Mixed-halide lead perovskite (MHP) materials are rapidly advancing as next-generation high-efficiency perovskite solar cells due to enhanced stability and bandgap tunability. In this work, we demonstrate the ability to readily and stoichiometrically tune the halide composition in methylammoniumbased MHPs using a mechanochemical synthesis approach. Using this solvent-free protocol we are able to prepare domain-free MHP solid solutions with randomly distributed halide ions about the Pb center. Up to seven distinct [PbCl x Br 6−x ] 4− environments are identified, based on the 207 Pb NMR chemical shifts, which are also sensitive to the changes in the unit cell dimensions resulting from the substitution of Br by Cl, obeying Vegard's law. We demonstrate a straightforward and rapid synthetic approach to forming highly tunable stoichiometric MHP solid solutions while avoiding the traditional solution synthesis method by redirecting the thermodynamically driven compositions. Moreover, we illustrate the importance of complementary characterization methods, obtaining atomic-scale structural information from multinuclear, multifield, and multidimensional solid-state magnetic resonance spectroscopy, as well as from quantum chemical calculations and long-range structural details using powder X-ray diffraction. The solvent-free mechanochemical synthesis approach is also compared to traditional solvent synthesis, revealing identical solid-solution behavior; however, the mechanochemical approach offers superior control over the stoichiometry of the final mixed-halide composition, which is essential for device engineering.

Mixed-halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium-based mixed halide perovskites (FA-MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent-free mechanochemical synthesis (MCS) method to prepare FA-MHPs, starting with their parent compounds (FAPbX; X = Cl, Br, I), achieving compositions not previously accessible through the solvent synthesis (SS) technique. By probing local Pb environments in MCS FA-MHPs using solid-state nuclear magnetic resonance spectroscopy, along with powder X-ray diffraction for long-range crystallinity and reflectance measurements to determine the optical band gap, we show that MCS FA-MHPs form atomic-level solid solutions between Cl/Br and Br/I MHPs. Our results pave the way for advanced methods in atomic-level structural understanding while offering a one-pot synthetic approach to prepare MHPs with superior control of stoichiometry.

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Memristors represent the fourth electrical circuit element complementing resistors, capacitors and inductors. Hallmarks of memristive behavior include pinched and frequency-dependent I-V hysteresis loops and most importantly a functional dependence of the magnetic flux passing through an ideal memristor on its electrical charge. Microtubules (MTs), cylindrical protein polymers composed of tubulin dimers are key components of the cytoskeleton. They have been shown to increase solution's ionic conductance and re-orient in the presence of electric fields. It has been hypothesized that MTs also possess intrinsic capacitive and inductive properties, leading to transistor-like behavior. Here, we show a theoretical basis and experimental support for the assertion that MTs under specific circumstances behave consistently with the definition of a memristor. Their biophysical properties lead to pinched hysteretic current-voltage dependence as well a classic dependence of magnetic flux on electric charge. Based on the information about the structure of MTs we provide an estimate of their memristance. We discuss its significance for biology, especially neuroscience, and potential for nanotechnology applications. MemristorsThe term memristor is the contraction of memory and resistor and it was first proposed in 1971 as the fourth element of the electric circuits 1 . A memristor is defined as a two-terminal passive circuit element that provides a functional relation between electric charge and magnetic flux 1,2 . The first physical realization of a memristor was achieved in 2008 2,3 and it has held a promise of nanoelectronics beyond Moore's law 4 , although this realization has been both difficult and controversial 5 . One of the possible breakthrough applications of memristors is neuromorphic computing 6 . Memristance refers to a property of the memristor that is analogous to resistance but it also depends on the history of applied voltage or injected current, unlike in other electrical circuit elements. When the electrical charge flows in one direction, the resistance of some memristors increases while it decreases when the charge flows in the opposite direction or vice versa. If the applied voltage is turned off, the memristor retains the last resistance value that it exhibited. This history dependence of memristance is expressed via a self-crossing or pinched I-V loop, which is frequency dependent 3,6 , and whose lobe area tends to zero as the frequency tends to infinity.A memristor is said to be charge-controlled if the relation between flux ϕ and charge q is: ϕ = ϕ (q). Conversely, it is said to be flux-controlled if q = q(ϕ). The voltage v of a charge-controlled memristor obeys a linear relationship with the current i(t) representing a charge-dependent Ohm's law such that: v(t) M(q) i(t)(1) = where memristance is defined as:

