Structural and magnetic ordering in Pr0.65(CaySr1-y)0.35MnO3:: Quantum critical point versus phase segregation scenarios -: art. no. 144412

The phase diagram of Pr-0.65(CaySr1-y)(0.35)MnO3, 0.6less than or equal toyless than or equal to0.8, 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.