Spin-Crossover Nanoparticles in Electrospun Polymers: A Route to Bistable Materials for Smart Textiles

Developing strategies that transform crystalline molecular materials into processable forms is crucial for enabling their manipulation and integration into devices. This challenge is particularly relevant for bistable systems such as spin-crossover nanoparticles, which are often difficult to handle. Embedding these nanoparticles into organic polymers has emerged as a promising way to overcome these limitations. In this work, we investigated a series of iron-(II) triazole-based spin-crossover nanoparticles with the size of 37.0 ± 5 nm (1), 55.4 ± 9.7 nm (2), and 116.8 ± 15.5 nm (3) incorporated into electrospun PVP fibers. Magnetic susceptibility measurements demonstrated that the hysteretic spin transition is preserved in all composites, with a significant broadening of their coercive fields. The most significant effect is observed in the cooling mode of the composites based on nanoparticles of bigger size, 2 and 3, which is shifted to lower temperatures compared to their powder counterparts. A contrasting analysis of electrospun fibers and drop-casted films highlighted enhanced magnetic hysteresis and improved fiber stability, indicating a matrix geometry effect on spin crossover behavior. These findings underscore the potential of electrospun spin-crossover composite materials not only for creating flexible and scalable functional fabrics but also for precisely tailoring magnetic properties and enhancing robust spin-crossover behavior.