Near-Room-Temperature Magnetoelectric Coupling via Spin Crossover in an Iron(II) Complex

Magnetoelectric coupling is achieved near room temperature in a spin crossover Fe^II molecule-based compound, [Fe(1bpp)₂](BF₄)₂. Large atomic displacements resulting from Jahn–Teller distortions induce a change in the molecule dipole moment when switching between high-spin and low-spin states leading to a step-wise change in the electric polarization and dielectric constant. For temperatures in the region of bistability, the changes in magnetic and electrical properties are induced with a remarkably low magnetic field of 3 T. This result represents a successful expansion of magnetoelectric spin crossovers towards ambient conditions. Moreover, the observed 0.3–0.4 mC m⁻² changes in the H-induced electric polarization suggest that the high strength of the coupling obtained via this route is accessible not just at cryogenic temperatures but also near room temperature, a feature that is especially appealing in the light of practical applications.