Plasma-induced magnetic phase in 3D $\mathrm{M}{\mathrm{n}}^{\mathrm{II}}-\mathrm{N}{\mathrm{b}}^{\mathrm{IV}}$ octacyanidometalate with magnetic sponge behavior

Abstract

A new magnetic phase with $T_C=72\mathrm{K}$ was obtained by exposing the three-dimensional $\{[\mathrm{M}{\mathrm{n}}^{\mathrm{II}}({\mathrm{H}}_2\mathrm{O}{)}_2{]}_2[\mathrm{N}{\mathrm{b}}^{\mathrm{IV}}(\mathrm{CN}{)}_8]\cdot 4{\mathrm{H}}_2\mathrm{O}{\}}_{\mathrm{n}}$ coordination ferrimagnet ($T_C=49\mathrm{K}$) 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.

20 pages, 11 figures, 1 table