Humidity-Induced Tristate Magnetic Switching in a Self-Healing High-Spin Cluster Material

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, Ni₉[W(CN)₈]₆(pyrazole)₁₈(H₂O)₆·<i>z</i>H₂O (<b>Ni</b>_<b>9</b><b>W</b>_<b>6</b>), 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 <b>Ni</b>_<b>9</b><b>W</b>_<b>6</b> 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.