Irreversible change of electric conduction in ionic-liquid-gated (La,Sr)MnO3 thin films

We have investigated the ionic-liquid-gating effect on electric conduction in (La 0.8 Sr 0.2 )MnO 3 (LSMO) thin films. The gating effect is significant for the LSMO thin films grown at low oxygen partial pressures. We observed that the channel resistance of LSMO was altered only for a positive gating voltage, not for a negative one, mainly through the changes of mobility rather than the carrier density. The increased sheet resistance at positive voltage does not return to the original value even after the removal of gating voltage as well as the application of a negative voltage. Through the Mn 2 p X-ray absorption, the increased resistance of LSMO after a positive voltage is found to be associated with the increase of the Mn 3+ ions over Mn 4+ ones. We proposed that oxygen vacancy and electrochemical reactions should play a role for the irreversible electric conduction in ionic-liquid-gated (La,Sr)MnO 3 thin films.