Magnetic Interactions in the Double Perovskites R2NiMnO6 (R = Tb, Ho, Er, Tm) Investigated by Neutron Diffraction.

R2NiMnO6 (R = Tb, Ho, Er, Tm) perovskites have been prepared by soft-chemistry techniques followed by high oxygen-pressure treatments; they have been investigated by X-ray diffraction, neutron powder diffraction (NPD), and magnetic measurements. In all cases the crystal structure is defined in the monoclinic P21/n space group, with an almost complete order between Ni(2+) and Mn(4+) cations in the octahedral perovskite sublattice. The low temperature NPD data and the macroscopic magnetic measurements indicate that all the compounds are ferrimagnetic, with a net magnetic moment different from zero and a distinct alignment of Ni and Mn spins depending on the nature of the rare-earth cation.

Phonons and hybrid modes in the high and low temperature far infrared dynamics of hexagonal TmMnO3.

We report on temperature dependent TmMnO3 far infrared emissivity and reflectivity spectra from 1910 K to 4 K. At the highest temperature the number of infrared bands is lower than that predicted for centrosymmetric P63/mmc (D(4)(6h)) (Z = 2) space group due to high temperature anharmonicity and possible defect induced bitetrahedra misalignments. On cooling, at ~1600 ± 40 K, TmMnO3 goes from non-polar to an antiferroelectric-ferroelectric polar phase reaching the ferroelectric onset at ~700 K.

Crystal structure, phase transitions, and magnetic properties of iridium perovskites Sr2MIrO6 (M = Ni, Zn).

Double perovskites containing Ir(6+)/Ir(5+) with formula Sr2MIrO6 (M = Ni, Zn) have been synthesized under high oxygen pressure conditions. Their crystal structures have been studied by X-ray and neutron powder diffraction at room temperature (RT) and 2 K. At RT, these oxides crystallize in the monoclinic space group P2(1)/n with unit-cell parameters a ≈ √2a0, b ≈ √2a0, and c ≈ 2a0, and β ≈ 90°.

Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO₃.

We report on the far- and mid-infrared reflectivity of NdMnO3 from 4 to 300 K. Two main features are distinguished in the infrared spectra: active phonons in agreement with expectations for the orthorhombic [Formula: see text]-Pbnm (Z = 4) space group remaining constant down to 4 K and a well defined collective excitation in the THz region due to eg electrons in a d-orbital fluctuating environment. We trace its origin to the NdMnO3 high-temperature orbital disordered intermediate phase not being totally dynamically quenched at lower temperatures.

High temperature far-infrared dynamics of orthorhombic NdMnO3: emissivity and reflectivity.

We report on near normal far- and mid-infrared emission and reflectivity of NdMnO3 perovskite from room temperature to sample decomposition above 1800 K. At 300 K the number of infrared active phonons is in close agreement with the 25 calculated for the orthorhombic D(2h)(16)-Pbnm (Z = 4) space group. Their number gradually decreases as we approach the temperature of orbital disorder at ~1023 K where the orthorhombic O' lower temperature cooperative phase coexists with the cubic orthorhombic O.

Influence of the Bi3+ electron lone pair in the evolution of the crystal and magnetic structure of La(1-x)Bi(x)Mn2O5 oxides.

La(1-x)Bi(x)Mn2O5 (x = 0, 0.2, 0.4, 0.

Ferromagnetic Cu-O-Cu coupling in CaCu3Sn4O12 probed by neutron diffraction.

The A-site ordered perovskite oxide with the formula CaCu(3)Sn(4)O(12) has been synthesized in polycrystalline form under moderate pressure conditions (3.5 GPa) in combination with high temperature (1000 °C). This oxide crystallizes in the cubic space group [Formula: see text] (no.

Correlation between the crystal structure and the Curie temperature in RCu3(Mn3Fe)O12 (R = rare-earth) complex perovskites.

New members of the family of complex-perovskite oxides with the formula RCu(3)(Mn(3)Fe)O(12) (R = Ce, Pr, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) have been synthesized and characterized. Polycrystalline samples have been prepared from citrate precursors treated under moderate pressure conditions (2-3.5 GPa) and 1000 °C in the presence of KClO(4) as an oxidizing agent.

