C. Ritter

Institut Laue-Langevin, Grenoble, Rhône-Alpes, France

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Publications (417)929.25 Total impact

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    ABSTRACT: We present a comparative study of the magnetic transitions in metallic Pr0.50Sr0.50CoO3 (PSCO) perovskites prepared in polycrystalline and thin film forms. As the bulk system, the strained epitaxial PSCO (010) film grown on LAO (100) is metallic in all the temperature range, with a ferromagnetic transition at 225 K, close to Tc ̃ 235 K in the ceramic PSCO specimen. Unlike the bulk system, the PSCO film does not show the second magnetic transition on cooling. In the ceramic sample, the second magnetic transition is coupled to an orthorhombic-to-monoclinic symmetry change. There is a contraction of the average ⟨Pr-O⟩ bond distance in the monoclinic phase below Ta, but the ⟨Co-O⟩ bond length is not modified across the transition. The orthorhombic to monoclinic structural transition stabilizes four short Pr-O2 bonds to basal oxygens in CoO6 octahedra. A strong hybridization of Pr 4f and O 2p orbitals in these bonds can be activated at Ta and probably assist the magnetostructural transition.
    04/2014; 115(17).
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    ABSTRACT: The oxide series La2−xSrxCoTiO6 (0 ≤x≤ 1.0) belong to the perovskite family with general formula ABO3. The evolution of the room-temperature structure as a function of the Sr content was studied using complementary techniques by applying the symmetry-adapted modes formalism (AMPLIMODES). In the compositional range presented in this article (0 ≤x≤ 0.5), the compounds adopt distorted perovskite structures of monoclinic (space group P21/n) or orthorhombic (space group Pnma) symmetry, both with octahedral tilting scheme (a−a−c+) (out of phase along two perovskite main directions and in phase along the third direction). The main difference between these structures is the existence of rock-salt order of B ions in the monoclinic symmetry, which is lost for x≥ 0.30. As the Sr content increases, a better matching of the A—O and B—O distances occurs. This is produced by an elongation of the A—O distance as La3+ is replaced by the larger ion Sr2+, and the shortening of the B—O distance due to the oxidation of Co2+ to Co3+ induced by the aliovalent substitution. As a result, the cuboctahedral A-site cavity becomes less and less distorted; the A ion tends to occupy its ideal positions, increasing its coordination and giving rise to a more symmetrical structure. In the whole compositional range, the symmetry-adapted atomic displacements (modes) responsible for the out-of-phase tilting of the BO6 octahedra remain active but those associated with the in-phase tilting become negligible, anticipating for x≥ 0.6 a transition to a new structure with tilting scheme either (a0a0c−) (space group I4/mcm) or (a−a−a0) (space group Imma) or (a−a−a−) (space group Rc).
    Journal of Applied Crystallography 04/2014; 47(2). · 3.34 Impact Factor
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    ABSTRACT: A-site-ordered perovskite Ce1/2Cu3Ti4O12 has been found to crystallize in two different forms, one with random and the other with ordered Ce/vacancy distribution at the A site of the prototype AA'3B4O12 structure. The random phase is isostructural with CaCu3Ti4O12, and the ordered phase is a new ordered derivative of the AA'3B4O12-type perovskite with two crystallographically distinct Cu sites. Although both phases form a G-type antiferromagnetic arrangement of Cu(2+) spins below 24 K, their magnetisms are quite different. A typical antiferromagnetic transition is observed in the random phase, whereas a small ferromagnetic moment appears below 24 K in the ordered phase, which rapidly decreases upon further cooling. A mean-field approximation approach revealed that this unusual behavior in the ordered phase is an L-type ferrimagnetism driven by the nonequivalent magnetizations of the two ferromagnetic Cu(2+) spin sublattices in the G-type spin structure. This unusual ferrimagnetism is a direct consequence of the Ce/vacancy ordering.
    Inorganic Chemistry 01/2014; · 4.59 Impact Factor
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    ABSTRACT: Nuclear fuel plates based on a γU-Mo/Al mixture are proposed for research reactors. In this work their thermal behavior in the [425; 550°C] temperature range has been studied mainly by neutron and high energy X-ray diffraction. Even if complementary studies will be necessary, the kinetics of first the growth of the interaction layer between γU-Mo and Al and second of the γU-Mo destabilization have been accurately measured. This basic work should be helpful for defining manufacturing conditions for fuel plates with optimized composition.
