The role of the cooperative Jahn-Teller effect in the charge ordered La1-xCaxMnO3 (0.5<=x<=0.87) manganites

Based on the magnetoresistance, magnetization, ultrasound, and crystallographic data, we studied the role of the cooperative Jahn-Teller effect in the charge ordered (CO) state for La1-xCaxMnO3. We found that, with increasing the fraction of Q3 mode of Jahn-Teller distortion and decreasing that of Q2 mode in the CO state, the magnetic structure evolves from CE-type to C-type and the orbital ordering changes from 3d(x2-r2)/3d(y2-r2)-type to 3d(x2-z2)-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 Jahn-Teller lattice distortion increase. These effects imply that the cooperative Jahn-Teller effect with different vibration modes is the key ingredient in understanding the essential physics of the CO state.