Spin-crossover (SCO) materials form an intriguing class of compounds in which various external physical or chemical stimuli can change their ground spin state between a low-spin (LS) and a high-spin (HS) near room-temperature. [1][2][3][4] It has been a long standing dream to use this phenomenon in solid-state electronic devices. [5] Only recently several research groups succeeded in electrically addressing SCO materials based on Fe (II) coordination compounds at the nanoscopic [6][7][8] and microscopic [8][9][10] levels. This electric control of the spin has even been achieved in individual SCO molecules. [11,12] 2 The most investigated SCO systems are based on six-coordinated octahedral iron (II) complexes. In such systems, the spin state changes from the LS configuration, S = 0, to the HS one, S = 2; this SCO is accompanied by a change in the magnetic moment, the structure and color of the compound. Although the origin of this HS-LS transition is purely molecular, the SCO manifests cooperatively at the solid state and is strongly influenced by short/long range elastic interactions between neighboring SCO molecules. Such a cooperativity can result in a thermal hysteresis cycle, a property that can be used for memory applications in electronic devices. [5,13] In recent years the size of the SCO solid has been reduced to the nanoscale, while preserving the memory effect near room temperature. In particular, nanoparticles (NPs) of ~10 nm [14,15] have been obtained, based on the polymeric one-dimensional (1D) compound ([Fe(Htrz) 2 (trz)](BF 4 )), (Htrz = 1,2,4-triazole), [16,17] which is one of the most promising SCO systems for designing electronic devices working at room temperature. [14] SCO NPs of other materials forming 3D networks have also been studied in this context, but in most cases they undergo a fast decrease of the hysteresis width upon size reduction, which has been accompanied by a higher residual high spin fraction and a downshift of the transition temperatures. [19] Recently, the memory effect of the [Fe(Htrz) 2 (trz)](BF 4 ) NP(s) has electrically been demonstrated, [6,8,9] showing their potential as switching elements of nanoscale devices.Nevertheless, opposite behaviour in the conductivity change during the SCO transition has been reported, which remains unclear mainly due the scare experimental studies of the effects of an electric field on the charge transport properties. [20,21] In particular, measurements on single NP devices (NP mean size of 10 nm) show an increase in the electric conductivity when the SCO occurs, [6] whereas the reverse situation is observed for an assembly of NPs (mean size 15 nm) [8] and for larger particles [8][9][10] (from 100 to 300 nm in diameter and from 250 to a couple of microns in length). Although it is tempting to attribute this difference to 3 separate transport mechanisms operating in these devices, i.e, single-step tunnelling vs. multistep hopping, differences in the chemical and structural NP features as well as in the experimental conditions may not...

Future multifunctional hybrid devices might combine switchable molecules and 2D material-based devices. Spin-crossover compounds are of particular interest in this context since they exhibit bistability and memory effects at room temperature while responding to numerous external stimuli. Atomically thin 2D materials such as graphene attract a lot of attention for their fascinating electrical, optical, and mechanical properties, but also for their reliability for room-temperature operations. Here, we demonstrate that thermally induced spin-state switching of spin-crossover nanoparticle thin films can be monitored through the electrical transport properties of graphene lying underneath the films. Model calculations indicate that the charge carrier scattering mechanism in graphene is sensitive to the spin-state dependence of the relative dielectric constants of the spin-crossover nanoparticles. This graphene sensor approach can be applied to a wide class of (molecular) systems with tunable electronic polarizabilities.

We investigated the reversible electromigration in Pd-Pt nanobridges by means of in situ electron microscopy. Real-time nanometer-scale imaging with scanning transmission electron microscopy was used to determine the material transport. For high current densities (3-5 × 10(7) A cm(-2)), material transport occurs from the cathode towards the anode side, indicating a negative effective charge. The electromigration is dominated by atom diffusion at grain boundaries on the free surface. The reversal of material transport upon a change of the electric field direction could be the basis of a memristor.

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Highlights We analyzed the electromigration-induced thickness variations of thin polycrystalline films. Small camera length is required to minimize the effect of diffraction contact in STEM imaging