  Three high-spin phases recently discovered in the spin-crossover system
Mn(taa) are identified through analysis by a combination of first-principles
calculations and Monte Carlo simulation as a low-temperature Jahn-Teller
ordered (solid) phase, an intermediate-temperature dynamically correlated
(liquid) phase, and an uncorrelated (gas) phase. In particular, the Jahn-Teller
liquid phase arises from competition between mixing with low-spin impurities,
which drive the disorder, and inter-molecular strain interactions. The latter
are a key factor in both the spin-crossover phase transition and the
magnetoelectric coupling. Jahn-Teller liquids may exist in other spin-crossover
materials and materials that have multiple equivalent Jahn-Teller axes.
