Charged domain walls in ferroelectrics exhibit a quasi-two-dimensional conduction path coupled to the surrounding polarization. They have been proposed for use as non-volatile memory with non-destructive operation and ultralow energy consumption. Yet the evolution of domain walls during polarization switching makes it challenging to control their location and conductance precisely, a prerequisite for controlled read-write schemes and for integration in scalable memory devices. Here, we explore and reversibly switch the polarization of square BiFeO nanoislands in a self-assembled array. Each island confines cross-shaped, charged domain walls in a centre-type domain. Electrostatic and geometric boundary conditions induce two stable domain configurations: centre-convergent and centre-divergent. We switch the polarization deterministically back and forth between these two states, which alters the domain wall conductance by three orders of magnitude, while the position of the domain wall remains static because of its confinement within the BiFeO islands.

The combination of exchange-biased systems and ferroelectric materials offers a simple and effective way to investigate the angular dependence of exchange bias using one sample with electric-field-induced competing anisotropies. A reversible electric-field-controlled magnetization reversal at zero magnetic field is also realized through optimizing the anisotropy configuration, holding promising applications for ultralow power magnetoelectric devices.

efficient and environment friendly refrigeration systems. [4] Among all the EC materials, ferroelectrics are the most promising candidate owing to their large spontaneous polarization that can be aligned by the applied electric field. The large isothermal entropy change (ΔS) induced by switching the dipoles during the polarization/depolarization process gives rise to a substantial change in the isothermal heat (Q) and adiabatic temperature (ΔT). Maximal ECE could be achieved in the vicinity of the critical Curie temperature (T c ) where the ferroelectric-paraelectric (FE-PE) phase transition induces the largest polar entropy change (ΔS). [5] For instance, by using the Maxwell relation, a giant ECE of ΔT = 12 °C was observed in Pb(Zr 0.95 Ti 0.05 ) O 3 thin films at T c of 222 °C [6] ; the same temperature change of ΔT = 12 °C was also obtained at T c of 80 °C in the organic poly(vinylidene fluoride-tri-fluoroethylene) [P(VDF-TrFE)] ferroelectric films. [7] Apparently, the T c of normal ferroelectrics are much too high to make them viable candidates for room-temperature EC cooling devices. [8] To address this issue, element doping has been adopted to transform normal ferroelectrics into relaxors in order to lower their T c to room temperature as well as to expand the narrow temperature windows of their FE-PE phase transitions, hence making them operational in a broader temperature range. [9] For instance, BaTiO 3 could be transformed from normal ferroelectrics to relaxors by doping Zr ions in B-sites. [10] As an analog to ferroelectric ceramics, ferroelectric polymers P(VDF-TrFE) can also be converted into a relaxor by copolymerization with a bulky monomer such as CFE (chlorofluoromethylene) or CTFE (chlorotrifluoroethylene). [7,11] The ternary polymers exhibit phase transitions within a large temperature span near room temperature, which is beneficial to achieving the desirable temperature windows for the ECE. Relaxor ferroelectrics also feature polar nanoregionsand lower energy barriers for dipole switching, which gives rise to large maximal electric polarizations (P s ), small remnant polarization (P r ), and low coercive electric field (E c ). [7,[12][13][14] All these features indicate that a large dipolar entropy change can be induced at a lower electric field and hence is beneficial to achieving a large EC strength that is defined as ΔT/E. [8,15] A high EC strength is much desired for EC materials to lower working voltages for The electrocaloric effect (ECE) refers to reversible thermal changes of a polarizable material upon the application or removal of electric fields. Without a compressor or cooling agents, all-solid-state electrocaloric (EC) refrigeration systems are environmentally benign, highly compact, and of very high energy efficiency. Relaxor ferroelectric ceramics and polymers are promising candidates as EC materials. Here, synergistic efforts are made by composing relaxor Ba(Zr 0.21 Ti 0.79 )O 3 nanofibers with P(VDF-TrFE-CFE) to make relaxorrelaxor-type polymer nanocomposites. The ECEs of the ...

The high demand for flexible spintronics based on multiferroic heterostructures makes growing high‐quality flexible, functional oxides urgently, in which needs to be deposited on lattice‐matched substrates. In this paper, ultraflexible and malleable iron (Fe)/BaTiO3 (BTO) multiferroic heterostructures are demonstrated, showing a perfect crystallinity and hetero‐epitaxial growth. In terms of performance, they indicate good multiferroic properties and excellent bending tunability, as well as obvious magnetoelectric (ME) coupling effect. During the phase transformation from the rhombohedral phase to the orthorhombic phase of BTO layers in the heating process, a large ME coupling coefficient of 120 Oe °C−1 along the out‐of‐plane direction is obtained. This value keeps consistent in the phase‐field simulation of magnetic domain evolution, in which the biaxial compressive strain induced‐magnetoelastic anisotropy facilitates the magnetic easy axis of Fe layers to the [110] or [–1–10] direction. Besides, ultraflexible Fe/BTO heterostructures are found to have a 690 Oe ferromagnetic resonance (FMR) field shift along the out‐of‐plane direction under the flexible tuning (R = 5 mm). This work should pave a way toward flexible spintronic and functional devices with fast speed, portability, and low energy consumption.

Quick charge/discharge polymer‐based composites filled with inorganic nanosheets have attracted extensive attention and provided a more efficient way to achieve high energy storage density (U) because of the alleviated agglomeration of fillers and the formation of conduction barriers. However, conductive paths have a chance to extend along out‐of‐plane directions by circumventing the micrometer‐sized nanosheets. Here, large‐sized (111)‐oriented BaTiO3 (BTO) films with outstanding epitaxiality and ferroelectricity are embedded in poly(vinylidene fluoride) (PVDF) using optimal transfer and hot‐pressing processes. The 2D–2D (2–2) type BTO/PVDF composites interlayered by 2‐layer BTO (about 0.2 µm thick of each layer) exhibit the highest U of 20.7 J cm‐3 at 690 MV m‐1, which is 222.6% that of pure PVDF. Phase‐field simulations reveal that high‐resistance PVDF films as outer layers can prevent the charges injection from electrodes and high‐dielectric BTO films as inner layers can effectively suppress the mobile charges across interfaces between layers, leading to a remarkable improvement of breakdown strength. This work puts forward a scalable approach to enhance the U of inorganic/organic composites for advanced energy storage materials and applications.

Reducing the switching energy of ferroelectric thin films remains an important goal in the pursuit of ultralow-power ferroelectric memory and logic devices. Here, we elucidate the fundamental role of lattice dynamics in ferroelectric switching by studying both freestanding bismuth ferrite (BiFeO3) membranes and films clamped to a substrate. We observe a distinct evolution of the ferroelectric domain pattern, from striped, 71° ferroelastic domains (spacing of ~100 nm) in clamped BiFeO3 films, to large (10’s of micrometers) 180° domains in freestanding films. By removing the constraints imposed by mechanical clamping from the substrate, we can realize a ~40% reduction of the switching voltage and a consequent ~60% improvement in the switching speed. Our findings highlight the importance of a dynamic clamping process occurring during switching, which impacts strain, ferroelectric, and ferrodistortive order parameters and plays a critical role in setting the energetics and dynamics of ferroelectric switching.

A large out-of-plane FMR shift (180 Oe/550 MHz) was observed in flexible YIG/mica thin films, which for the first time involves a flexible tunable factor f(R) in the theoretical analysis.

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