) with exceptional functionalities is a rapidly expanding field with numerous applications. When the role of entropy in HEAs is considered, the extrinsic factors, such as the existence of grains and different phases, need to be separated from the intrinsic configurations of the atomic lattice. Here, we fabricated the CoCrFeNi2Al0.5 HEA/muscovite heterostructures, and some were prepared as epitaxial bilayers and others were prepared as an amorphous system. These two systems are classified into atomic-site disordered (ASD) and structurally disordered (SD) states, respectively, without the extrinsic effects for the determination of the crystal lattice role in high-entropy states. In this study, we determined the role of the structure order in correlation with the structural, electronic, and magnetic properties of HEAs using a combination of energy-dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, magneto-transport, ac magnetometry, and X-ray absorption spectroscopy with magnetic circular dichroism. The ASD state showed fully metallic behavior. In contrast, the SD state showed a metallic behavior with intense magnetic saturation, which was called Kondo-like behavior, under 50 K with a low-temperature coefficient of resistivity of ~64 ppm/°C. The difference between the saturation magnetic moment and the electron relaxation behavior in the ASD and SD states resulted from the existence of the structural order affecting the atomic distance and periodicity to modify the exchange interaction and tune the electron-phonon interaction for scattering. The ferromagnetic behavior contributed by Co, Fe, and Ni atoms was probed by X-ray absorption and magnetic circular dichroism to understand the magnetic interactions in the ASD and SD states.

The advancement of flexible technology, such as wearable devices, foldable mobile, and automobiles, has entered a new era. Recently, MICAtronics using flexible muscovite carriers has been introduced as a novel area for flexible technology. The muscovite substrate addresses challenges such as thermal budget and chemical stability, offering outstanding environmental stability and an alternative approach to the prevalent polymer-based soft technology. However, the role of muscovite in these studies has been limited to serving as substrates. We expand the scope of muscovite applications by proposing a new form called “intercalated muscovite.” In this study, we insert transition metal ions, creating a novel layout of muscovite substrates. Subsequent heat treatment and controlled atmospheres can generate various forms of inserted species. These intercalated systems reveal new physical properties of muscovite substrates, offering a fresh avenue for MICAtronics.

Abstract In modern technology, recent advances in multi-functional devices are rapidly developed for the diverse demands of human beings. Meanwhile, durability and adaptability to extreme environmental conditions are also required. In this study, a flexible magnetoelectric (ME) heterostructure based on CoFe2O4/Pb(Zr,Ti)O3 composite thin film on muscovite is presented, with two geometries of the constituents, namely laminar heterostructure, and vertical nanostructure, adopted for the comparison. On the other hand, credited to the mechanical flexibility of muscovite, the impact of flexibility on ME properties is also discussed with a series of bending tests. Moreover, the ME response sustains for 10,000 times bending without significant decrease, validating the mechanical durability of this heterostructure on muscovite. With these advantages, a flexible proximity sensor based on this heterostructure is demonstrated for motion detection. It is expected to offer a pathway for creating the next-generational flexible devices, showing potential for future practical application.

Self-assembled nanocomposites present opportunities for a range of phase morphologies and desirable properties. Here authors present tuneable self-assembled nanostructures in the SnO2:NiO system; the double-percolated system expands the design of self-assembled oxides for practical applications, e.g. in optoelectronics.

Despite various known topological polar structures, the dynamic property of isolated ones is still poorly understood. Here, the authors show the controlled nucleation and ability to move of isolated three-fold vertices under an applied electric field.

A versatile top-down strategy has been shown to produce amorphous oxides through amorphization of corresponding hydroxides. This approach was used to generate various unitary, binary and ternary amorphous oxides for electrocatalytic oxygen evolution.

Abstract Recent advances in the design and development of magnetic storage devices have led to an enormous interest in materials with perpendicular magnetic anisotropy (PMA) property. The past decade has witnessed a huge growth in the development of flexible devices such as displays, circuit boards, batteries, memories, etc. since they have gradually made an impact on people’s lives. Thus, the integration of PMA materials with flexible substrates can benefit the development of flexible magnetic devices. In this study, we developed a heteroepitaxy of BaFe12O19 (BaM)/muscovite which displays both mechanical flexibility and PMA property. The particular PMA property was characterized by vibrating sample magnetometer, magnetic force microscopy, and x-ray absorption spectroscopy. To quantify the PMA property of the system, the intrinsic magnetic anisotropy energy density of ~2.83 Merg cm−3 was obtained. Furthermore, the heterostructure exhibits robust PMA property against severe mechanical bending. The findings of this study on the BaM/muscovite heteroepitaxy have several important implications for research in next-generation flexible magnetic recording devices and actuators.

