Nanoscale spin crossover materials capable of undergoing reversible switching between two electronic configurations with markedly different physical properties are excellent candidates for various ...technological applications. In particular, they can serve as active materials for storing and processing information in photonic, mechanical, electronic, and spintronic devices as well as for transducing different forms of energy in sensors and actuators. In this progress report, a brief overview on the current state‐of‐the‐art of experimental and theoretical studies of nanomaterials displaying spin transition is presented. Based on these results, a detailed analysis and discussions in terms of finite size effects and other phenomena inherent to the reduced size scale are provided. Finally, recent research devices using spin crossover complexes are highlighted, emphasizing both challenges and prospects.
Spin crossover nanomaterials can serve as active elements for processing information and for transducing different forms of energy in sensors and actuators. The different physical mechanisms governing the spin transition at the nanoscale are summarized and the concept of spin‐state dependent surface energy is highlighted. Finally, photonic, electronic, and mechanical devices using spin crossover complexes are reviewed.
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Fundamental aspects of spin crossover (SCO) mechanisms are reviewed through considerations of ligand/crystal field theory, thermodynamics, and modeling of the thermoinduced spin transition in the ...solid state based on macroscopic–mesoscopic approaches . In particular, we highlight success of thermodynamic models in the simulation of first-order spin transitions with hysteretic behaviors (bistability) and multistep conversions. Bistability properties originate from elastic interactions, the so-called cooperativity between SCO molecules in the crystal packing. Although physical and chemical properties and thermodynamical quantities of noninteracting SCO compounds can be readily injected in macroscopic models, taking cooperativity into account remains problematic. The relationship between phenomenological numerical parameters and experimentally accessible quantities can only be most of the time indirectly established. Recent extensions of these thermodynamical models to grasp SCO properties at the nanoscale and combinations with ab initio numerical methods show that macroscopic models still constitute useful theoretical tools to investigate SCO phenomena. The necessity to further probe the thermomechanical properties of SCO materials is also emphasized.
Dans cette revue, les aspects fondamentaux des mécanismes de conversion de spin sont abordés au travers de divers formalismes théoriques bien connus en physique et chimie de la matière condensée, tels que la théorie du champ de ligand/cristallin, la thermodynamique des mélanges binaires et les modèles macroscopiques–mesoscopiques associés pour simuler la transition de spin thermo-induite. En particulier, nous rapportons les différents succès des modèles thermodynamiques dans la simulation de transitions de spin du premier ordre présentant des phénomènes d'hystérésis (bistabilité) et des transitions en plusieurs étapes. L'existence du phénomène de bistabilité est directement reliée aux mécanismes d'interaction élastique entre les molécules à conversion de spin appelés « cooperativité ». Alors que les propriétés physiques et chimiques ainsi que les quantités thermodynamiques des composés à conversion de spin isolés peuvent être facilement injectées dans des modèles macroscopiques, la prise en compte de la coopérativité reste compliquée à réaliser. La relation entre les paramètres numériques phénoménologiques et les quantités accessibles expérimentalement ne peut être, la plupart du temps, établie que de manière indirecte. Des extensions récentes de ces modèles thermodynamiques destinées à mieux comprendre les propriétés de la conversion de spin à l'échelle nanométrique combinées à des méthodes numériques ab initio montrent que les modèles thermodynamiques constituent toujours un outil théorique utile pour étudier la transition de spin. La nécessité d’étudier davantage les propriétés statiques et de transport thermomécaniques de cette classe de matériaux bistables est également soulignée.
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Recently we assisted a strong renewed interest in the fascinating field of molecular spin crossover complexes by (1) the emergence of nanosized spin crossover materials through direct synthesis of ...coordination nanoparticles and nanopatterned thin films as well as by (2) the use of novel sophisticated high spatial and temporal resolution experimental techniques and theoretical approaches for the study of spatiotemporal phenomena in cooperative spin crossover systems. Besides generating new fundamental knowledge on size-reduction effects and the dynamics of the spin crossover phenomenon, this research aims also at the development of practical applications such as sensor, display, information storage and nanophotonic devices. In this critical review, we discuss recent work in the field of molecule-based spin crossover materials with a special focus on these emerging issues, including chemical synthesis, physical properties and theoretical aspects as well (223 references).
Abstract
Temperature measurement at the nanoscale is of paramount importance in the fields of nanoscience and nanotechnology, and calls for the development of versatile, high-resolution thermometry ...techniques. Here, the working principle and quantitative performance of a cost-effective nanothermometer are experimentally demonstrated, using a molecular spin-crossover thin film as a surface temperature sensor, probed optically. We evidence highly reliable thermometric performance (diffraction-limited sub-µm spatial, µs temporal and 1 °C thermal resolution), which stems to a large extent from the unprecedented quality of the vacuum-deposited thin films of the molecular complex Fe(HB(1,2,4-triazol-1-yl)
3
)
2
used in this work, in terms of fabrication and switching endurance (>10
7
thermal cycles in ambient air). As such, our results not only afford for a fully-fledged nanothermometry method, but set also a forthcoming stage in spin-crossover research, which has awaited, since the visionary ideas of Olivier Kahn in the 90’s, a real-world, technological application.
