Magnetotransport properties and magnetostructural phenomenon in single crystals ofLa0.7(Ca1−ySry)0.3MnO3

Abstract

The magnetotransport and magnetostructural properties of ${\mathrm{La}}_{0.7}({\mathrm{Ca}}_{1\ensuremath{-}y}{\mathrm{Sr}}_{y}{)}_{0.3}{\mathrm{MnO}}_{3}$ $(0l~yl~1)$ are studied. We investigate the variation in magnetoresistance (MR) with y and the field-induced structural transition at $y\ensuremath{\sim}0.5$ by using single crystals prepared by the floating-zone method. With the increase in y, the colossal MR behavior at $y\ensuremath{\sim}0$ is transformed to a rather canonical MR (a MR free from lattice effects) at $y=1.$ The coefficient C in the empirical relation that $\ensuremath{\rho}(M)/\ensuremath{\rho}(0)=\mathrm{exp}[\ensuremath{-}{C(M/M}_{s}{)}^{2}]$ (M and ${M}_{s}$ being the magnetization and its zero-temperature saturation value) shows a significant change with y, attainable for example, from 7.6 at $y=0.1$ to 2.3 at $y=0.7.$ As an example of the magnetoswitching of a crystal structure around room temperature, the structural-phase transition induced by an external magnetic field is investigated for crystals with $y\ensuremath{\sim}0.5.$ Structural-phase diagrams of the magnetic field vs temperature plane are given.