The role of the cooperative Jahn-Teller effect in the charge-ordered La_(1-x)Ca_(x)MnO_(3) (0.5≤x≤0.87) manganites

摘要

Based on the magnetoresistance, magnetization, ultrasound, and crystallographic data, we studied the role of the cooperative Jahn-Teller (JT) effect in the charge-ordered (CO) state for La_(1-x)Ca_(x)MnO_(3). We found that, with increasing the fraction of Q_(3) mode of JT distortion and decreasing that of Q_(2) mode in the CO state, the magnetic structure evolves from charge-exchange-type to C-type and the orbital ordering changes from 3d_(x~(2)-r~(2))/3d_(y~(2)-r~(2))-type to 3d_(z~(2)-r~(2))-type, with the strength of ferromagnetism and the phase separation tendency being suppressed. At the same time, the stability of the CO state and the cooperative JT lattice distortion increase. These effects imply that the cooperative JT effect with different vibration modes is the key ingredient in understanding the essential physics of the CO state.