Jahn-Teller Solid, Liquid and Gas spin Spin-crossover System Mn(taa)*

Magnetoelectric coupling is of fundamental interest to understanding spin-charge-lattice interactions,
however also has potential for applications in spintroics for moving beyond Moore's law. The lower Young's modulus in molecule-based materials offers great potential for lattice-mediated magnetoelectric coupling. The molecular magnet Mn(taa) is a spin-crossover system where the spin-state has a phase transition between low-spin state to high-spin state around 45 K. Recently, the magnetoelectric coupling was observed in Mn(taa). Here, we investigated the microscopic origin of the phase transition and magnetoelectric coupling in spin-crossover system Mn(taa) via first-principles and Monte Carlo simulation. DFT calculations indicate that phonon play a key role during spin-crossover transition. Monte Carlo simulations using parameters from DFT and experimental data yield new physical insights into various phases observed experimentally. Jahn-Teller gas, liquid, and solid phases are defined according to the degrees of correlation in the polarization.