Multiphase segregation and metal-insulator transition in single crystal La5/8−yPryCa3/8MnO3

Abstract

The insulator-metal transition in single crystal ${\mathrm{La}}_{5/8-y}{\mathrm{Pr}}_y{\mathrm{Ca}}_{3/8}{\mathrm{MnO}}_3$ with $y\approx 0.35$ was studied using synchrotron x-ray diffraction, electric resistivity, magnetic susceptibility, and specific heat measurements. Despite the dramatic drop in the resistivity at the insulator-metal transition temperature $T_{\mathrm{MI}},$ the charge-ordering (CO) peaks exhibit no anomaly at this temperature and continue to grow below $T_{\mathrm{MI}}.$ Our data suggest then, that in addition to the CO phase, another insulating phase is present below $T_{\mathrm{CO}}.$ In this picture, the insulator-metal transition is due to the changes that occur within this latter phase. The CO phase does not appear to play a major role in this transition. We propose that a percolationlike insulator-metal transition occurs via the growth of ferromagnetic metallic domains within the parts of the sample that do not exhibit charge ordering. Finally, we find that the low-temperature phase-separated state is unstable against x-ray irradiation, which destroys the CO phase at low temperatures.