Marianne Rotter

Publications of Marianne Rotter

• The structures of delta-PdCl2 and gamma-PdCl2: phases with negative thermal expansion in one direction.

  Authors: Jürgen Evers, Wolfgang Beck, Michael Göbel, Stefanie Jakob, Peter Mayer, Gilbert Oehlinger, Marianne Rotter, Thomas M Klapötke

  Angewandte Chemie (International ed. in English). 08/2010; 49(33):5677-82.

• Different response of the crystal structure to isoelectronic doping in BaFe2[As(1-x)P(x)]2 and [Ba(1-x)Sr(x)]Fe2As2

  Authors: Marianne Rotter, Christine Hieke, Dirk Johrendt

  05/2010;

  Superconductivity up to 30 K in charge neutrally doped BaFe2[As(1-x)P(x)]2 has been ascribed to chemical pressure, caused by the shrinking unit cell. But the latter induces no superconductivity inSuperconductivity up to 30 K in charge neutrally doped BaFe2[As(1-x)P(x)]2 has been ascribed to chemical pressure, caused by the shrinking unit cell. But the latter induces no superconductivity in [Ba(1-x)Sr(x)]Fe2As2 in spite of the same volume range. We show that the spin-density-wave (SDW) state of BaFe2As2 becomes suppressed in BaFe2[As(1-x)P(x)]2 by a subtle reorganization of the crystal structure, where arsenic and phosphorus are located at different coordinates z(As), z(P). High-resolution X-ray diffraction experiments with BaFe2[As(1-x)P(x)]2 single crystals reveal almost unchanged Fe-P bonds, but a contraction of the Fe-As bonds, which remain nearly unchanged in [Ba(1-x)Sr(x)]Fe2As2. Since the Fe-As bond length is a gauge for the magnetic moment, our results show why the SDW is suppressed by P-, but not by Sr-doping. Only the Fe-P interaction increases the width of the iron 3d bands, which destabilizes the magnetic SDW ground state. The simultaneous contraction of the Fe{As bonds is rather a consequence of the vanishing magnetism. Ordered structure models of BaFe2[As(1-x)P(x)]2 obtained by DFT calculations agree perfectly with the single-crystal X-ray structure determinations. The contraction of the Fe-As bonds saturates at doping levels above x = 0.3, which corrects the unreasonable linear decrease of the so-called pnictide height. Comment: 7 Pages, 8 Figures, citations added, text revised

• Competition of magnetism and superconductivity in underdoped (Ba1-xKx)Fe2As2

  Authors: Marianne Rotter, Marcus Tegel, Inga Schellenberg, Falko M. Schappacher, Rainer Poettgen, Joachim Deisenhofer, Axel Guenther, Florian Schrettle, Alois Loidl, Dirk Johrendt

  01/2009;

  Polycrystalline samples of underdoped (Ba1-xKx)Fe2As2 (x<=0.4) were synthesized and studied by x-ray powder diffraction, magnetic susceptibility, specific heat and 57Fe-Moessbauer-spectroscopy. ThePolycrystalline samples of underdoped (Ba1-xKx)Fe2As2 (x<=0.4) were synthesized and studied by x-ray powder diffraction, magnetic susceptibility, specific heat and 57Fe-Moessbauer-spectroscopy. The structural phase transition from tetragonal to orthorhombic lattice symmetry shifts towards lower temperatures, becomes less pronounced at x = 0.1-0.2 and is no longer present at x = 0.3. Bulk superconductivity is observed in all samples except (Ba0.9K0.1)Fe2As2 by resistivity and magnetic susceptibility measurements. Specific heat data show a broad SDW phase transition in (Ba0.9K0.1)Fe2As2, which is hardly discernible in (Ba0.8K0.2)Fe2As2. No SDW anomaly is found in the specific heat of optimally doped (Ba0.6K0.4)Fe2As2, where C changes by 0.1 J/K at Tc = 37.3 K. 57Fe-Moessbauer-spectra show full magnetic hyperfine field splitting, indicative of antiferromagnetic ordering at 4.2 K in samples with x = 0-0.2, but zero magnetic hyperfine field in samples with x = 0.3. The spectra of (Ba0.9K0.1)Fe2As2 and (Ba0.8K0.2)Fe2As2 in the phase transition regions are temperature-dependent superpositions of magnetic and non-magnetic components, caused by inhomogeneous potassium distribution. Our results suggest the co-existence of AF magnetic ordering and superconductivity without mesoscopic phase separation in the underdoped region and show unambiguously homogeneous superconducting phases close to optimal doping. This is in contrast to recently reported results about single crystal (Ba1-xKx)Fe2As2.

• Superconductivity at 38 K in the Iron Arsenide (Ba1-xKx)Fe2As2.

