Water-induced ferromagnetism in cobalt acetylide CoC2 nanoparticles

Transition metal acetylide CoC2 is highly absorbent of water due to its ionic character. In the anhydrous phase, CoC2 forms NaCl-like cubic structure where the orientation of C22- dianions are disordered. Once the material is exposed to air or water, the lattice of CoC2 is expanded anisotropically by the absorbed water, which restricts the orientation of C22- dianions. The magnetism of CoC2 also changes drastically by air/water exposure owing to the orientation ordering of C22- dianions. The anhydrous CoC2 behaves as superparamagnet down to 1.8 K because the magnetic domains of CoC2 are cut into pieces by orientation disorder of C22- dianions, while the hydrous CoC2 shows the ferromagnetism thanks to the large ferromagnetic domains caused by the orientation ordering of C22- dianions.

Graphical abstractNew molecule-based magnet CoC2 shows water-induced ferromagnetism caused by the orientation ordering of C22- molecules. In the anhydrous phase, the orientation of C22- is disordered, resulting in the small ferromagnetic domain and superparamagnetism. Once the material absorb the water, the orientation of C22- is ordered and the ferromagnetic domains expand, resulting in the ferromagnetic behavior.Figure optionsDownload full-size imageDownload as PowerPoint slide