Pressure effects on magnetic and transport properties of electron-dopedLa1−xCaxMnO3(x=0.8,0.9)

Abstract

Magnetic and transport properties of polycrystalline ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(x=0.8,0.9)$ perovskites were investigated in the temperature range $4.2--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, magnetic field up to $16\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and under hydrostatic pressures up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. The ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$ compound exhibits a heterogeneous spin configuration in its ground state [$G$-type antiferromagnetic (AFM) phase with local ferromagnetic (FM) regions and $C$-type AFM]. The $x=0.8$ compound is mostly an orbital ordered $C$-type AFM. In the case of ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$, an applied pressure slightly increases the magnetic transition temperature and significantly enhances the FM component. Pronounced hysteretic effects observed in ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$ may be attributed to the competition between the FM and AFM fractions in the $G$-AFM structure. On the other hand, ${\mathrm{La}}_{0.2}{\mathrm{Ca}}_{0.8}\mathrm{Mn}{\mathrm{O}}_{3}$ is insensitive to applied pressure probably due to a robustness of orbital ordered state. Resistivity data point out that AFM ordering in ${\mathrm{La}}_{0.2}{\mathrm{Ca}}_{0.8}\mathrm{Mn}{\mathrm{O}}_{3}$ occurs at temperatures below orbital ordering.