Externally stimulated magnetic materials are essential for next-generation memory and sensing technologies; however, tristate magnetic switching remains rare. This study presents a cyanide-bridged pentadecanuclear spin-cluster, Ni9W(CN)86(pyrazole)18(H2O)6·zH2O (Ni9W6), which exhibits reversible humidity-induced tristate magnetic switching. The material is paramagnetic at 75% relative humidity (RH), ferromagnetic (Curie temperature = 11 K) at 11% RH, and displays interacting superparamagnetic (blocking temperature = 13 K) at 0% RH. The adsorption and desorption of in-layer crystallization water modulate the number of superexchange interaction pathways linking discrete Ni9W6 clusters, directly tuning intercluster magnetic coupling without altering the cluster framework or electronic states. Complete dehydration induces reversible nanoscale cracking, whereby crystals are divided into 6-8 nm magnetic nanodomains that interact via dipolar forces to yield the interacting superparamagnetic state. This water-mediated control of superexchange pathways and reversible formation of nanoscale magnetic regions achieved in a self-healing spin material provide a design strategy for multistate stimuli-responsive functional materials.
Akagi et al. (Tue,) studied this question.