Browsing by Author "Ranjbar, B"

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    The impact of chemical doping on the magnetic state of the Sr2YRuO6 double perovskite
    (Elsevier, 2017-05-01) Kayser, P; Ranjbar, B; Kennedy, BJ; Avdeev, M
    The impact of chemical doping of the type Sr2−xAxYRuO6 (A=Ca, Ba) on the low temperature magnetic properties of Sr2YRuO6, probed using variable temperature magnetic susceptibility, neutron diffraction and heat capacity measurements, are described. Specific-heat measurements of un-doped Sr2YRuO6 reveal two features at ∼26 and ∼30 K. Neutron scattering measurements at these temperatures are consistent with a change from a 2D ordered state to the 3D type 1 AFM state. Magnetic and structural studies of a number of doped oxides are described that highlight the unique low temperature behavior of Sr2YRuO6 and demonstrate that doping destabilizes the intermediate 2D ordered state. © 2017 Elsevier Inc.
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    Magnetic and structural studies of Sc containing ruthenate double perovskites A2ScRuO6 (A = Ba, Sr)
    (American Chemical Society, 2017-07-10) Kayser, P; Injac, S; Ranjbar, B; Kennedy, BJ; Avdeev, M; Yamaura, K
    Ruthenium-containing double perovskites A2ScRuO6 have been synthesized as polycrystalline powders and structurally characterized using a combination of synchrotron X-ray and neutron powder diffraction methods. When A = Ba, a hexagonal 6L perovskite structure is obtained if the synthesis is conducted at ambient pressure and a rock-salt ordered cubic structure is obtained if the sample is quenched from high pressures. The Sr oxide Sr2ScRuO6 is obtained with a rock-salt ordered corner sharing topology. Heat capacity and bulk magnetic susceptibility measurements show that the three oxides are antiferromagnets. Cubic Ba2ScRuO6 undergoes a metal–insulator transition near 270 K and hexagonal Ba2ScRuO6 is a semiconductor with an activation energy of 0.207 eV. The magnetic structures of the two rock-salt ordered double perovskites were established using powder neutron diffraction and are described by k = (0,0,1) and k = (0,0,0) for the Ba and Sr oxides, respectively, corresponding to type I antiferromagnetic structures, with ferromagnetic layers stacked antiferromagnetically. The ambient-pressure hexagonal polymorph of Ba2ScRuO6 has partial Sc-Ru ordering at both the face-sharing B2O9 dimer and corner-sharing BO6 sites. The magnetic structure is described by k = (1/2,0,0) with the basis vector belonging to the irreducible representation Γ3. © 2017 American Chemical Society
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    Spin–orbit coupling controlled ground state in the Ir(V) perovskites A2ScIrO6 (A = Ba or Sr)
    (American Chemical Society, 2017-01-30) Kayser, P; Kennedy, BJ; Ranjbar, B; Kimpton, JA; Avdeev, M
    The structural and magnetic properties of the two Ir(V) perovskites Ba2ScIrO6 and Sr2ScIrO6 were established. The structures were refined using a combined neutron and synchrotron data set. At room temperature the former has a cubic structure in space group Fm3̅m with a = 8.1450(3) Å, and the latter is monoclinic in P21/n with a = 5.6606(3) Å, b = 5.6366(3) Å, c = 7.9720(4) Å, and β = 89.977(5)°. Magnetization measurements show both oxides have magnetic moments close to zero as a consequence of strong spin–orbit coupling that results in a Jeff ≈ 0 ground state. The distortion of the IrO6 octahedra in Sr2ScIrO6 is insufficient to generate crystal field splitting strong enough to quench the spin–orbit coupling. © 2017 American Chemical Society
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    Structural and magnetic properties of the ruthenium double perovskites Ba2−xSrxYRuO6
    (Royal Society of Chemistry, 2015-01-19) Ranjbar, B; Pavan, AF; Kennedy, BJ; Zhang, Z
    The crystal structures of the series of ordered double perovskites Ba2−xSrxYRuO6 (0 ≤ x ≤ 2) were studied by high resolution synchrotron X-ray diffraction. The materials displayed a sequence of structures image file: c4dt03682d-t1.tif associated with increasing tilting of the corner sharing octahedra. The same sequence of structures can be induced by varying the temperature of appropriate members of the series. Magnetic susceptibility measurements demonstrate the oxides to be antiferromagnets with a Neel temperature of ∼30 K. There is a simple correlation between the Weiss constant θ and the Ru–O–Y bond angle. The two Sr rich oxides (x = 1.8 and 2.0) display an, unusual, sharp minimum in susceptibility at low temperatures that is associated with the reorientation of the spins. © 2015 The Royal Society of Chemistry