C. Ritter

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

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Publications (435)1133.43 Total impact

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    ABSTRACT: The magnetic properties and magnetic structures of the R 5Ni2In4 and the microfibrous R 11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R 5Ni2In4 and R 11Ni4In9 compounds, respectively. As a result of the intra- and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings. A transition at T C = 125 K in Tb5Ni2In4 [κ 1 = (0, 0, 0)] leads to a ferro/ferrimagnetic order where the magnetic ordering in one of the three R-sublattices leads to the ordering of another one; the third sublattice stays non-magnetic. New magnetic Bragg peaks appearing below T N = 20 K can be indexed with the incommensurate magnetic propagation vector κ 2 = (0, 0.636, ½); at T N = 20 K a cycloidal spin order, which acts mostly upon the third R-sublattice, occurs. Ho5Ni2In4 establishes first antiferromagnetism [κ = (0, 0, 0)] at T N = 31 K on two R-sublattices; then the system becomes ferro/ferrimagnetic at T C = 25 K with the third sublattice ordering as well. Tb11Ni4In9 has three magnetic transitions at T C = 135 K, T N1 = 35 K and at T N2 = 20 K; they are respectively coupled to the appearance of different propagation vectors [κ 1 = (0, 0, 0), κ 2 = (0, 0, ½), κ 3 = (0, 1, ½)], which themselves are operating differently on the five different R-sublattices. Two sublattices remain mostly ferromagnetic down to lowest temperature while the three others are predominantly coupled antiferromagnetically. In Ho11Ni4In9 a purely antiferromagnetic order, described by four different magnetic propagation vectors [κ 1 = (0, 0.62, 0), κ 2 = (0, 1, 0), κ 3 = (0, 0, ½), κ 4 = (0, 1, ½)], succeedingly includes all five different sublattices on cooling through transitions at T N1 = 22 K, T N2 = 12 K, T N3 = 8 K and T N4 = 7 K. The strength of the magnetic interactions of the different sublattices can be linked to structural details for both R 5Ni2In4 and R 11Ni4In9 compounds.
    Journal of Physics Condensed Matter 11/2015; 27(47):476001. DOI:10.1088/0953-8984/27/47/476001 · 2.35 Impact Factor
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    ABSTRACT: We report measurements performed on a polycrystalline sample of the pyrochlore compound Nd2Sn2O7. It undergoes a second order magnetic phase transition at Tc ~ 0.91 K to a noncoplanar all-in-all-out magnetic structure of the Nd3+ magnetic moments. The thermal behavior of the low temperature specific heat fingerprints excitations with linear dispersion in a three-dimensional lattice. The temperature independent spin-lattice relaxation rate measured below Tc and the anomalously slow paramagnetic spin dynamics detected up to ~ 30 Tc are suggested to be due to magnetic short-range correlations in unidimensional spin clusters, i.e., spin loops. The observation of a spontaneous field in muon spin relaxation measurements is associated with the absence of a divergence-free field for the ground state of an all-in-all-out pyrochlore magnet as predicted recently.
    Physical Review B 10/2015; 92(14). DOI:10.1103/PhysRevB.92.144423 · 3.74 Impact Factor
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    ABSTRACT: Two new cation-ordered polymorphs of Mn2ScSbO6 have been synthesised at high-pressure. At 5.5 GPa and 1523 K Mn2ScSbO6 crystallizes in the Ni3TeO6-type structure with the polar R3 space group and cell parameters a = 5.3419 (5) Å and c = 14.0603 (2) Å. Below TC = 42.0 K it exhibits ferrimagnetic order with a net magnetization of 0.6μB arising from unusual site-selective Mn/Sc disorder and is thus a potential multiferroic material. A double perovskite phase obtained at 12 GPa and 1473 K crystallizes in the non-polar P21/n monoclinic space group with cell parameters a = 5.2909 (3) Å, b = 5.4698 (3) Å, c = 7.7349 (5) Å and β = 90.165 (6) °. Magnetization and neutron diffraction experiments reveal antiferromagnetic order below TN = 22.3 K with the spins lying in the ac plane.