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We have measured the spin injection efficiency and spin lifetime in Co2FeSi/n-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe large (∼40 µV) spin valve signals at room temperature and injector currents of 10 3 A/cm 2 , facilitated by fabricating spin valve separations smaller than the 1 µm spin diffusion length and applying a forward bias to the detector contact. The spin transport parameters are measured by comparing the injector-detector contact separation dependence of the spin valve signal with a numerical model accounting for spin drift and diffusion. The apparent suppression of the spin injection efficiency at the lowest temperatures reflects a breakdown of the ordinary drift-diffusion model in the regime of large spin accumulation. A theoretical calculation of the D'yakonov-Perel spin lifetime agrees well with the measured n-GaAs spin lifetime over the entire temperature range. arXiv:1610.03797v1 [cond-mat.mes-hall]

The discovery of topological insulators, materials with bulk band gaps and protected cross-gap surface states in compounds such as Bi2Se3, has generated much interest in identifying topological surface states (TSSs) in other classes of materials. In particular, recent theoretical calculations suggest that TSSs may be found in half-Heusler ternary compounds. If experimentally realizable, this would provide a materials platform for entirely new heterostructure spintronic devices that make use of the structurally identical but electronically varied nature of Heusler compounds. Here we show the presence of a TSS in epitaxially grown thin films of the half-Heusler compound PtLuSb. Spin- and angle-resolved photoemission spectroscopy, complemented by theoretical calculations, reveals a surface state with linear dispersion and a helical tangential spin texture consistent with previous predictions. This experimental verification of topological behaviour is a significant step forward in establishing half-Heusler compounds as a viable material system for future spintronic devices.

Certain two-dimensional (2D) materials exhibit intriguing properties such as valley polarization 1 , ferroelectricity 2 , superconductivity 3 and charge-density waves 4,5 . Many of these materials can be manually assembled into atomic-scale multilayer devices 6,7 under ambient conditions, owing to their exceptional chemical stability. Efforts have been made to add a magnetic degree of freedom to these 2D materials via defects, but only local magnetism has been achieved 8-10 . Only with the recent discoveries of 2D materials supporting intrinsic ferromagnetism have stacked spintronic devices become realistic 11-15 . Assembling 2D multilayer devices with these ferromagnets under ambient conditions remains challenging due to their sensitivity to environmental degradation, and magnetic order at room temperature is rare in van der Waals materials. Here, we report the growth of air-stable ultra-thin epsilon-phase iron oxide crystals that exhibit magnetic order at room temperature. These crystals require no passivation and can be prepared in large quantity by cost-effective chemical vapor deposition (CVD). We find that the epsilon phase, which is energetically unfavorable and does not form in bulk, can be easily made in 2D down to a seven unit-cell thickness. Magneto-optical Kerr effect (MOKE) magnetometry of individual crystals shows that even at this ultrathin limit the epsilon phase exhibits robust magnetism with coercive fields of hundreds of mT. These measurements highlight the advantages of ultrathin iron oxide as a promising candidate towards air-stable 2D magnetism and integration into 2D spintronic devices.Iron oxides are abundant in nature and are present in almost every domain on earth, including the atmosphere, biosphere and lithosphere. 16 They are also among the most studied metal oxides, having been applied exhaustively for technological applications such as data storage and catalysis, and biomedical applications such as drug delivery, medical imaging, and cancer treatment. 16 The most common polymorphs of iron oxide are -Fe2O3 (hematitie), -Fe2O3 (maghemite), and Fe3O4 (magnetite), which exist in both bulk and nanoscale forms. In contrast, -Fe2O3 is a rare phase with little natural existence and has only been found at the nanoscale. 17 It has received far less research interest than the other polymorphs, due partially to its difficulty in preparation, as it cannot be grown in bulk. However, -Fe2O3 has a variety of interesting characteristics, such as ferrimagnetism, multiferroicity 18 , and a large coercive field 19 , motivating investigation into growth techniques and properties. Figure 1Phase identification by Raman spectroscopy. 22 out of 23 thin crystal samples measured on the same substrate are  phase. Only the thickest is −Fe 2 O 3 , suggesting that Fe2O3 preferentially forms into a stable  phase in 2D, unlike in bulk. Extended Data