Impact of Jahn-Teller active Mn3+on strain effects and phase transitions in Sr0.65Pr0.35MnO3

Abstract

The mixed-valence manganite Sr${}_{0.65}$Pr${}_{0.35}$MnO${}_{3}$ has been prepared and its crystal and magnetic structure investigated between 7 and 1200 K using high-resolution powder neutron diffraction. The structural and lattice parameter data have been used to determine the octahedral tilting and spontaneous strains associated with the structural, electronic, and magnetic phase transitions. At room temperature, the structure is tetragonal and is characterized by cooperative out-of-phase tilts of the MnO${}_{6}$ octahedra about the $c$ axis and a large Jahn--Teller-type distortion due to the presence of Mn${}^{3+}$. The sample exhibits a reversible phase transition from the cubic $Pm\overline{3}m$ perovskite to a tetragonal $I$4/mcm structure at 750 K. The $Pm\overline{3}m$ \ensuremath{\leftrightarrow} I4/mcm phase transition is continuous, and the tetragonal strain, which is dominated by the Jahn--Teller-type distortion of the MnO${}_{6}$ octahedra, exhibits an unusual ${e}_{\mathrm{t}}$${}^{0.5}$ \ensuremath{\propto} (${T}_{c}$ $\ensuremath{-}$ $T$) temperature dependence. At low temperatures, a C-type antiferromagnetic structure develops with a Neel temperature ${T}_{N}$ of 250 K. The Mn magnetic moment at 7 K is 2.99(2) ${\ensuremath{\mu}}_{B}$/Mn. The magnetic ordering introduces additional tetragonal strain, and this strain shows the expected quadratic dependence on the magnetic moment at low temperatures. An increase in the octahedral tilt angle at ${T}_{N}$ demonstrates an effective coupling between the magnetic ordering process and octahedral tilting.