    Dalton Transactions 10/2015; 44(47). DOI:10.1039/C5DT03445K · 4.20 Impact Factor
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    ABSTRACT: The opening of a spin gap in the orthorhombic compounds CeT2Al10 (T=RuandOs) is followed by antiferromagnetic ordering at TN=27 and 28.5 K, respectively, with a small ordered moment (0.29-0.34μB) along the c axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with La doping in Ce1-xLaxT2Al10 (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND), and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 and 10 meV in the 10% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 μB along the b axis in Ce0.9La0.1Ru2Al10, however a moment of 0.23 μB still along the c axis in Ce0.9La0.1Os2Al10. This contrasting behavior can be explained by a different degree of hybridization in CeRu2Al10 and CeOs2Al10, being stronger in the latter than in the former. Muon spin rotation (μSR) studies on Ce1-xLaxRu2Al10 (x=0, 0.3, 0.5, and 0.7), reveal the presence of coherent frequency oscillations indicating a long-range magnetically ordered ground state for x=0 to 0.5, but an almost temperature independent Kubo-Toyabe response between 45 mK and 4 K for x=0.7. We compare the results of the present investigations with those reported on the electron and hole doping in CeT2Al10.
    Physical Review B 09/2015; 92(9). DOI:10.1103/PhysRevB.92.094425 · 3.74 Impact Factor
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    ABSTRACT: The double perovskite Yb2CoMnO6 has been synthesized with an almost perfect checkerboard arrangement of Co2+ and Mn4+ cations in the B-sublattice of the perovskite cell. It presents an anomaly in the electric capacitance and a strong magneto-dielectric effect at about 40 K whose interplay with the microscopic magnetic behavior has been investigated by means of neutron diffraction, magnetization, pyroelectric, and relative dielectric permittivity measurements. We show that the onset of an E-type antiferromagnetic ordering of Co2+ and Mn4+ moments monitored by neutron diffraction provokes the noticeable jump of the relative dielectric permittivity (∼9%) at about 40 K. It is also shown that this jump can be totally suppressed by application of a magnetic field of μ0H = 5 T. Neutron experiments and magnetic measurements confirm that such a suppression leading to a significant magneto-dielectric effect is driven by a metamagnetic phase transition from the peculiar E-type ordering of 3d moments into a collinear ferromagnetic order. Pyroelectric current measurements do not show any spontaneous electric polarization, so the large dielectric anomaly at zero field cannot be ascribed to a ferroelectric ordering.
    Applied Physics Letters 07/2015; 107(1). DOI:10.1063/1.4926403 · 3.30 Impact Factor
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    ABSTRACT: We investigated moderate temperature oxygen diffusion mechanisms in Sr2ScGaO5 with Brownmillerite structure type. From oxygen isotope 18O/16O exchange experiments we determined that oxygen mobility sets in above 550°C. Temperature dependent neutron and X-ray (synchrotron) diffraction experiments allowed to correlate the oxygen mobility with a subtle phase transition of the orthorhombic room temperature structure with I2mb space group towards Imma, going along with a disorder of the (GaO4)∞-tetrahedral chains. From lattice dynamical simulations we could clearly evidence that dynamic switching of the (GaO4)∞-tetrahedral chains from its R to L resonance form sets in at 600°C, thus correlating oxygen diffusion with the dynamic disorder. Oxygen ion diffusion pathways are thus constrained along the 1D-oxygen vacancy channels, which is a different diffusion mechanism compared to the isostructural CaFeO2.5, where diffusion of the apical oxygen atoms into the vacant lattice sites are equally involved in the diffusion pathway. The proposed ordered room temperature structure in I2mb is strongly supported by 17O, 45Sc, and 71Ga NMR measurements, which indicate the presence of crystallographically unique sites and the absence of local disordering effects below the phase transition. The electric field gradient tensor components measured at the nuclear sites are found in excellent agreement with calculated values using the WIEN2k programme. The oxygen site assignment has been independently confirmed by 17O{45Sc} transfer of adiabatic populations double resonance (TRAPDOR) experiments
    The Journal of Physical Chemistry C 04/2015; 119(21):150424121033008. DOI:10.1021/acs.jpcc.5b02173 · 4.77 Impact Factor
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    ABSTRACT: The magnetic structure of the mixed rare-earth system PrxY1-xFe3(BO3)4 has been studied by elastic neutron powder diffraction and magnetic measurements. A spin reorientation from easy axis to easy plane occurs in the concentration range x=0.67-0.45 through the formation of inclined magnetic structures. The inclination of the Fe moments from the basal plane depends on the Pr content and ranges from 67(2)° for x=0.67 to 16(4) for x=0.45 at T=3K. A nonmonotonic change of the inclination angle with temperature is found for all compounds but there is no sign of a spontaneous spin reorientation in the temperature range of magnetic order. An approach based on a crystal-field model for the Pr3+ ion and on the molecular-field approximation is used to describe the magnetic characteristics of the system PrxY1-xFe3(BO3)4. A good agreement between the experimental and calculated temperature dependences of the magnetic susceptibilities and the angle of inclination of Fe moments from the basal plane has been achieved.
