The field of spin‐crossover complexes is rapidly evolving from the study of the spin transition phenomenon to its exploitation in molecular electronics. Such spin transition is gradual in a single‐molecule, while in bulk it can be abrupt, showing sometimes thermal hysteresis and thus a memory effect. A convenient way to keep this bistability while reducing the size of the spin‐crossover material is to process it as nanoparticles (NPs). Here, the most recent advances in the chemical design of these NPs and their integration into electronic devices, paying particular attention to optimizing the switching ratio are reviewed. Then, integrating spin‐crossover NPs over 2D materials is focused to improve the endurance, performance, and detection of the spin state in these hybrid devices.

A simple chemical protocol to prepare core–shell gold@spin‐crossover (Au@SCO) nanoparticles (NPs) based on the 1D spin‐crossover [Fe(Htrz)₂(trz)](BF₄) coordination polymer is reported. The synthesis relies on a two‐step approach consisting of a partial surface ligand substitution of the citrate‐stabilized Au NPs followed by the controlled growth of a very thin layer of the SCO polymer. As a result, colloidally stable core@shell spherical NPs with a Au core of ca. 12 nm and a thin SCO shell 4 nm thick, are obtained, exhibiting a narrow distribution in sizes. Differential scanning calorimetry proves that a cooperative spin transition in the range 340–360 K is maintained in these Au@SCO NPs, in full agreement with the values reported for pristine 4 nm SCO NPs. Temperature‐dependent charge‐transport measurements of an electrical device based on assemblies of these Au@SCO NPs also support this spin transition. Thus, a large change in conductance upon spin state switching, as compared with other memory devices based on the pristine SCO NPs, is detected. This results in a large improvement in the sensitivity of the device to the spin transition, with values for the ON/OFF ratio which are an order of magnitude better than the best ones obtained in previous SCO devices.

Robust hybrid [Fe(Htrz) ₂ (trz)](BF ₄ )@SiO ₂ nanoparticles with reduced sizes (from ca . 90 to 28 nm) and ultrathin silica shells (<3 nm) have been obtained, presenting abrupt spin transition and reduced thermal hysteresis.

In the past years, the use of highly sensitive Silicon Micro-Electro-Mechanical cantilevers has been proposed as a tool to characterize the spin-crossover phenomenon by employing fast optical read-out of the motion. In the present work, FeII-based spin-crossover nanoparticles of the well-known [Fe(Htrz)2(trz)](BF4) complex wrapped with a thin silica shell of different sizes will be studied by means of silicon micro-resonators. The silica shell will enhance its chemical stability, while the low thickness allows a proper mechanical coupling between the cantilever and the spin-crossover core. To maximize the sensing of the spin-crossover phenomena different cantilever geometries and flexural modes were employed. In addition, the experimental observation was also compared by COMSOL numerical simulations, which are in close agreement with them. The probe of spin-crossover phenomena with micro and nanoelectro mechanical actuators offers the possibility to prepare smart sensing memory devices near/above room temperature.