Reehuis, M.; Ulrich, C.; Abdala, P.M.; Pattison, P.; Khaliullin, G.; Fujioka, J.; Miyasaka, S.; Tokura, Y.; Keimer, B.: Spin and orbital disordering by hole doping in Pr1-xCaxVO3. Physical Review B 94 (2016), p. 104436/1-11
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High-resolution powder x-ray diffraction and single-crystal neutron diffraction were used to investigate the crystal structure and magnetic ordering of the compound Pr1−xCaxVO3 (0≤x≤0.3), which undergoes an insulator-to-metal transition for x∼0.23. Since the ionic radii of Pr3+ and Ca2+ are almost identical and structural disorder is minimal, Pr1−xCaxVO3 is a good model system for the influence of hole doping on the spin and orbital correlations in transition metal oxides. The end member PrVO3 is a Mott-Hubbard insulator, which exhibits a structural phase transition at TS=180K from an orthorhombic to a monoclinic structure with space groups Pbnm and P21/b, respectively. This transition is associated with the onset of orbital ordering and strong Jahn-Teller distortions of the VO6 octahedra. Antiferromagnetic C-type order with vanadium moments oriented in the ab plane is observed below TN=140K. Upon cooling, the vanadium moments induce a progressive magnetic polarization of the praseodymium sublattice, resulting in a ferrimagnetic structure with coexisting modes (Cx, Fy) and (Fx, Cy). In the insulating range of the Pr1−xCaxVO3 phase diagram, Ca doping reduces both the orbital and magnetic transition temperatures so that TS=108K and TN=95K for x=0.20. The Jahn-Teller distortions and ordered vanadium moments also decrease upon doping. In a metallic sample with x=0.30, Jahn-Teller distortions and long-range orbital ordering are no longer observable, and the average crystal structure remains orthorhombic down to low temperature. However, broadening of some lattice Bragg reflections indicate a significant increase in lattice strain. Antiferromagnetic short-range order with a weak ordered moment of 0.14(3) μB per vanadium atom could still be observed on the vanadium site below T∼60K. We discuss these observations in terms of doping-induced spin-orbital polaron formation.