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Funding Information: This work was supported by the Academy of Finland (Grant Nos. 316857 and 295269). The authors wish to acknowledge CSC – IT Center for Science, Finland, and the Aalto Science‐IT project for computational resources. Publisher Copyright: © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH. The voltage control of magnetism is a promising path to the development of low-power spintronic devices. Magneto-ionics—exploiting voltage-driven ion migration to control magnetism—has attracted interest because it can generate large magnetoelectric effects at low voltage. Here, the use of the solid-state lithium-ion battery technology for reversible voltage-controlled switching between perpendicular and in-plane magnetization states in a Co–Pt bilayer is demonstrated. Due to the small size and high mobility of lithium ions, small voltages produce an exceptionally high magnetoelectric coupling efficiency of at least 7700 fJ V–1 m–1 at room temperature. The magnetic switching effect is attributed to the modulation of spin-orbit coupling at the Co–Pt interface when lithium ions migrate between a lithium storage layer (LiCoO2) and the magnetic interface across a lithium phosphorous oxynitride (LiPON) solid-state electrolyte, which is corroborated by density functional theory calculations. Voltage control of magnetism in the battery structure does not show degradation over more than 500 voltage cycles, demonstrating promise for solid-state lithium-based magneto-ionic devices.

Deterministic polarization reversal in ferroelectric and multiferroic films is critical for their exploitation in nanoelectronic devices. While ferroelectricity has been studied for nearly a century, major discrepancies in the reported values of coercive fields and saturation polarization persist in literature for many materials. This raises questions about the atomic‐scale mechanisms behind polarization reversal. Unconventional ferroelectric switching in ε‐Fe2O3 films, a material that combines ferrimagnetism and ferroelectricity at room temperature, is reported. High‐resolution in situ scanning transmission electron microscopy experiments and first‐principles calculations demonstrate that polarization reversal in ε‐Fe2O3 occurs around pre‐existing domain walls only, triggering local domain wall motion in moderate electric fields of 250–500 kV cm−1. Calculations indicate that the activation barrier for switching at domain walls is nearly a quarter of that corresponding to the most likely transition paths inside ε‐Fe2O3 domains. Moreover, domain walls provide symmetry lowering of the polar structure near the domain boundary, which is shown to be necessary for ferroelectric switching in ε‐Fe2O3. Local polarization reversal in ε‐Fe2O3 limits the macroscopic ferroelectric response and offers important hints on how to tailor ferroelectric properties by domain structure design in other relevant ferroelectric materials., This work was supported by the Academy of Finland (Grant Nos. 293929, 304291, 319218 and 316857) and by the European Research Council (ERC‐2012‐StG 307502 and ERC‐2018‐CoG 819623). STEM analysis was conducted at the Aalto University OtaNano‐Nanomicroscopy Center (Aalto‐NMC). ICMAB acknowledges financial support from the Spanish Ministry of Economy, Competitiveness and Universities, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV‐ 2015‐0496) and the project MAT2017‐85232‐R co‐financed with the EU FEDER program, as well as the Generalitat de Catalunya (projects 2017SGR1377 and 2017SGR765). The authors thank Jaume Gàzquez for discussions about the work and critical reading of the manuscript. K.Z.R. and M.L. gratefully acknowledge the financial support by Deutsche Forschungsgemeinschaft (DFG) through DFG‐ANR GALIMEO project (LE 2504/2‐1), as well as the support of Jülich Supercomputing Centre (JSC, project jiff38) and JARA‐HPC Partition (projects jara0081 and jara0126). R.C.Y. and X.X.G. acknowledge the financial support by the National Key Research Program of China (Grant No. 2017YFA0206200) and the National Natural Science Foundation of China (Grant No. 11874413). We thank Prof. Nathalie Viart for valuable discussions.

A critical factor for electronics based on inorganic layered crystals stems from the electrical contact mode between the semiconducting crystals and the metal counterparts in the electric circuit. Here, a materials tailoring strategy via nanocomposite decoration is carried out to reach metallic contact between MoS2 matrix and transition metal nanoparticles. Nickel nanoparticles (NiNPs) are successfully joined to the sides of a layered MoS2 crystal through gold nanobuffers, forming semiconducting and magnetic NiNPs@MoS2 complexes. The intrinsic semiconducting property of MoS2 remains unchanged, and it can be lowered to only few layers. Chemical bonding of the Ni to the MoS2 host is verified by synchrotron radiation based photoemission electron microscopy, and further proved by first- principles calculations. Following the system's band alignment, new electron migration channels between metal and the semiconducting side contribute to the metallic contact mechanism, while semiconductor–metal heterojunctions enhance the photocatalytic ability.