    Powder Diffraction 11/2013; 28(s2):371. · 0.54 Impact Factor
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    ABSTRACT: The synthesis and structural and magnetic characterizations of K3Fe6F19, a new iron potassium fluoride with a complex tungsten bronze related structure, are presented. This phase was found during the investigation of relatively low-temperature (600 °C) synthesis conditions of classical tetragonal tungsten bronze (TTB) fluorides and can be considered an intermediate that forms at this temperature owing to faster crystallization kinetics. The K3Fe6F19 compound has an orthorhombic structure (space group Cmcm (63), a = 7.6975(3) Å, b = 18.2843(7) Å, c = 22.0603(9) Å) related to the TTB one, where the perovskite cage is substituted by a large S-shaped channel simultaneously occupied by two potassium atoms. The magnetic structure, characterized by magnetization measurements on an oriented single crystal and powder neutron diffraction, is dominated by the presence of interconnected double stripes of antiferromagnetic triangular exchange interaction patterns alternately rotated in clock- and anticlockwise fashion. The magnetic order takes place in a wide temperature range, by increasing progressively the interaction dimensionality.
    Inorganic Chemistry 10/2013; · 4.59 Impact Factor
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    ABSTRACT: LuCuGaO4 has magnetic Cu(2+) and diamagnetic Ga(3+) ions distributed on a triangular bilayer and is suggested to undergo a spin glass transition at Tg ∼ 0.4 K. Using μSR (muon spin rotation) and neutron scattering measurements, we show that at low temperature the spins form a short range correlated state with spin fluctuations detectable over a wide range of timescales: at 0.05 K magnetic fluctuations can be detected in both the μSR time window and also extending beyond 7 meV in the inelastic neutron scattering response, indicating magnetic fluctuations spanning timescales between ∼10(-5) and ∼10(-10) s. The dynamical susceptibility scales according to the form χ″(ω)T(α), with α = 1, throughout the measured temperature range (0.05-50 K). These effects are associated with quantum fluctuations and some degree of structural disorder in ostensibly quite different materials, including certain heavy fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond glasses. We therefore suggest that LuCuGaO4 is an interesting model compound for the further examination of disorder and quantum magnetism.
    Journal of Physics Condensed Matter 09/2013; 25(35):356002. · 2.36 Impact Factor
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    ABSTRACT: The field-induced evolution of the magnetic ordering in (CuBr)Sr2Nb3O10 with a 1/3 magnetization plateau has been investigated by neutron diffraction under magnetic fields up to 10 T. With an increasing magnetic field, the zero-field helical antiferromagnetic (AFM) phase, AF1, with κ = [0 3 /8 1 /2] is replaced by a simple ferromagnetic phase with κ = [0 0 0], the formation of which is, however, retarded by the appearance of a second AFM, AF2, with κ = [0 1 /3 ∼ 0.46]. Upon further increasing of the magnetic field, the AF2 phase disappears and only the ferromagnetic phase persists. The results clearly show that the magnetization plateau, induced by the competition between field-induced ferromagnetic, F, and AF2 phases, is coincidentally situated at M = 1/3 M S of the dc magnetization curve. The AF1 and AF2 phases have strongly differing magnetic propagation vectors and are therefore not directly related.
    Physical Review B 09/2013; 88:104401. · 3.77 Impact Factor
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    ABSTRACT: Structural refinement, lattice micro-strain and spontaneous strain analyses have been carried out on selected members of the La(Fe1-xRux)AsO system using high-resolution neutron and synchrotron powder diffraction data. The obtained results indicate that the character of the tetragonal to orthorhombic structural transition changes from first order for x = 0.10, possibly to tricritical for x = 0.20, up to second order for x = 0.30; for x ≥ 0.40 symmetry breaking is suppressed, even though a notable increase of the lattice micro-strain develops at low temperature. By combining structural findings with previous muon spin rotation data, a phase diagram of the La(Fe1-xRux)AsO system has been drawn. Long-range ordered magnetism occurs within the orthorhombic phase (x ≤ 0.30), whereas short-range magnetism appears to be confined within the lattice strained region of the tetragonal phase up to x < 0.60. Direct comparison between the magnetic and structural properties indicates that the magnetic transition is always associated with structural symmetry breaking, although confined to a local scale at high Ru contents.
    Journal of Physics Condensed Matter 09/2013; 25(39):395701. · 2.36 Impact Factor
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    ABSTRACT: Structural refinement, lattice microstrain and spontaneous strain analyses have been carried out and a phase diagram has been drawn.
