Crystal and magnetic structures of(La0.70Ca0.30)(CryMn1−y)O3: A neutron powder diffraction study

Abstract

The crystal and magnetic structures of $({\mathrm{La}}_{0.70}{\mathrm{Ca}}_{0.30})({\mathrm{Cr}}_{y}{\mathrm{Mn}}_{1\ensuremath{-}y}){\mathrm{O}}_{3}$ for $y=0.70$, 0.50, and 0.15 have been investigated using neutron powder diffraction. The three samples crystallize in the $Pnma$ space group at both 290 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and exhibit different magnetic structures at low temperature. In $({\mathrm{La}}_{0.70}{\mathrm{Ca}}_{0.30})({\mathrm{Cr}}_{0.70}{\mathrm{Mn}}_{0.30}){\mathrm{O}}_{3}$, antiferromagnetic order with a propagation vector $\mathbit{k}=0$ sets in. The magnetic structure is ${G}_{x}$, i.e., of $G$ type with spins parallel to the $a$ axis. On the basis of our Rietveld refinement and the available magnetization data, we speculate that only ${\mathrm{Cr}}^{3+}$ spins order, whereas ${\mathrm{Mn}}^{4+}$ act as random magnetic impurities. In $({\mathrm{La}}_{0.70}{\mathrm{Ca}}_{0.30})({\mathrm{Cr}}_{0.50}{\mathrm{Mn}}_{0.50}){\mathrm{O}}_{3}$ the spin order is still of the type ${G}_{x}$, although the net magnetic moment is smaller. No evidence for magnetic order of the Mn ions is observed. Finally, in $({\mathrm{La}}_{0.70}{\mathrm{Ca}}_{0.30})({\mathrm{Cr}}_{0.15}{\mathrm{Mn}}_{0.85}){\mathrm{O}}_{3}$ a ferromagnetic ordering of the Mn spins takes place, whereas the ${\mathrm{Cr}}^{3+}$ ions act as random magnetic impurities with randomly oriented spins.