    Physical Review B 04/2015; 91(13). DOI:10.1103/PhysRevB.91.134416 · 3.74 Impact Factor
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    ABSTRACT: The opening of a spin gap in the orthorhombic compounds CeT$_2$Al$_{10}$ (T = Ru and Os) is followed by antiferromagnetic ordering at $T_N$ = 27 K and 28.5 K, respectively, with a small ordered moment (0.29$-$0.34$\mu_B$) along the $c-$axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with 10\% La doping in Ce$_{1-x}$La$_x$T$_2$Al$_{10}$ (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND) and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 meV and 10 meV in the 10\% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 $\mu_B$ along the $b-$axis (moment direction changed compared with the undoped compound), in Ce$_{0.9}$La$_{0.1}$Ru$_2$Al$_{10}$, however a moment of 0.23 $\mu_B$ still along the $c-$axis in Ce$_{0.9}$La$_{0.1}$Os$_2$Al$_{10}$. This contrasting behavior can be explained by a different degree of hybridization in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$, being stronger in the latter than in the former. Muon spin rotation ($\mu$SR) studies on Ce$_{1-x}$La$_x$Ru$_2$Al$_{10}$ ($x$ = 0, 0.3, 0.5 and 0.7), reveal the presence of coherent frequency oscillations indicating a long$-$range magnetically ordered ground state for $x$ = 0 to 0.5, but an almost temperature independent Kubo$-$Toyabe response between 45 mK and 4 K for $x$ = 0.7. We will compare the results of the present investigations with those reported on the electron and hole$-$doping in CeT$_2$Al$_{10}$.
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    ABSTRACT: The perovskite polymorph of Mn2CrSbO6 compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P21/n space group with cell parameters a = 5.2180 (2) Å, b = 5.3710(2) Å, c = 7.5874(1) Å and β = 90.36(1)º. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn2+ and Cr3+ sublattices below TN = 55K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector κ = [½ 0 ½]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R-3 space group with cell parameters a = 5.2084 (4) Å and c = 14.4000 (11) Å. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with κ = [0 0 0.46] below 60 K, and the temperature dependence of the propagation vector up to κ = [0 0 0.54] at about 10 K.
    Dalton Transactions 01/2015; 44(23). DOI:10.1039/C4DT03849E · 4.20 Impact Factor
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    ABSTRACT: We report the rich magnetic behaviour of Sr2CoNb1-xTixO6 (0≤x≤0.5) oxides as a result of their complex microstructure. Although these oxides show an average simple-cubic perovskite structure, they present a flexible microstructure due to short-range ordering between Co/Ti and Nb cations in the perovskite B-sites. The microstructure consists of double-cubic perovskite domains grown in a simple-cubic perovskite matrix. The size and number of the double-cubic perovskite domains decrease as the Ti content increases. As a result of aliovalent substitution of Nb5+ by Ti4+ in the parent Sr2CoNbO6 mixed-valence Co3+/Co4+ oxides are obtained. A spin glass-like state has been observed at low temperatures for all the series, with freezing temperatures increasing with the Ti-content in the range 22 to 33 K. Furthermore, the x=0.3 and x=0.5 samples show non-interacting superparamagnetic particles-like dynamics, associated to relative high amounts Co4+, with “blocking temperatures” of 13 and ~16 K, respectively. The complex magnetic behaviour of the title oxides seems to be connected with the clustering of magnetic Co3+ and the distribution of Co4+ as a result of the microstructure.