  Authors: Marianne Rotter, Marcus Tegel, Dirk Johrendt

  Physical review letters. 10/2008; 101(10):107006.

  The ternary iron arsenide BaFe2As2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. We have discovered bulk superconductivity atThe ternary iron arsenide BaFe2As2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. We have discovered bulk superconductivity at T_{c}=38 K in (Ba1-xKx)Fe2As2 with x approximately 0.4. The parent compound BaFe2As2 crystallizes in the tetragonal ThCr2Si2-type structure, which consists of (FeAs);{delta-} iron arsenide layers separated by Ba2+ ions. BaFe2As2 is a poor metal and exhibits a spin density wave anomaly at 140 K. By substituting Ba2+ for K+ ions we have introduced holes in the (FeAs);{-} layers, which suppress the anomaly and induce superconductivity. The T_{c} of 38 K in (Ba0.6K0.4)Fe2As2 is the highest in hole doped iron arsenide superconductors so far. Therefore, we were able to expand this class of superconductors by oxygen-free compounds with the ThCr2Si2-type structure.

• Superconductivity and Crystal Structures of (Ba(1-x)K(x))Fe(2)As(2) (x=0-1).

  Authors: Marianne Rotter, Michael Pangerl, Marcus Tegel, Dirk Johrendt

  Angewandte Chemie (International ed. in English). 10/2008;

• Superconductivity and Crystal Structures of (Ba1-xKx)Fe2As2 (x = 0 - 1)

  Authors: Marianne Rotter, Michael Pangerl, Marcus Tegel, Dirk Johrendt

  08/2008;

  We report on doping dependencies of structural parameters and superconducting transition temperatures in the solid solution (Ba1-xKx)Fe2As2. As the main effect of doping on the crystal structure, weWe report on doping dependencies of structural parameters and superconducting transition temperatures in the solid solution (Ba1-xKx)Fe2As2. As the main effect of doping on the crystal structure, we find linear decreasing As-Fe-As bond angles and Fe-Fe distances, equivalent to an elongation of the FeAs4 tetrahedra along [001]. The structural changes are intimately coupled to the electronic states at the Fermi level, because the most relevant Fe-3dx2-y2 orbitals are strongly affected by the As-Fe-As bond angle. Superconductivity is present over the whole doping range in (Ba1-xKx)Fe2As2 with a maximum Tc of 38 K at x ~ 0.4. The superconducting transitions in the orthorhombic compounds (Ba0.9K0.1)Fe2As2 (Tc ~ 3 K) and (Ba0.8K0.2)Fe2As2 (Tc ~ 25 K) is strong evidence for the coexistence of superconductivity with the structurally distorted and potentially magnetically ordered state in the BaFe2As2 family of iron arsenide superconductors.

• Structural and magnetic phase transitions in the ternary iron arsenides SrFe2As2 and EuFe2As2

  Authors: Marcus Tegel, Marianne Rotter, Veronika Weiss, Falko M. Schappacher, Rainer Poettgen, Dirk Johrendt

  07/2008;

  The structural and magnetic phase transitions of the ternary iron arsenides SrFe2As2 and EuFe2As2 were studied by temperature-dependent x-ray powder diffraction and 57-Fe Moessbauer spectroscopy.The structural and magnetic phase transitions of the ternary iron arsenides SrFe2As2 and EuFe2As2 were studied by temperature-dependent x-ray powder diffraction and 57-Fe Moessbauer spectroscopy. Both compounds crystallize in the tetragonal ThCr2Si2-type structure at room temperature and exhibit displacive structural transitions at 203 K (SrFe2As2) or 190 K (EuFe2As2) to orthorhombic lattice symmetry in agreement with the group-subgroup relationship between I4/mmm and Fmmm. 57-Fe Moessbauer spectroscopy experiments with SrFe2 As2 show full hyperfine field splitting below the phase transition temperature (8.91(1) T at 4.2 K). Order parameters were extracted from detailed measurements of the lattice parameters and fitted to a simple power law. We find a relation between the critical exponents and the transition temperatures for AFe2As2 compounds, which shows that the transition of BaFe2As2 is indeed more continuous than the transition of SrFe2As2 but it remains second order even in the latter case.

• Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2

  Authors: Marianne Rotter, Marcus Tegel, Inga Schellenberg, Wilfried Hermes, Rainer Pöttgen, Dirk Johrendt

  06/2008;

  The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenideThe ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase transition at 140 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (I4/mmm) to orthorhombic (Fmmm). 57Fe Moessbauer spectroscopy experiments show a single signal at room temperature and full hyperfine field splitting below the phase transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can serve as a new parent compound for oxygen-free iron arsenide superconductors.