Collective phase-like mode and the role of lattice distortions at TN ~TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi).

We report on electronic collective excitations in RMn(2)O(5) (R =Pr, Sm, Gd, Tb) showing condensation starting at and below ~T(N) ~T(C)~ 40-50 K. Their origin is understood as partial delocalized e(g) electron orbitals in the Jahn-Teller distortion of the pyramid dimer with strong hybridized Mn(3+)-O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at T(N)~T(C).

On the magnetic structure of PrMn2O5: a neutron diffraction study.

The long-range magnetic ordering of PrMn(2)O(5) has been studied on polycrystalline samples from neutron diffraction and specific heat measurements. The onset of antiferromagnetic ordering is observed at T(N) ≈ 25 K. In the temperature interval 18 K < T < 25 K the magnetic structure is defined by the propagation vector k(1) = (1/2,0,0).

Stabilization and study of SrFe(1-x)Mn(x)O2 oxides with infinite-layer structure.

A series of layered oxides of nominal composition SrFe(1-x)Mn(x)O(2) (x = 0, 0.1, 0.2, 0.

Magnetic and structural features of the NdNi(1 - x)Mn(x)O3 perovskite series investigated by neutron diffraction.

Selected members of the perovskite series NdNi(1 - x)Mn(x)O(3) (0 ≤ x ≤ 1) have been prepared by a soft chemistry technique, followed by thermal treatments either under high oxygen pressure (x ≤ 0.5) or in air (x > 0.5).

High-pressure synthesis and neutron diffraction investigation of the crystallographic and magnetic structure of TeNiO3 perovskite.

TeNiO(3) has been prepared under moderate pressure conditions (3.5 GPa), starting from a reactive TeO(2) and Ni(OH)(2) mixture contained in a sealed platinum capsule under the reaction conditions (850 °C for 2 h). The sample has been studied by neutron powder diffraction (NPD) data and magnetization measurements.

Magnetic and electronic properties of RNiO₃ (R = Pr, Nd, Eu, Ho and Y) perovskites studied by resonant soft x-ray magnetic powder diffraction.

Soft x-ray resonant magnetic powder diffraction of the ([Formula: see text]) reflection at the Ni L(2, 3) edges is used to study the magnetic and electronic properties of a series of RNiO(3) materials (with R = Pr, Nd, Eu, Ho and Y) below the metal-insulator transition. The polarization and energy dependence of the reflection gives further support for a non-collinear magnetic structure and charge disproportionation in the whole RNiO(3) series. Only small changes in the spectra of the magnetic ([Formula: see text]) reflection and in the absorption spectra could be detected.

Study of the valence state and electronic structure in Sr(2)FeMO(6) (M = W, Mo, Re and Sb) double perovskites.

The knowledge of the oxidation state of the transition metal cations in Sr(2)FeMO(6) (M = W, Mo, Re and Sb) double perovskites is of paramount importance to understand their appealing magnetoresistive or magnetic properties. We present a systematic investigation of the valences of Fe, W, Mo, Re and Sb cations in these perovskites using three different and complementary techniques of analysis. We have used a diffraction method, neutron powder diffraction (NPD), coupled with the bond-valence model; and two spectroscopy methods, X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS).

Enhancement of the Curie temperature along the perovskite series RCu3Mn4O12 driven by chemical pressure of R3+ cations (R = rare earths).

The compounds of the title series have been prepared from citrate precursors under moderate pressure conditions (P = 2 GPa) and 1000 degrees C in the presence of KClO(4) as oxidizing agent. The crystal structures are cubic, space group Im3 (No. 204); the unit cell parameters linearly vary from a = 7.

Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides.

An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure.

Evidence of kinetically arrested supercooled phases in the perovskite oxide NdNiO(3).

We report the time and temperature dependent response of thermopower in the non-magnetic perovskite oxide NdNiO(3). We find that on cooling below the metal-insulator transition temperature the system evolves into a phase separated state which consists of supercooled metallic and insulating phases. This phase separated state exhibits out of equilibrium features, such as cooling rate dependence and time dependence.