    08/2013;
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    ABSTRACT: The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW-type material have been studied by temperature-dependent neutron powder diffraction, low-temperature magnetometry, and heat capacity measurements. RbMnPO4 represents a rare example of a weak ferromagnetic polar material, containing Mn(2+) ions with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K shows that the compound crystallizes in the chiral and polar monoclinic space group P21 (No. 4) with the unit cell parameters: a = 8.94635(9), b = 5.43415(5), and c = 9.10250(8) Å and β = 90.4209(6)°. A close inspection of the crystal structure of RbMnPO4 shows that this material presents two different types of zigzag chains running along the b axis. This is a unique feature among the zeolite-ABW-type materials exhibiting the P21 symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic structure characterized by the propagation vector k1 = 0, resulting in the magnetic symmetry P21'. The magnetic moments lie mostly along the b axis with the ferromagnetic component being in the ac plane. Due to the geometrical frustration present in this system, an intermediate phase appears within the temperature range 4.7-5.1 K characterized by the propagation vector k2 = (kx, 0, kz) with kx/kz ≈ 2. This ratio is reminiscent of the multiferroic phase of the orthorhombic RMnO3 phases (R = rare earth), suggesting that RbMnPO4 could present some multiferroic properties at low temperature. Our density functional calculations confirm the presence of magnetic frustration, which explains this intermediate incommensurate phase. Taking into account the strongest magnetic interactions, we are able to reproduce the magnetic structure observed experimentally at low temperature.
    Inorganic Chemistry 08/2013; · 4.59 Impact Factor
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    ABSTRACT: The nature of triclinic to orthorhombic phase transition, at which colossal negative thermal expansion is observed, and the magnetic ordering of Bi1−xLaxNiO3 have been investigated with neutron powder diffraction (NPD) and x-ray absorption spectroscopy techniques. The presence of a charge-transfer transition from (Bi/La)3+0.5Bi5+0.5Ni2+O3 to (Bi/La)3+Ni3+O3, accompanied by the simultaneous structural distortion, was confirmed. The NPD data also revealed that magnetic ordering is present only in the insulating triclinic phase. The metallic orthorhombic phase was found to be nonmagnetic down to 10 K.
    Physical Review B 07/2013; 88(1). · 3.77 Impact Factor
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    ABSTRACT: The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW type material have been studied by temperature-dependent neutron powder diffraction, low temperature magnetometry and heat capacity measurements. RbMnPO4 represents a rare example of a weak ferromagnetic polar material, containing Mn2+ ions with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K shows that the compound crystallizes in the chiral and polar monoclinic space group P21 (No. 4) with the unit-cell parameters: a = 8.94635(9) Å, b = 5.43415(5) Å, c = 9.10250(8) Å and β = 90.4209(6)°. A close inspection of the crystal structure of RbMnPO4 shows that this material presents two different types of zigzag chains running along the b axis. This is a unique feature among the zeolite-ABW type materials exhibiting the P21 symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic structure characterized by the propagation vector k1 = 0 resulting in the magnetic symmetry P21′. The magnetic moments lie mostly along the b axis with the ferromagnetic component being in the ac plane. Due to the geometrical frustration present in this system, an intermediate phase appears within the temperature range 4.7 – 5.1 K characterized by the propagation vector k2 = (kx, 0, kz) with kx/kz ~ 2. This ratio is reminiscent of the multiferroic phase of the orthorhombic RMnO3 phases (R = rare earth). This suggests that RbMnPO4 could present some multiferroic properties at low temperature. Our density functional calculations confirm the presence of magnetic frustration, which explains this intermediate incommensurate phase. Taking into account the strongest magnetic interactions, we are able to reproduce the magnetic structure observed experimentally at low temperature.
    Inorganic Chemistry 07/2013; · 4.59 Impact Factor
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    ABSTRACT: We have investigated the magnetic properties of slightly doped multiferroic TbMnO3 after application of a magnetic field. The study focused on compositions TbMn1−xAxO3 (x ≤ 0.1) with A = Ga, Sc, Co and Al. The replacement of Mn by Ga, Al or Sc proved to be isovalent while the addition of Co leads to a partial charge transfer as Mn3+ + Co3+ → Mn4+ + Co2+. The samples with 10% of non-magnetic doping, TbMn0.9Sc0.1O3, TbMn0.9Al0.1O3 and TbMn0.9Ga0.1O3, preserve the long range antiferromagnetic ordering of the Mn sublattice with, however, reduced transition temperatures compared to TbMnO3. New magnetic interactions in the Co-doped compound lead to the suppression of Mn ordering in TbMn0.9Co0.1O3. The application of an external magnetic field produces similar metamagnetic transitions in all TbMn0.9A0.1O3 compounds that are ascribed to the Tb-sublattice. Powder neutron diffraction was used to determine the changes in the magnetic structure with applied magnetic field revealing a strong increase of F- and C-type magnetic reflections in these compounds. These results are accounted for by the anisotropic response of the Tb sublattice to a magnetic field while the Mn sublattice remains unchanged.
