The high temperature Jahn-Teller transition in LaMn7O12

A first order structural Jahn-Teller transition at TJT ? 650K has been recently reported for the quadruple perovskite LaMn7O12 . We have carried out magnetization and transport measurements below and above TJT in order to investigate the effect of the transition. Electrical conduction turns out to be polaronic, changing from non-adiabatic to adiabatic through the transition. Magnetic behavior can be described by non-interacting Mn3+ ions below TJT , while above TJT it is of questionable interpretation. The effect of thermal cycling on as grown samples of different purity degree also allowed us to clarify the intrinsic magnetic response of LaMn7O12 at lower temperatures.