Exchange interactions in the perovskites Ca 1 − x Sr x MnO 3 and R MnO 3 ( R = L a , P r , S m )

摘要: Measurement of the variation N\'eel temperature ${T}_{N}$ with pressure P and compressibility \ensuremath{\kappa} orbitally ordered $\mathrm{Mn}(\mathrm{III}){\mathrm{O}}_{3}$ array $R{\mathrm{MnO}}_{3}$ family $(R=\mathrm{L}\mathrm{a},\mathrm{P}\mathrm{r},\mathrm{S}\mathrm{m})$ $\mathrm{Mn}(\mathrm{IV}){\mathrm{O}}_{3}$ ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system have enabled determination for each a systematic increase in \ensuremath{\kappa}, magnitude Bloch parameter ${\ensuremath{\alpha}}_{B}\ensuremath{\equiv}d\mathrm{ln}{T}_{N}/d\mathrm{ln}V,$ decreasing bending (180\ifmmode^\circ\else\textdegree\fi{}-\ensuremath{\varphi}) Mn-O-Mn bond angles. The data demonstrate that anomalously high value $\ensuremath{-}{\ensuremath{\alpha}}_{B}=5.5$ reported previously ${\mathrm{LaMnO}}_{3}$ is not due to orbital order its attendant anisotropic magnetic order. A higher $|{\ensuremath{\alpha}}_{B}|$ than 3.3 an increasing characterize on approach from localized-electron side first-order transition localized itinerant electronic behavior. Moreover, puzzling empirical relationship ${T}_{N}\ensuremath{\sim}〈{\mathrm{cos}}^{2}\ensuremath{\varphi}〉$ \ensuremath{\pi}-bonding rationalized by dominance semicovalent exchange term over superexchange perturbation theory spin-spin interatomic interactions. also provide indirect evidence in-phase out-of-phase stacking along c axis (001)-plane ordering has been predicted Mizokawa, Khomskii, Sawatzky.