Tetragonal to monoclinic transition in the metallic antiferromagnetPr0.5Sr0.5MnO3

The structural changes associated with the ferromagnetic (FM)/metallic to antiferromagnetic (AFM)/insulating transition of ${\mathrm{Pr}}_{1/2}{\mathrm{Sr}}_{1/2}{\mathrm{MnO}}_3\hspace{0.5em}(I4/mc\overrightarrow{m}{P2\mathrm{}}_1/n)$ are described in detail. Based on high-resolution neutron-diffraction data, in the ${P2\mathrm{}}_1/n$ phase Mn1 and Mn2 octahedra have the same charge and are identically deformed. The electronically induced transition to the antiferromagnetic A-type structure at $T_N$ is the result of a stretchinglike distortion of the octahedra that (i) contracts the Mn-O2 bond perpendicular to the FM planes by deviating $\beta$ from $90°$ and (ii) injects electrons into Mn-O1 and Mn-O3 bonds. The observed microscopic changes are completely different to the structural transition in the A-type ${\mathrm{LaMnO}}_3$ and are discussed in the light of the orbital polarization previously proposed.