Unexpected Light-Induced Thermal Hysteresis in Matrix Embedded Low Cooperative Spin Crossover Microparticles

• Main Authors: Diana Plesca, Anastasia Railean, Radu Tanasa, Alexandru Stancu, Jérôme Laisney, Marie-Laure Boillot, Cristian Enachescu
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Magnetochemistry
• Subjects: spin-crossover; light-induced; hysteresis; first-order reversal curves; glycerol matrix
• Online Access: https://www.mdpi.com/2312-7481/7/5/59

The embedding of spin-crossover micro- or nanocrystals in various surroundings dramatically changes their functionalities based on first-order spin transitions. The dampening of their internal cooperativity, together with introducing a new kind of interactions occurring at interfaces between spin-crossover particles and their environment, results in spectacular effects, as an enhanced hysteresis with non-cooperative transitions. In this work, we deal with the influence of the embedding matrix on the light-induced thermal hysteresis (LITH) in the case of spin-crossover microparticles of Fe(phen)₂(NCS)₂. Despite the low cooperativity of this compound, the competition between the continuous photoexcitation towards the metastable high spin state and the relaxation down to low spin ground state leads to a light-induced thermal hysteresis, with a quasi-static width of around 10 K. This unexpected hysteresis is explained by considering a switch-on/cutoff mechanism of the particle–matrix interactions in the framework of a mean-field approach based on negative external pressures, with Gaussian distributed variations and of an Ising-like model with various interactions with the environment. Additional first-order reversal curves measurements and corresponding calculated distributions are in line with relaxations under light and confirm the existence of a non-kinetic LITH.