    Dalton Transactions 01/2015; 44(8). DOI:10.1039/C4DT03112A · 4.20 Impact Factor
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    ABSTRACT: The magnetism of the A-site-ordered perovskite LaMn3V4O12 is studied comprehensively by means of neutron powder diffraction experiments and theoretical calculations. Magnetic neutron diffraction results show that a rhombohedral 60° spin structure emerges on the cubic lattice below a 44-K Néel transition. Ab initio electronic structure calculations confirm that high-spin Mn2+ moments are localized while V 3d-band states are itinerant, and that the noncollinear 60° spin structure is more stable than collinear ferromagnetic or G-type antiferromagnetic alternatives. Effective Heisenberg model calculations reveal that the appearance of such a nontrivial spin structure can be attributed to significant next-nearest-neighbor and third-nearest-neighbor magnetic interactions.
    Physical Review B 12/2014; 90(21). DOI:10.1103/PhysRevB.90.214405 · 3.74 Impact Factor
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    ABSTRACT: The low temperature properties of Pr0.50Sr0.50CoO3 are studied in comparison to Pr0.50Ca0.50CoO3, which is known to exhibit a Pr3+/Pr4+ valence shift below TMI~80 K. The evolution of the Pr-O network strongly differs in the Sr and Ca compounds, but both have in common a prominent and sudden contraction of some Pr-O bonds. The structural phase transition that accompanies the so-called magnetocrystalline anisotropy transition at TS~120 K in Pr0.50Sr0.50CoO3 brings about a notable contraction of some Pr-O2 bonds. The observations give support to the active participation of Pr-4f electrons at the intriguing magnetostructural transition (TS) in Pr0.50Sr0.50CoO3. In addition, we have confirmed that (in absence of praseodymium) the magnetostructural transition is suppressed in (Nd2/3La1/3)0.50Sr0.50CoO3, a perovskite with the same average cationic size at the A-site than Pr0.50Sr0.50CoO3.
    Physica B Condensed Matter 11/2014; 455. DOI:10.1016/j.physb.2014.07.045 · 1.32 Impact Factor
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    ABSTRACT: We present a detailed investigation of the hole (3\% Re) doping effect on the polycrystalline CeRu$_{2}$Al$_{10}$ sample by magnetization, heat capacity, resistivity, muon spin rotation ($\mu$SR), and neutron scattering (both elastic and inelastic) measurements. CeRu$_2$Al$_{10}$ is an exceptional cerium compound with an unusually high Neel temperature of 27 K. Here we study the stability of the unusual magnetic order by means of controlled doping, and we uncover further surprising attributes of this phase transition. The heat capacity, resistivity and $\mu$SR measurements reveal an onset of magnetic ordering below 23 K, while a broad peak at 31 K (i.e. above $T_N$), has been observed in the temperature dependent susceptibility, indicating an opening of a spin gap above $T_N$. Our important finding, from the neutron diffraction, is that the compound orders antiferromagnetically with a propagation vector $\bf k$ = (1 0 0) and the ordered state moment is 0.20(1)$\mu_B$ along the $b-$axis. This is in sharp contrast to the undoped compound, which shows AFM ordering at 27 K with the ordered moment of 0.39(3)$\mu_B$ along the $c-$axis. Similar to CeRu$_2$Al$_{10}$ our inelastic neutron scattering study on the Re doped shows a sharp spin gap-type excitation near 8 meV at 5 K, but with slightly reduced intensity compared to the undoped compound. Further the excitation broadens and shifts to lower energy ($\le$ 4 meV) near 35 K. These results suggest that the low temperature magnetic properties of the hole doped sample is governed by the competition between the anisotropic hybridization effect and crystal field anisotropy as observed in hole-doped CeOs$_2$Al$_{10}$.
