Reentrant metal-insulator transition in the Cu-doped manganitesLa1−xPbxMnO3(x∼0.14)single crystals

Abstract

Single crystals of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Pb}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}y\ensuremath{-}z}{\mathrm{Cu}}_{y}{\mathrm{O}}_{3}$ ($x\ensuremath{\sim}0.14$; $y=0$,0.01,0.02,0.04,0.06; $z=0.02$,0.08,0.11,0.17,0.20) are grown by the flux growth technique. The effect of Cu doping at the Mn-site on magnetic and transport properties is studied. All studied samples undergo a paramagnetic-ferromagnetic transition. The Curie temperature ${T}_{C}$ decreases and the transition becomes broader with increasing Cu-doping level. The high-temperature insulator-metal (I-M) transition moves to lower temperature with increasing Cu-doping level. A reentrant M-I transition at the low temperature ${T}^{*}$ is observed for samples with $y\ensuremath{\geqslant}0.02$. In addition, ${T}^{*}$ increases with increasing Cu-doping level and is not affected by applied magnetic fields. Accompanying the appearance of ${T}^{*}$, there exists a large, almost constant magnetoresistance (MR) below ${T}^{*}$ except for a large MR peak near ${T}_{C}$. This reentrant M-I transition is ascribed to charge carrier localization due to lattice distortion caused by the Cu doping at Mn sites.