Anomalous variation ofA-type antiferromagnetic order and two-dimensional ferromagnetic fluctuation in orbital-orderedLa1−xEuxMnO3

Abstract

A-type antiferromagnetic (AF) order with a two-dimensional (2D) ferromagnetic short-range fluctuation was observed in the stoichiometric orthorhombic ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Eu}}_{x}{\mathrm{MnO}}_{3+\ensuremath{\delta}}$ system $(0l~xl~1,$ $\ensuremath{\delta}\ensuremath{\sim}0$ with trivalent ${\mathrm{Mn}}^{3+}).$ The observation of strong basal plane ferromagnetic coupling of the A-type AF order with fluctuation above antiferromagnetic N\'eel temperature ${T}_{N}$ strongly indicates a C-type orbital ordering of ${e}_{g}$ electrons at higher temperature throughout the whole system. Anomalous decrease of ${T}_{N}$ from 139 K for ${\mathrm{LaMnO}}_{3},$ to 91 K for ${\mathrm{La}}_{0.5}{\mathrm{Eu}}_{0.5}{\mathrm{MnO}}_{3}$ and down to 42 K for ${\mathrm{EuMnO}}_{3}$ is the result of weaker anisotropic superexchange interaction due to stronger Jahn-Teller lattice distortion in orbital-ordered ${\mathrm{EuMnO}}_{3}$ from power x-ray Rietveld analysis and Mn K-edge x-ray absorption near-edge structure spectroscopic study.