    Physical review. B, Condensed matter 10/2014; 90(17):174412. DOI:10.1103/PhysRevB.90.174412 · 3.66 Impact Factor
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    ABSTRACT: The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing propagation vector κ= [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material encountering ferrielectric property and long period antiferromagnetic structure
    09/2014; 2(43). DOI:10.1039/C4TC01450B
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    ABSTRACT: We have studied the structural and physical properties of the La2-xTbxCoMnO6 series. The crystal and magnetic structures of these compounds were determined by x-ray and neutron diffraction techniques. All samples belong to the family of double perovskites with space group P21/n, but the Co/Mn ordering is not perfect, and antisite defects are formed. The concentration of these defects increases for intermediate compositions, indicating that La/Tb disorder influences the Co/Mn arrangement. A ferromagnetic ground state is established due to the strong Mn(4+)-O-Co(2+) superexchange interaction. For the intermediate compositions and at low temperature, the Co/Mn ordering is accompanied by the ordering of Tb(3+) moments in the ab-plane, indicating a mutual polarization between both sublattices. Macroscopic magnetic properties reveal that Curie temperature decreases as Tb content increases in correlation with the increase of the structural distortion. All samples show semiconducting behaviour, and overall the electrical resistivity increases with decreasing La-content. The dielectric constant (ε') has a value of around 12 at low temperatures for all samples, revealing the lack of permanent dipoles. The temperature dependence of ε' on warming exhibits a strong increase that depends heavily on the frequency of the electric field. This effect is ascribed to non-intrinsic effects such as contacts or internal barrier-layers.
    Journal of Physics Condensed Matter 09/2014; 26(38):386001. DOI:10.1088/0953-8984/26/38/386001 · 2.35 Impact Factor
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    ABSTRACT: Aliovalent substitution of Nb(5+) by Ti(4+) in Sr2LuNbO6 is limited to 10% of Nb atoms. A full structural determination by NPD confirms this and reveals that the structure is better described as a superstructure of the simple cubic perovskite (as previously reported) with the monoclinic cell 2(1/2)ap × 2(1/2)ap × 2ap and β ≈ 90° (S.G. P21/n). The substituted materials present both oxygen-vacancies induced by charge compensation and Sr-deficiency. Therefore, their formula should be given as Sr2-yLuNb1-xTixO6-δ. Electrical properties can be fully understood considering these compositional defects. The parent compound Sr2LuNbO6 presents low electrical conductivity in air, which improves by more than one order of magnitude upon Ti substitution. In any case, the title oxides show low electrical conductivity in a wide oxygen partial pressure (pO2) range (10(-25) atm ≤ pO2 ≤ 10(-1) atm). At high pO2 the conductivity increases with pO2 due to oxygen-vacancy annihilation and hole creation, according to a general p-type semiconducting mechanism; A-site substoichiometry and Ti-substitution are the origin of this behaviour. In the low pO2 region, the conductivity increases as the oxygen partial pressure decreases. Reduction of cations, Nb(5+) or Ti(4+), supports n-type conduction by electrons and oxygen vacancy creation. For the intermediate pO2 range a low ionic conduction contribution is observed. Although the estimated ionic conductivity is not high in the substituted compounds, the strategy seems to be valid since a significant enhancement of ionic conduction is observed upon aliovalent substitution.
    Dalton Transactions 08/2014; 43(37). DOI:10.1039/c4dt01337a · 4.20 Impact Factor
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    ABSTRACT: The synthesis of the new equiatomic RScSb (R = La-Nd, Sm, Gd-Tm, Lu, Y) compounds has been recently reported. These rare earth compounds crystallize in two different crystal structures, adopting the CeScSi-type (I4/mmm) for the lighter R (La-Nd, Sm) and the CeFeSi-type (P4/nmm) structure for the heavier R (R = Gd-Tm, Lu, Y). Here we report the results of neutron diffraction, magnetization and heat capacity measurements on some of these compounds (R = Ce, Pr, Nd, Gd and Tb). Band structure calculations have also been performed on CeScSb and GdScGe (CeScSi-type), and on GdScSb and TbScSb (CeFeSi-type) to compare and understand the exchange interactions in CeScSi and CeFeSi structure types. The neutron diffraction investigation shows that all five compounds order magnetically, with the highest transition temperature of 66 K in TbScSb and the lowest of about 9 K in CeScSb. The magnetic ground state is simple ferromagnetic (τ = [0 0 0]) in CeScSb, as well in NdScSb for 32 > T > 22 K. Below 22 K a second magnetic transition, with propagation vector τ = [¼ ¼ 0], appears in NdScSb. PrScSb has a magnetic structure within, determined by mostly ferromagnetic interactions and antiferromagnetic alignment of the Pr-sites connected through the I-centering (τ = [1 0 0]). A cycloidal spiral structure with a temperature dependent propagation vector τ = [δ δ ½] is found in TbScSb. The results of magnetization and heat capacity lend support to the main conclusions derived from neutron diffraction. As inferred from a sharp peak in magnetization, GdScSb orders antiferromagnetically at 56 K. First principles calculations show lateral shift of spin split bands towards lower energy from the Fermi level as the CeScSi-type structure changes to the CeFeSi-type structure. This rigid shift may force the system to transform from exchange split ferromagnetic state to the antiferromagnetic state in RScSb compounds (as seen for example in GdScSb and TbScSb) and is proposed to explain the change-over from a ferromagnetic structure as found in the CeScSi-type compounds CeScSb and NdScSb to the antiferromagnetic state as found in TbScSb and GdScSb.
