] nanocrystals embedded in different polymeric matrices, including Poly(methyl methacrylate) (PMMA), Polyethylene glycol 6000 (PEG-6000), and Polyvinylpyrrolidone K-30 (PVP K-30). The resulting nanostructures are phase-pure, well-crystallized and exhibit a tetragonal phase. High-resolution transmission electron microscopy (HRTEM) confirms that the nanostructures are nearly square-shaped, with well-defined sizes. The abrupt, incomplete, and gradual nature of the thermal spin relaxation behavior observed from the magnetic data for pure, doped, and polymer-embedded nanocrystals is collectively explained by the local and long-range fluctuations in the crystal fields experienced by the Fe(II) spin-crossover centers, variation in nucleation barrier energy influencing elastic properties, kinetic effects linked to modification in nucleation preferential sites during spin-state switching, as well as chemical pressure, lattice-strains and imperfections, thus altering the in-plane and out-of-plane interactions that influence the cooperativity variation and are responsible for the relative stabilization of the high-spin or low-spin states by modifying the . A 3D mechanoelastic model is employed to interpret the observed magnetic behavior of pure, doped, and polymer-embedded nanocrystals, offering deeper insights into the underlying mechanisms governing spin-state transitions at the nanoscale.
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Das et al. (2025) studied this question.