Magnetoplasmonics is an emerging field of intense research on materials combining magnetic and plasmonic functionalities. The novel optical and magneto-optical (MO) properties displayed by these materials could allow the design of a new class of magnetically controllable optical nano-devices. In this work, we investigate the effects of a non-absorbing (insulating) substrate on the MO activity of pure ferromagnetic disk-shaped nanostructures supporting localized plasmon resonances. We show that the red-shift of the localized plasmon resonance, related to the modification of the localization of the electromagnetic field due to the substrate, is not the only effect that the substrate has on the MO response. We demonstrate that the reflectivity of the substrate itself plays a key role in determining the MO response of the system. We discuss why it is so and provide a description of the modeling tools suitable to take into account both effects. Understanding the role of the substrate will permit a more aware design of magnetoplasmonic nanostructured devices for future biotechnological and optoelectronic applications. Ferromagnetic nickel nanodisk in vacuum (left) and on a non-absorbing substrate (right), illuminated by linearly polarized light. The polarization of the reflected field is changed in the first case due to a combination of intrinsic magneto-optical properties and the nanoconfinement of the material. In the second case, the polarization of the reflected light is affected also by the presence of the substrate. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Energy efficiency, parallel information processing, and unsupervised learning make the human brain a model computing system for unstructured data handling. Different types of oxide memristors can emulate synaptic functions in artificial neuromorphic circuits. However, their cycle-to-cycle variability or strict epitaxy requirements remain a challenge for applications in large-scale neural networks. Here, solution-processable ferroelectric tunnel junctions (FTJs) with P(VDF-TrFE) copolymer barriers are reported showing analog memristive behavior with a broad range of accessible conductance states and low energy dissipation of 100 fJ for the onset of depression and 1 pJ for the onset of potentiation by resetting small tunneling currents on nanosecond timescales. Key synaptic functions like programmable synaptic weight, long- and short-term potentiation and depression, paired-pulse facilitation and depression, and Hebbian and anti-Hebbian learning through spike shape and timing-dependent plasticity are demonstrated. In combination with good switching endurance and reproducibility, these results offer a promising outlook on the use of organic FTJ memristors as building blocks in artificial neural networks.

The possibility to tailor ferroelectricity by controlling epitaxial strain in thin films and heterostructures of complex metal oxides is well established. Here it is demonstrated that apart from this mechanism, 3D film growth during heteroepitaxy can be used to favor specific domain configurations that lead to step-like polarization switching and a giant nonlinear dielectric response in sub-switching ac electric fields. A combination of cube-on-cube epitaxial growth and the formation of columnar structures during pulsed laser deposition of Pb0.5Sr0.5TiO3 films on La0.5Sr0.5CoO3 bottom electrode layers and MgO (001) substrates stabilizes ferroelectric nanodomains with enhanced dynamic properties. In the Pb0.5Sr0.5TiO3 films, a- and c-oriented epitaxial columns grow from the bottom to the top of the film leading to random polydomain architectures with strong associations between the ferroelectric domains and the nanocolumns. Polarization switching in the two domain populations is initiated at distinctive fields due to domain wall pinning on column boundaries. Moreover, piezoelectric coupling between ferroelectric domains leads to strong interdomain elastic interactions, which result in an enhanced Rayleigh-type dielectric nonlinearity. The growth of epitaxial films with 3D columnar structures opens up new routes towards the engineering of enhanced ferroelectric and electromechanical functions in a broad class of complex oxide materials.

A detailed study of the magnetization reversal process in [20 A Pt/t A Co] 3 /100 A IrMn/20 A Pt multilayers with 4 A ≤ t ≤ 9 A is presented. The hysteresis of as-deposited films with t ≥ 5 A is found to be asymmetric. This asymmetry is explained by a lateral variation in the perpendicular exchange bias direction due to the growth of IrMn onto multi-domain Co/Pt multilayers.