Structure-properties phase diagram for La_1-xSr_xMnO₃ (0.1<~x<~0.2)

By combining the results of magnetization, resistivity, and neutron powder-diffraction data for stoichiometric La_1-xSr_xMnO₃, we have constructed a phase diagram that describes the magnetic, transport, and structural properties and the relationships among them as a function of composition (0.1<~x<~0.2) and temperature (10–340 K). We show that, with increasing Sr content, the Curie temperature increases linearly, while the temperature of an orbital ordering transition to a state with a large coherent Jahn-Teller (JT) distortion decreases. These two phase-transition lines cross at x=0.145 and T=210 K. When the transition to the ferromagnetic state occurs in a phase that has a large coherent JT distortion (x<0.145), a strong magnetolattice coupling is observed; the coherent JT distortion is dramatically reduced and the incoherent distortion is enhanced in the ferromagnetic phase. For x>0.145, where the coherent JT distortion is small above Curie temperature, magnetolattice coupling reduces the incoherent distortion at T_C and strongly suppresses the transition to a phase with a large coherent JT distortion. These observations are consistent with a competition between ferromagnetism and JT distortion that is mediated by a colossal spin-charge-lattice coupling. A metallic state occurs below the Curie temperature when both coherent and incoherent JT distortions are suppressed.