Structural and magnetic ordering in Pr0.65(CaySr1-y)0.35MnO3: Quantum critical point versus phase segregation scenarios

The phase diagram of Pr0.65(CaySr1–y)0.35MnO3, 0.6≤y≤0.8, has been determined by neutron diffraction, magnetization, and electrical conductivity measurements in order to investigate the nature of the transition between ferromagnetic metallic and charge-ordered insulating states near y = 0.75. Two possible scenarios for this transition have been proposed: a "quantum-critical-point"-like feature, near which an associated charge-disordered paramagnetic phase is present, or a phase coexistence region. We demonstrate that the latter case is true, phase segregation occurring on a mesoscopic macroscopic length scale (several hundred angstroms to several microns). Our results show that no significant amount of the charge-disordered paramagnetic phase is present at low temperatures. Our data also indicate that the charge-ordered insulator to ferromagnetic metal phase boundary is temperature as well as composition dependent.