    Solid State Sciences. 07/2013; 21:37–43.
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    ABSTRACT: We report on the synthesis and characterization of BiFe0.5Mn0.5O3, a potential type-I multiferroic compound displaying temperature-induced magnetization reversal. Bulk samples were obtained by means of solid-state reaction carried out under the application of hydrostatic pressure of 6 GPa at 1100◦C. The crystal structure is a highly distorted perovskite with no cation order on the B site, where, besides a complex scheme of tilt and rotations of the TM-O6 octahedra, large off-centering of the bismuth ions is detected. Below T1 = 420 K the compound undergoes a first weak ferromagnetic transition related to the ordering of iron-rich clusters. At lower temperatures (just below RT) a complex thermally activated mechanism induces at first an enhancement of the magnetization at T2 = 288 K, then a spontaneous reversal giving rise to a negative response. The complementary use of powder neutron diffraction, superconducting quantum interference device magnetometry, and Mo ̈ssbauer spectroscopy allowed us to propose as a possible interpretation of the overall magnetic behavior the presence of an uncompensated competitive coupling between nonequivalent clusters of weakly ferromagnetic interactions characterized by different critical temperatures and resultant magnetizations. http://link.aps.org/doi/10.1103/PhysRevB.88.014431
    Physical Review B 07/2013; 88(1):014431. · 3.77 Impact Factor
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    ABSTRACT: Rare earth (R) molybdate pyrochlores, R2Mo2O7, are of interest as frustrated magnets. Polycrystalline samples of Lu2Mo2O7−x prepared at 1600 °C display a coexistence of cubic pyrochlore phases. Rietveld fits to powder neutron diffraction data and chemical analyses show that the miscibility gap is between a stoichiometric x=0 and an oxygen-deficient x≈0.4 phase. Lu2Mo2O7 behaves as a spin glass material, with a divergence of field cooled and zero field cooled DC magnetic susceptibilities at a spin freezing temperature Tf=16 K, that varies with frequency in AC measurements following a Vogel–Fulcher law. Lu2Mo2O6.6 is more highly frustrated spin glass and has Tf=20 K.
    Journal of Solid State Chemistry 07/2013; 203:199–203. · 2.04 Impact Factor
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    ABSTRACT: The magnetoelectric properties of the TbMn1-xScxO3 series have been studied at low temperatures by means of heat capacity, magnetic measurements and impedance spectroscopy. TbMnO3 exhibits as expected three transitions upon lowering the temperature corresponding to the magnetic ordering of the two sublattices (Mn and Tb) and the ferroelectric transition. Ferroelectricity disappears with Sc dilution for x > 0.1 because the non-collinear magnetic arrangement is destroyed. The dilution of Mn with a non-magnetic ion is also detrimental to the magnetic ordering of both Mn and Tb sublattices. The system evolves to a magnetic glassy state for the intermediate compositions. Formal TbScO3 shows Sc-deficiency and long range magnetic ordering of Tb(3+) moments in the ab-plane brought by the direct interaction between Tb(3+) ions. This ordering is different from the one found in TbMnO3 due to the lack of magnetic coupling between Tb- and Mn-sublattices. A small substitution of Sc by Mn in TbScO3 destroys the Tb ordering giving rise to a magnetic glass behaviour. This effect is ascribed to the partial polarization of Tb sublattice by the paramagnetic Mn which competes with the direct Tb-Tb exchange.
    Journal of Physics Condensed Matter 04/2013; 25(19):195601. · 2.36 Impact Factor
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    ABSTRACT: The crystal and magnetic structures of 10 and 20 nm sized (La1-xCax)MnO3 (x = 0.37, 0.50, 0.75) have been investigated between 5 and 300 K by means of Rietveld refinement of neutron powder diffraction data, coupled with transmission electron microscope observation and magnetization measurements. TEM observation reveals that nanoparticles are strongly affected by strain fields, probably originating from surface pressure. Irrespective of the composition, charge and orbital orderings are suppressed and Fz and Cy spin orderings coexist at low temperature; Cy and Fz orderings likely occur within the strained regions of the nanoparticles and in the matrix respectively. Moreover Gz and Az orderings are sometimes observed, and are likely to be taking place at the border of the strained regions.
