PHYSICAL REVIEW B 85, 104107 (2012) Impact of Jahn-Teller active Mn 3+ on strain effects and phase transitions in Sr 0.65 Pr 0.35 MnO 3 Teck-Yee Tan, Brendan J.Kennedy, * Qingdi Zhou, and Christopher D. Ling The School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia Wojciech Miiller The School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia and Bragg Institute, ANSTO, PMB1 Menai 2234 NSW, Australia Christopher J. Howard The School of Physics, The University of Sydney, Sydney, NSW 2006, Australia Michael A. Carpenter Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom Kevin S. Knight ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom (Received 6 November 2011; revised manuscript received 10 February 2012; published 19 March 2012) 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 3m perovskite to a tetragonal I 4/mcm structure at 750 K. The Pm 3m ↔ 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 t 0.5 ∝ (T c − 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) μ 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. DOI: 10.1103/PhysRevB.85.104107 PACS number(s): 61.05.fm, 64.60.Ej, 61.50.Ks I. INTRODUCTION Mixed-valent Mn perovskites of the type Ln 1−x A x MnO 3 , where Ln is a lanthanide and A a divalent cation, have been the subject of enormous research effort for over 50 years, 1 with the discovery of colossal magnetoresistance (CMR) in such oxides driving much of the more recent interest. 2 The rich diversity in electrical, magnetic, and structural phenomena displayed by such oxides is testament to the intricate interplay between the orbital, spin, charge, and lattice degrees of freedom in these oxides. This is in contrast to the behavior of traditional ferromagnets, such as Co, Ni, and Fe, used in many devices where the spin system is isolated from the lattice. 3 In addition to their great potential for magnetic storage technology, A-site doped manganite perovskites have been widely stud- ied as cathode materials for use in solid oxide fuel cells (SOFCs). 4–6 An important feature of the mixed valence Mn 3+ /Mn 4+ manganates is the long-range orbital ordering that arises as a consequence of a Jahn–Teller (JT) type distortion of the formally Mn 3+ cations. It is generally accepted that replacing the trivalent lanthanide cation with a divalent alkaline earth cation introduces a mixed valence Mn 3+ and Mn 4+ array 7–9 where the charge can hop from Mn to Mn via the bridging oxygen anions. A consequence of the relatively large difference in the size of the Mn 3+ and Mn 4+ cations (ionic radii of 0.645 vs 0.53 ˚ A, respectively, in a six-coordinate geometry 10 ), together with the JT distortion, is that such a substitution is likely to introduce strains into the lattice. However, very little is known about the coupling between the various strains present in such complex oxides. The present contribution focuses on one member of the well-studied Sr 1−x Pr x MnO 3 series, 7,11–13 namely Sr 0.65 Pr 0.35 MnO 3 . Cubic SrMnO 3 has a G-type antiferromag- netic (AFM) ground state, 12 whereas PrMnO 3 is orthorhombic in Pnma and is an A-type AFM. 14 Knizek et al. 7 have previously described the structural, magnetic, and transport properties of several members in the series (x = 0.15–0.55) using neutron and x-ray diffraction methods. At low Pr levels (x  0.15), the oxides are isostructural with cubic SrMnO 3 in space group Pm 3m. Increasing the Pr content (0.25  x  0.52) produces a tetragonal structure in I 4/mcm, while the oxides with Pr contents in the range (0.52 <x  0.55) are orthorhombic in Imma. At still higher Pr contents, the orthorhombic Pnma structure is encountered. 15 This sequence of structures reflects differences in the cooperative tilting of the corner-sharing MnO 6 octahedra and can be correlated with changes in the tolerance factor t = (r A + r O )/ √ 2(r B + r O ), where r A , r B , and r O are the ionic radii of the A, B , and 104107-1 1098-0121/2012/85(10)/104107(10) ©2012 American Physical Society