Crystal and magnetic structural study of theLa1−xCaxMnO3compound(x=34)

Abstract

We studied the crystal and magnetic structure of the ${\mathrm{La}}_{1∕4}{\mathrm{Ca}}_{3∕4}\mathrm{Mn}{\mathrm{O}}_{3}$ compound using ultrahigh resolution synchrotron x-ray and neutron-diffraction techniques. The experimental results revealed that the particular compound undergoes a structural transition at ${T}_{\mathrm{CO}}=220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This transition results in an increase of the orthorhombic splitting and the appearance of superlattice diffraction peaks, which can be indexed assuming a supercell $4a$ ($a$ is the unit cell parameter for $T>{T}_{\mathrm{CO}}$). This transition is reminiscent of those observed for the $x=1∕2$ and $x=2∕3$ stoichiometries where superstructures with $2a$ and $3a$, respectively, have been observed. At ${T}_{N}=160\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the neutron-diffraction patterns exhibit additional diffraction peaks, corresponding to antiferromagnetic long-range order with propagation vectors $\mathbf{k}=[\frac{1}{4},0,\frac{1}{2}]$ and $\mathbf{k}=[\frac{1}{2},0,\frac{1}{2}]$. In addition to the structural transition at ${T}_{\mathrm{CO}}$ the synchrotron high resolution x-ray diffraction patterns revealed a three phase coexistence.