    Journal of Physics Condensed Matter 04/2013; 25(17):176003. · 2.36 Impact Factor
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    ABSTRACT: The crystal and magnetic structures of the (La0.63Ca0.37)(Mn1−xTMx)O3 compounds (x=0.00, 0.03, 0.08; TM=Cu2+, Ni2+) were investigated between 5 K and 300 K by means of dc magnetic measurements and neutron powder diffraction analysis followed by Rietveld refinement. Both substituting cations lead to a reduction of the long range ferromagnetic ordering temperature; ferromagnetism is strongly suppressed in the 8% Cu-substituted sample, where long- and short-range FM magnetic orders coexist together with short-range A-type AFM order. This particular feature can be related to the Jahn–Teller character of Cu2+, absent in Ni2+, and suggests the occurrence of a quantum critical point in the (La0.63Ca0.37)(Mn1−xCux)O3 system.
    Journal of Solid State Chemistry 04/2013; 200:128–135. · 2.04 Impact Factor
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    Anil Jain, S. M. Yusuf, S. S. Meena, Clemens Ritter
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    ABSTRACT: We report the structural and magnetic properties of rare-earth substituted spin-chain compounds Ca2.75R0.25Co2O6 (R = Dy and Lu). The Rietveld refinement of neutron and x-ray powder diffraction patterns confirms the single-phase formation of both compounds in the rhombohedral structure (space group R[`3]c). The derived values (from the analysis of the neutron diffraction patterns at 50 K) of the bond-valence sum indicate a reduction in the oxidation state of the cobalt ions at the trigonal prism (TP) site (6a) with R substitution, which is further supported by low temperature neutron diffraction [where a zero value of the ordered moment at the 6b site and a reduction in the values of the maximum ordered moment at the TP site have been observed] and dc magnetization studies. In the neutron diffraction patterns, additional Bragg peaks appear for both compounds below Néel temperature (TN) of ~ 16 K, indicating the onset of an antiferromagnetic ordering of cobalt spin chains on the triangular lattice. The magnetic structure corresponds to a spin density wave (SDW) structure [with a propagation vector k = {0, 0, 1.02}], having c axis as direction of both moment and modulation. For both compounds, the refined values of the ordered moment at the 18e, 6b, and 6a sites are ~ 0.03(2), 0.02(2), and 4.2 (2) mB, respectively. Unlike the parent compound Ca3Co2O6, no temperature dependence as well as no time dependence in the intensity of the strongest antiferromagnetic reflection (10 t), corresponding to the propagation vector k = {0, 0, 1.02}, has been observed down to 1.5 K confirming that the SDW structure is stabilized by the substitution with rare-earth ions. The stabilization of the SDW structure and the observed decrease in the values of TN could be due to a decrease in the value of positive FM intrachain exchange interaction J with the rare-earth substitution in a system with competing intrachain and interchain exchange interactions.
    Physical Review B 03/2013; 87(9):094411. · 3.77 Impact Factor

Publication Stats

3k Citations
929.25 Total Impact Points

Institutions

  • 1991–2014
    • Institut Laue-Langevin
      Grenoble, Rhône-Alpes, France
  • 2013
    • Oak Ridge National Laboratory
      • Quantum Condensed Matter Division
      Oak Ridge, FL, United States
    • European Synchrotron Radiation Facility
      Grenoble, Rhône-Alpes, France
    • Università degli studi di Parma
      • Department of Chemistry
      Parma, Emilia-Romagna, Italy
    • University of Oxford
      • Inorganic Chemistry Laboratory
      Oxford, England, United Kingdom
  • 1995–2013
    • University of Zaragoza
      • • Departamento de Física de la Materia Condensada
      • • Faculty of Sciences (CIENCIAS)
      Zaragoza, Aragon, Spain
  • 2011
    • National Research Council
      Roma, Latium, Italy
  • 2010
    • Lomonosov Moscow State University
      Moskva, Moscow, Russia
  • 2007
    • Spanish National Research Council
      • Institut de Ciència de Materials de Barcelona
      Madrid, Madrid, Spain
  • 2006
    • Bhabha Atomic Research Centre
      • Solid State Physics Division
      Mumbai, State of Maharashtra, India
  • 2004
    • Durham University
      • Department of Chemistry
      Durham, England, United Kingdom
  • 2002
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
  • 1997–2002
    • Leibniz Institute for Solid State and Materials Research Dresden
      • Institute for Solid State Research
      Dresden, Saxony, Germany
  • 1999
    • Autonomous University of Barcelona
      • Institut de Ciència de Materials de Barcelona
      Cerdanyola del Vallès, Catalonia, Spain
  • 1992
    • University of Reading
      Reading, England, United Kingdom