•The article reviews spin crossover polymer composite materials.•Recent development in spin crossover polymers.•Elaboration of soft materials based on spin crossover compounds.
We review the ...synthesis, properties and applications of spin crossover polymer composites, polymers and some related ‘soft’ materials. These materials have received recently much attention because they provide an efficient way for the processing of spin crossover complexes in various shapes at various size scales and can give rise also to unique physical properties. First, we discuss in detail the state of the art of the elaboration of spin crossover polymer composites, using either inorganic complex precursors in solution or preformed spin crossover powder. A particular attention is paid on the influence of the polymer matrix on the spin crossover properties and on the use of ‘active’ polymers for development of synergies between the properties of the matrix and the load. Polymer composite devices for applications in the fields of artificial muscles, energy harvesting and thermochromic sensors are also highlighted. Then, more recent works, in which organic polymeric chains are used as ligands for the transition metal ions are presented. Finally, we overview various related ‘soft’ spin crossover compounds including spin crossover dendrimers, gels, liquid crystals and Langmuir Blodgett films with particular emphasis on compounds with supramolecular interactions of alkyl chains.
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•The interest of molecule-based switches for MEMS/NEMS applications is highlighted.•An overview of current smart actuator materials is provided.•Actuating examples of different families of molecular ...switches are discussed.•Prospects and challenges are analyzed.
Molecular switches rely on various physico-chemical phenomena, and in most cases the switching event is accompanied by a significant rearrangement of atomic positions. At the macroscopic level the long range order of switching molecules usually results in a collective, or even cooperative, volume change, which can be readily exploited for actuating purposes. These molecular (or molecule-based) systems can provide multiple advantages for this type of application due, primarily, to their intrinsic chemical and functional versatility and the small size of their functional units. This review provides an overview of advances and presents the prospects for integrating switchable molecular materials as active elements into actuator devices, with particular emphasis on micro- and nanoscale systems.
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Spin crossover particles of formula Fe{(Htrz)2(trz)}0.9(NH2‐trz)0.3(BF4)1.1 and average size of 20 nm ± 8 nm are homogeneously dispersed in poly(vinylidene fluoride‐co‐trifluoro‐ethylene), ...P(VDF‐TrFE), and poly(vinylidene fluoride) (PVDF) matrices to form macroscopic (cm‐scale), freestanding, and flexible nanocomposite materials. The composites exhibit concomitant thermal expansion and discharge current peaks on cycling around the spin transition temperatures, i.e., new “product properties” resulting from the synergy between the particles and the matrix. Poling the P(VDF‐TrFE) (70–30 mol%) samples loaded with 25 wt% of particles in 18 MV m−1 electric field results in a piezoelectric coefficient d33 = −3.3 pC N−1. The poled samples display substantially amplified discharges and altered spin transition properties. Analysis of mechanical and dielectric properties reveals that both strain (1%) and permittivity (40%) changes in the composite accompany the spin transition in the particles, giving direct evidence for strong electromechanical couplings between the components. These results provide a novel route for the deployment of molecular spin crossover materials as actuators in artificial muscles and generators in thermal energy harvesting devices.
P(VDFTrFE) and poly(vinylidene fluoride) (PVDF) composites of spin transition nanoparticles are synthesized to obtain flexible, freestanding, macroscopic objects displaying original electromechanical properties. The synergy between the components leads to concomitant thermal expansion and electrical discharge peaks at the spin transition providing scope for the deployment of spin crossover materials as actuators in artificial muscles and generators in thermal‐energy‐harvesting devices.
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The lattice dynamical aspects of the spin crossover phenomenon in molecular solids—displaying intricate couplings between the electronic spin state of the molecules and the lattice properties—are ...reviewed. Emphasis is on experimental and theoretical approaches giving access to the vibrational spectra and to key properties, such as the heat capacity, vibrational entropy and enthalpy, lattice rigidity, elastic constants, and elastic interactions. Recent results in relation to surface and finite size effects as well as with ultrafast out‐of‐equilibrium phenomena are also covered.
The interplay between the molecular spin state switching and associated variation of lattice dynamical properties are reviewed with particular attention on the vibrational thermodynamics and elastic properties. Emerging topics, including size reduction effects and ultrafast dynamics are also discussed.
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9.
Spin Crossover at the Nanometre Scale Shepherd, Helena J.; Molnár, Gábor; Nicolazzi, William ...
European journal of inorganic chemistry,
February 2013, Volume:
2013, Issue:
5-6
Journal Article
Peer reviewed
Open access
From the development of new methods for the synthesis and patterning of nanometre‐scale thin films and particles, to the first investigations of charge transport and photonic properties, there has ...been a proliferation of research concerning spin crossover nanomaterials in recent years. Studies have aimed at addressing fundamental questions concerning size‐reduction effects, as well as striving towards practical applications in this important class of bistable molecular materials. This microreview describes the most recent achievements and highlights possible future directions in this field.
Recent investigations of spin crossover nanomaterials reveal not only interesting size‐reduction effects on their equilibrium and dynamical properties, but also highlight exciting perspectives for the development of nanophotonic and nanoelectronic devices.
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