Abstract In condensed matter physics, oxide materials show various intriguing physical properties. Therefore, many efforts are made in this field to develop functional oxides. Due to the excellent potential for tin‐based perovskite oxides, an expansion of new related functional compounds is crucial. This work uses a heteroepitaxial approach supported by theoretical calculation to stabilize PbSnO3 thin films with different orientations. The analyses of X‐ray diffraction and transmission electron microscopy unveil the structural information. A typical antiferroelectric feature with double hysteresis and butterfly loops is observed through electrical characterizations consistent with the theoretical prediction. The phase transition is monitored, and the transition temperatures are determined based on temperature‐dependent structural and electrical characterizations. Furthermore, the microscopic antiferroelectric order is noticed under atomic resolution images via scanning transmission electron microscopy. This work offers a breakthrough in synthesizing epitaxial PbSnO3 thin films and comprehensively understanding its anisotropic antiferroelectric behavior.

BiFeO3 has a wide application but the impact of rare-earth substitution for the evolution of the coupling mechanism is unknown. Here, the authors reveal the correlation between ferroelectricity, antiferromagnetism, a weak ferromagnetic moment, and their switching pathways in La-substituted BiFeO3.

Advanced heterostructures composed of various materials can induce new physical properties and phenomena among existing materials, representing the essential foundation for modern electronics. Recently, many works have been carried out with novel heterostructures combining three-dimensional (3D) and two-dimensional (2D) materials; however, there is a lack of promising methods to fabricate 3D/2D heterostructures due to the poor interfacial quality and the incompatibility of fabrication processes. To further study the interaction between 3D and 2D materials, the fabrication of 3D/2D heterostructures with high-quality interfaces should be attempted. Here, we show the possibility of fabricating high-quality oxide remote epitaxies through layered materials for the exploration on new functionalities. Brand new heterostructures including numerous 3D oxides and MoS2 have been demonstrated and investigated. Our study clarifies a remarkable concept to realize precisely controllable 3D/2D/3D heteroepitaxies for the design and development of next-generation smart devices.

Abstract The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality.

To fully exploit the potential of multiferroic materials the control of their intrinsic degrees of freedom is a prerequisite. Here, the control of spin orientation in strained BiFeO3 films is demonstrated elucidating the microscopic mechanism of the complex interplay of polar and magnetic order.

Bringing together p- and n-type monolayers of semiconducting transition metal dichalcogenides results in the formation of atomically thin pn junctions. Here, the authors laterally manipulate carrier density to create a WSe2 pn homojunction on a supporting ferroelectric BiFeO3 substrate.

Two-dimensional electron gases that form in some complex oxide heterostructures may have useful functional behavior due to the interaction of the parent materials. Here the authors show that PZT/STO interfaces can host a spin-polarized electron gas, even though the bulk materials are nonmagnetic.

Understanding the conductivity at the nominally uncharged domain walls in ferroelectrics is still far from complete. Here the authors report an enhanced conduction at domain walls in an ultra-thin (001) BiFeO3 film resulting from the formation of a field-induced meta-stable twisted domain nucleus.

Ferroelectrics: Electrically rewritable vortex pairs in bismuth ferrite A demonstration of electrically-rewritable vortex pairs in a ferroelectric could provide a route to realizing vortex memory devices. Swirling vortex structures of electrical polarization that are relatively insensitive to external disturbances can form in ferroelectric materials. As they can exist in different polarization states, vortices could be exploited for information storage applications, but practical methods to manufacture and manipulate them are required first. Using scanning probe microscopy-based methods, an international team of researchers led by Xiaomei Lu from Nanjing University demonstrate that ferroelectric vortex-antivortex pairs can be created and erased in bismuth ferrite films using local electric fields. They also show that large-scale vortex networks can be created, which could bring the use of vortices in electronic devices a step closer.

Understanding ferroelectricity at reduced dimensions will be important for future sub-nanoscale devices based on ferroelectrics. Using high resolution electron microscopy; Gaoet al., observe the existence of a measurable polarization at a thickness of just 1.5-unit cells

Light-induced deformation known as photostriction could be used for green energy devices but in most materials the effect is too small to be of practical use. Here, Weiet al. study the photostriction of strontium ruthenate and find photon-induced strain efficiencies of more than one percent.

