Jahn-Teller Distortion in Bimetallic Oxalates
arXiv:0802.2678 · doi:10.1103/PhysRevLett.101.116402
Abstract
A C-symmetric crystal-field potential in the Fe(II)Fe(III) bimetallic oxalates splits the L=2 Fe(II) multiplet into two doublets and a singlet. In compounds that exhibit magnetic compensation, one of the doublets was predicted to lie lowest in energy and carry a non-quenched orbital angular momentum $\pm \ld $, where $\ld $ exceeds a threshold value. In a range of $\ld $, a Jahn-Teller (JT) distortion increases the energy splitting of the low-lying doublet and breaks the C symmetry of the bimetallic planes around the ferrimagnetic transition temperature. At low temperatures, the JT distortion disappears in compounds that display magnetic compensation due to the competition with the spin-orbit coupling. A comparison with recent measurements provides strong evidence for this re-entrant, low-temperature JT transition and a prediction for the normal, high-temperature JT transition. The size of the JT distortion is estimated using first-principles calculations, which suggest that the long-range ordering of smaller, non-C-symmetric organic cations can eliminate magnetic compensation.
7 pages, 4 figures, submitted to Journal of the American Chemical Society