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

TL;DR

This study investigates the transition between ferromagnetic metallic and charge-ordered insulating states in Pr0.65(CaySr1-y)0.35MnO3, demonstrating phase segregation on mesoscopic scales rather than a quantum critical point.

Contribution

It provides evidence that the transition involves phase coexistence and segregation, challenging the quantum critical point scenario in this manganite system.

Findings

Phase segregation occurs on mesoscopic scales.

No significant charge-disordered paramagnetic phase at low temperatures.

Phase boundary depends on temperature and composition.

Abstract

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.