Effect of oxygen isotope substitution and crystal micro-structure on magnetic ordering and phase separation in {$ m (La_{1-y}Pr_{y})_{0.7}Ca_{0.3}MnO_3$}

摘要

The crystal and magnetic structures of the specified CMR manganite systemhave been studied as a function of $y=(0.2-1)$ across the metal-insulator (MI)transition, and of the oxygen mass ($^{16}$O, $^{18}$O). We quantitatively showhow the polaronic narrowing of the carrier bandwidth and the crystal latticemicro-strains control the volume fractions of the mesoscopic ferro- andantiferromagnetic clusters. A well-defined dip in the transition temperaturesand the suppression of all the types of long range ordering seen near theMI-transition at $y\simeq0.9$ indicate a key role of the quenched disorder forthe formation of the long-scale phase separated state.