Inverse Jahn-Teller transition in bimetallic oxalates

Because of the competition between the spin-orbit coupling and the Jahn-Teller (JT) energies in Fe(II)Fe(III) bimetallic oxalates, we theoretically predict that an undistorted phase with C(3) symmetry about each Fe site may be recovered at low temperatures. Both lower and upper JT transitions bracketing the ferrimagnetic transition temperature T(c) are predicted for compounds that exhibit magnetic compensation. Comparisons with recent measurements and first-principles calculations provide strong evidence for the inverse JT transition below T(c).