Effect of chemical pressure induced by La3+/Y3+ substitution on the magnetic ordering of (AMn3)Mn4O12 quadruple perovskites

We report on the successful high-pressure synthesis of single-phase powders of the quadruple perovskite $({\mathrm{YMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$, where the chemical pressure exerted by the small ${\mathrm{Y}}^{3+}$ ion is expected to enhance the exchange interaction between ${\mathrm{Mn}}^{3+}$ ions. According to this expectation, powder neutron diffraction, specific heat, and magnetization measurements give evidence of a C-type antiferromagnetic ordering of the ${\mathrm{Mn}}^{3+}$ ions in the octahedrally coordinated $B$ sites at ${T}_{N,B}=108\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, 30 K higher than in the isostructural and isovalent compound, $({\mathrm{LaMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$. Surprisingly, we found no evidence of long-range magnetic order of the square-coordinated ${A}^{\ensuremath{'}}$ sites, although an indication of latent magnetic order is given by a broad peak of the DC magnetization between 70 and 40 K and by a sharp peak in the AC susceptibility at ${T}^{*}=70\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. A further unexpected feature of $({\mathrm{YMn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$, not found in previously reported $(A{\mathrm{Mn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ compounds, is a second-order structural phase transition at ${T}_{s}=200\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, attributed to a partial redistribution of charge involving both the $B$ and ${A}^{\ensuremath{'}}$-site ${\mathrm{Mn}}^{3+}$ ions. The present results suggest the existence of competing magnetic orderings, which may be linked to the occurrence of magnetic ferroelectricity in the $(A{\mathrm{Mn}}_{3}){\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ system.