Verwey ordering on magnetite as a co-operative Jahn-Teller transition

Verwey ordering of Fe²⁺ and Fe³⁺ on alternate planes along [001] direction occurring at 119° K is considered uniquely as a collective Jahn-Teller transition. The model predicts two successive second-order transitions, as a result of simultaneous coupling to both shear distortion and optical phonon mode. Expected elastic constant anomalies are calculated. The insulating state thus obtained at T = 0, does not invoke electron-electron correlation on near-neighbor sites.