Pressure effects on the transport and magnetic properties ofLa1.4Sr1.6Mn2O7

Abstract

The effects of external (hydrostatic) pressure and internal (chemical) pressure on the transport and magnetic properties of the ${\mathrm{La}}_{1.4}{\mathrm{Sr}}_{1.6}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ are investigated. Both metal-insulator transition temperature ${T}_{m}$ and Curie temperature ${T}_{C}$ increase with the increase of external pressure. In contrast, the ${T}_{m}$ and ${T}_{C}$ decrease with the increase of Ca content in ${\mathrm{La}}_{1.4}{(\mathrm{S}\mathrm{r}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{)}_{1.6}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7} (x<~0.3),$ where the internal pressure is supposed to be introduced. External pressure enlarge the ferromagnetic metal phase through the pressure-enhanced transfer interaction of the charge carriers. The Mn-O-Mn bond angle remains almost unchanged with the increase of Ca content which is in sharp contrast to the ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system. The Mn-O(3) bond length is decreased by the external pressure while increased by the internal pressure. It is interpreted that the opposite behaviors of ${T}_{m}$ and ${T}_{C}$ for external and internal pressures are due to the different variations of Mn-O(3) bond length. All other results are discussed and compared with those in the ${(\mathrm{L}\mathrm{a},\mathrm{S}\mathrm{r})\mathrm{MNO}}_{3}$ system.