Plasma-induced magnetic phase in 3D MnII-NbIV octacyanidometalate with magnetic sponge behavior

A new magnetic phase with TC = 72 \ K was obtained by exposing the three-dimensional \ [MnII(H₂O)₂]₂[NbIV(CN)₈] · 4H₂O \ ₙ coordination ferrimagnet (TC = 49 \ K) to air, oxygen, nitrogen, and argon-based plasma. The X-ray powder diffraction pattern revealed that the unit cell shrank after plasma treatment, leading to a 20% enhancement of the superexchange couplings, as estimated from the mean-field approximation (MFA) model. Although no stable dehydrated form was found in the thermogravimetric analysis, the observed changes are attributed to the removal of crystallization water molecules. The plasma-induced magnetic phase could not be obtained by exposing the studied material to 0% relative humidity during dynamic vapor sorption. Instead, the material underwent a major structural reorganization after dehydration, necessitating an extended MFA model to reproduce the magnetic susceptibility. These findings demonstrate that plasma-induced changes can create unique magnetic phases in molecule-based systems that are otherwise unobtainable.