    Journal of Physics Condensed Matter 08/2014; 26(36):366001. DOI:10.1088/0953-8984/26/36/366001 · 2.35 Impact Factor
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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.
    Journal of Applied Physics 04/2014; 115(17). DOI:10.1063/1.4865465 · 2.18 Impact Factor
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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). DOI:10.1107/S1600576714004907 · 3.72 Impact Factor
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    ABSTRACT: La2-xSrxCoTiO6 (0.6 <= x <= 1.0) compound series is prepared by Sr-substitution in the A-site of the perovskite by a modified Pechini procedure under air. Charge compensation as Sr2+ content increase occurs by Co2+ oxidation to Co3+. Reduced samples are obtained by further treatment under 5%H-2/Ar and characterized by Neutron Powder Diffraction. Upon redution, Co3+ to Co2+ reduction and oxygen vacancies creation are detected. Dependence of total conductivity with temperature and pO(2) exhibits a typical p-type semiconducting behaviour. Results show that the higher the Sr content, the higher holes (Co3+) concentration and consequently, La2-xSrxCoTiO6 (x = 1.0) shows the highest conductivity (13.23 S/cm at 1073 K in air). The negligible reactivity with YSZ, used as the electrolyte, of symmetrical cells under oxidant conditions and the moderate thermal expansion found by XRD point to their possible use as SOFC cathodes. Thus, La2-xSrxCoTiO6-based cathodes display polarization resistance of 0.9 Omega cm(2) at 1073 K in oxygen, only slightly above than the current state-of-the-art. Copyright
    International Journal of Hydrogen Energy 03/2014; 39(10):5440-5450. DOI:10.1016/j.ijhydene.2014.01.058 · 3.31 Impact Factor

Publication Stats

6k Citations
1,133.43 Total Impact Points


  • 1991-2015
    • Institut Laue-Langevin
      Grenoble, Rhône-Alpes, France
  • 2014
    • University Foundation San Pablo CEU
      • Faculty of Pharmacy
      Madrid, Madrid, Spain
  • 2013
    • European Synchrotron Radiation Facility
      • Division of Experiments
      Grenoble, Rhône-Alpes, France
    • Università degli studi di Parma
      • Department of Chemistry
      Parma, Emilia-Romagna, Italy
  • 1993-2013
    • University of Zaragoza
      • Department of Condensed Matter Physics
      Caesaraugusta, Aragon, Spain
  • 2011
    • Università degli Studi di Genova
      • Department of Chemistry and Industrial Chemistry
      Genova, Liguria, Italy
  • 2010
    • ETH Zurich
      Zürich, Zurich, Switzerland
    • University Joseph Fourier - Grenoble 1
      • Institut Néel
      Grenoble, Rhône-Alpes, France
    • Moscow State Forest University
      Mytishi, Moskovskaya, Russia
  • 2009
    • French National Centre for Scientific Research
      • Institut Néel
      Lutetia Parisorum, Île-de-France, France
    • University College London
      • Department of Chemistry
      Londinium, England, United Kingdom
  • 2008
    • Kyoto University
      • Division of Chemistry
      Kioto, Kyōto, Japan
  • 2007
    • Spanish National Research Council
      • Institut de Ciència de Materials de Barcelona
      Madrid, Madrid, Spain
  • 2004
    • Materials Science Institute of Barcelona
      Barcino, Catalonia, Spain
    • Durham University
      • Department of Chemistry
      Durham, England, United Kingdom
  • 1997-2002
    • Leibniz Institute for Solid State and Materials Research Dresden
      • Institute for Solid State Research
      Dresden, Saxony, Germany
    • University of Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 1992
    • University of Reading
      • Department of Chemistry
      Reading, England, United Kingdom