The role of the Pb2+ 6s lone pair in the structure of the double perovskite Pb2ScSbO6.

The new double perovskite Pb2ScSbO6 was synthesized by standard ceramic procedures; the Rietveld refinement of room temperature neutron powder diffraction data shows that the crystal structure is well defined in the space group Fm3[combining macron]m. It contains a completely ordered array of alternating ScO6 and SbO6 octahedra sharing corners; the PbO12 polyhedra present an off-center displacement of the lead atoms along the [111] direction, due to the electrostatic repulsion between the Pb2+ 6s lone pair and the Pb-O bonds of the cuboctahedron. Dielectric permittivity measurements show a peak near 343 K, with a Curie-Weiss response above this temperature, which suggests an antiferroelectric behavior.

High-pressure synthesis of the double perovskite Sr(2)FeMoO(6): increment of the cationic ordering and enhanced magnetic properties.

The double perovskite Sr(2)FeMoO(6) has been prepared in polycrystalline form by high-pressure methods, starting from a precursor developed via a citrate technique, containing an elevated degree of anti-site disordering. The application of high external pressure (2 GPa) to Sr(2)FeMoO(6) promotes the long distance Fe/Mo cationic order, due to the smaller lattice volume of the ordered sample. Both the disordered perovskite obtained at ambient pressure and the sample synthesized under high-pressure methods have been characterized by means of x-ray diffraction, neutron powder diffraction and magnetic measurements.

Slow dynamics in hard condensed matter: a case study of the phase separating system NdNiO(3).

We report the time dependent response of electrical resistivity in the non-magnetic perovskite oxide NdNiO(3) in its phase separated state and provide a physical explanation of the observations. We also model the system and make an accurate Monte Carlo simulation of the observed behavior. While cooling, a phase separation takes place in the system below its metal-insulator transition temperature and in this state the material exhibits various dynamical phenomena such as relaxation of resistivity, dependence of resistivity on cooling rate and rejuvenation of the material after ageing.

On the evolution of the DyNiO3 perovskite across the metal-insulator transition though neutron diffraction and Mössbauer spectroscopy studies.

The structural changes of polycrystalline DyNiO3 perovskite across the metal-insulator transition (TMI = 564 K) have been studied by high resolution neutron diffraction techniques together with Mössbauer spectroscopy, in a sample doped with 1.5 at.% 57Fe.

Evolution of the crystal structure of RVO3 (R = La, Ce, Pr, Nd, Tb, Ho, Er, Tm, Yb, Lu, Y) perovskites from neutron powder diffraction data.

RVO3 perovskites have been prepared in the widest range of R (3+) ionic size, from LaVO3 to LuVO3. Pure polycrystalline samples have been obtained by a citrate technique leading to reactive RVO4 precursors, followed by thermal treatments in a reducing H2/N2 (15/85%) flow to stabilize V(3+) cations. These oxides have been studied at room temperature by high-resolution neutron powder diffraction to follow the evolution of the crystal structures along the series.

High-pressure synthesis and study of the crystal and magnetic structure of the distorted SeNiO3 and SeMnO3 perovskites.

We describe the preparation of SeMO(3) (M = Ni, Mn) under high pressure conditions (3.5 GPa), starting from reactive H(2)SeO(3) and MO mixtures, contained in sealed gold capsules under the reaction conditions 850 degrees C for 1 h. The polycrystalline samples have been studied by neutron powder diffraction (NPD) data and magnetization measurements.

Preparation and topotactical oxidation of ScVO3 with bixbyte structure: a low-temperature route to stabilize the new defect fluorite ScVO(3.5) metastable phase.

ScVO3 has been prepared by controlled reduction of a ScVO4 precursor under an H2/N2 flow at 1250 degrees C. The crystal structure of this material has been studied at room temperature by Rietveld refinement of high-resolution neutron powder diffraction (NPD) data. Sc3+ and V3+ are distributed at random over the metal sites of a C-M2O3 bixbyite-type structure, space group Ia3, a = 9.