Spontaneous Strain-Spin Transition Coupling Molecular Crystal with Thermal Magnetic Memory Effect, Anisotropic High-κ...

Materials that exhibit controllable changes in electrical, magnetic, or spontaneous strain properties, particularly those that couple these functionalities simultaneously, hold significant potential for technological applications. In this study, a 1D phase transition ion-pair compound is investigated, triethylmethylammonium bis(1,2-maleonitriledithiolato)nickelate (abbr. [Et₃MeN][Ni(mnt)₂], 1), composed of flexible Et₃MeN⁺ cation and planar radical [Ni(mnt)₂]^- anion. This salt undergoes a paraelastic-ferroelastic phase transition at ≈233/224 K (on heating/cooling), driven by spin-lattice interactions. Importantly, the phase transition couples spontaneous strain, bistable magnetism with switchable dielectric properties. Another distinctive feature of 1 is its pronounced dielectric anisotropy and high dielectric permittivity, which arise due to a barrier layer capacitor effect due to cation displacement polarization and significant electron polarization of the highly conjugated anions. These findings provide a versatile molecular design strategy for developing magnetoelectric and mechanically multifunctional materials, with promising applications in next-generation electronic and smart devices that leverage coupled physical properties.