Ferroelectric reliability must be solved prior to practical non-volatile electronic devices based on magnetoelectric multiferroics. Here, Hsiehet al. report a long lasting ferroelectric retention in the heteroepitaxially constrained multiferroic mesocrystal.

Miniature of electronic devices is attractive yet challenging due to structural variation at nanoscale. Here, Gao et al. report atomic imaging of reconstruction and unusual domain walls on Pb(Zr0.2Ti0.8)O3surfaces, providing possibilities to engineer nanoscale structural change.

We utilized transmission-type pump–probe technique to investigate coherent acoustic phonons in the superlattices of perovskite oxides such as SrIrO _3 /SrTiO _3 and SrRuO _3 /SrTiO _3 . Because the films in the superlattices are of high-quality and their thicknesses are only several monolayers, quasi-monochromatic acoustic phonons with THz frequency have been achieved. By investigating the propagation of coherent acoustic phonons in the superlattices with different epitaxial periods, the phonon mean free paths of SrTiO _3 were studied in the frequency range between 0.5 THz and 1 THz. We further demonstrated coherent control to amplify or cease the THz coherent acoustic phonon oscillations in the superlattices. By controlling the delay of two pulses for shining the superlattices, the amplitude and phase of the THz coherent acoustic phonons were manipulated. According to the measurements of time-domain Brillouin scatterings, we found the optoacoustic conversion efficiency of SrIrO _3 outperforms that of SrRuO _3 for generating acoustic phonons.

Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagnetic-paramagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system toward the increase of the magnetic moment by two-times in magnitude. The magnetic moment increases with the He-ion irradiation fluence up to 2.5 × 1016/cm2. Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data, which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin-films.

The rich phase diagram of rhombohedral (R)-like and tetragonal (T)-like monoclinic polymorph in strained BiFeO3 (BFO) films brings on various functionalities. Finding correlations of physical ordering parameters in this system is generally difficult because T-like and R-like phases are undistinguishable in many aspects. In this study, the magnetic-coupled structural transitions of the mixed-phase BFO at low temperatures were investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. To resolve the complexity resulted from the similarity between T-like and R-like phases, we analyzed the Raman spectra on a micro-scale region with various T/R ratios, which is in situ manipulated by an AFM tip carrying a dc bias. Phonons of T-like and R-like phases were thus successfully separated. Based on temperature-dependent XRD and resolved Raman spectra, we observed two isostructural transitions at around 225 K and 150 K, and they are strongly correlated with the magnetic ordering in the mixed-phase BFO film. Moreover, through the effective spin-lattice coupling, the evolution of the T/R polymorph is changed by the magnetic cooling process at low temperatures. This study provides a pathway to modulate phonon behaviors by magnetic fields in a highly strained system.

Nanotopological cues can be exploited to understand the nature of interactions between cells and their microenvironment to generate superior implant geometries. Nanosurface parameters which modulate the cell behavior and characteristics such as focal adhesions, cell morphology are not clearly understood. Here, we studied the role of different nanotopographic dimensions in modulating the cell behavior, characteristics and ultimately the cell fate and accordingly, a methodology to improve implant surface geometry is proposed. Tantalum oxide nanodots of 50, 100nm dot diameter with an inter-dot spacing of 20, 70nm and heights 40, 100nm respectively, were engineered on Silicon substrates. MG63 cells were cultured for 72 hours and the modulation in morphology, focal adhesions, cell extensible area, cell viability, transcription factors and genes responsible for bone protein secretion as a function of the nanodot diameter, inter-dot distance and nanodot height were evaluated. Nanodots of 50nm diameter with a 20nm inter-dot spacing and 40nm height enhanced cell spreading area by 40%, promoted cell viability by 70% and upregulated transcription factors and genes twice as much, as compared to the 100nm nanodots with 70nm inter-dot spacing and 100nm height. Favorable interactions between cells and all dimensions of 50nm nanodot diameter were observed, determined with Scanning electron microscopy and Immunofluorescence staining. Nanodot height played a vital role in controlling the cell fate. Dimensions of nanodot features which triggered a transition in cell characteristics or behavior was also defined through statistical analysis. The findings of this study provide insights in the parameters of nanotopographic features which can vitally control the cell fate and should therefore be taken into account when designing implant geometries.