Large Perpendicular Magnetic Anisotropy Induced by an Intersite Charge Transfer in Strained EuVO2H Films.

Perovskite oxides ABO3 continue to be a major focus in materials science. Of particular interest is the interplay between A and B cations as exemplified by intersite charge transfer (ICT), which causes novel phenomena including negative thermal expansion and metal-insulator transition. However, the ICT properties were achieved and optimized by cationic substitution or ordering. Here we demonstrate an anionic approach to induce ICT using an oxyhydride perovskite, EuVO2H, which has alternating layers of EuH and VO2. A bulk EuVO2H behaves as a ferromagnetic insulator with a relatively high transition temperature (TC) of 10 K. However, the application of external pressure to the EuIIVIIIO2H bulk or compressive strain from the substrate in the thin films induces ICT from the EuIIH layer to the VIIIO2 layer due to the extended empty V dxy orbital. The ICT phenomenon causes the VO2 layer to become conductive, leading to an increase in TC that is dependent on the number of carriers in the dxy orbitals (up to a factor of 4 for 10 nm thin films). In addition, a large perpendicular magnetic anisotropy appears with the ICT for the films of <100 nm, which is unprecedented in materials with orbital-free Eu2+, opening new perspectives for applications. The present results provide opportunities for the acquisition of novel functions by alternating transition metal/rare earth layers with heteroanions.

Large Magnetoelectric Coupling Near Room Temperature in Synthetic Melanostibite Mn2 FeSbO6.

Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn2 FeSbO6 (R3‾ space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature.

Double Double Cation Order in the High-Pressure Perovskites MnRMnSbO6.

Cation ordering in ABO3 perovskites adds to their chemical variety and can lead to properties such as ferrimagnetism and magnetoresistance in Sr2 FeMoO6 . Through high-pressure and high-temperature synthesis, a new type of "double double perovskite" structure has been discovered in the family MnRMnSbO6 (R=La, Pr, Nd, Sm). This tetragonal structure has a 1:1 order of cations on both A and B sites, with A-site Mn(2+) and R(3+) cations ordered in columns and Mn(2+) and Sb(5+) having rock salt order on the B sites. The MnRMnSbO6 double double perovskites are ferrimagnetic at low temperatures with additional spin-reorientation transitions. The ordering direction of ferrimagnetic Mn spins in MnNdMnSbO6 changes from parallel to [001] below TC =76 K to perpendicular below the reorientation transition at 42 K at which Nd moments also order. Smaller rare earths lead to conventional monoclinic double perovskites (MnR)MnSbO6 for Eu and Gd.

Unusual magnetic behaviors and electronic configurations driven by diverse Co(II) or Mn(II) MOF architectures.

Five novel metal organic frameworks were obtained by hydro-solvothermal reactions using the hexafluorisopropylidenebis(benzoic) acid (H2hfipbb) as linker and Co(II) or Mn(II) ions as connectors. [Co2(Hhfipbb)(TEA)], compound 1 (TEA = triethanolamine trianion) with a three-dimensional (3D) framework, and a tpu net; [Co1.5(hfipbb)2]·HN(CH2CH3)3 and [Co3(hfipbb)2]·2{HN(CH2CH3)3}, compounds 2 and 2-a, respectively, both with two-dimensional structure, sql topologies, and different layer packings. Compounds 3 and 4, having the general formula [M2(hfipbb)2]·C7H8, where M = Co (3) or Mn (4), have 3D frameworks with an sqc topology. A deep analysis of the magnetic measurements reveals different striking magnetic behaviors resulting from diverse secondary building unit and framework architectures. Compound 1 presents canted antiferromagnetic chains, compound 2 contains ferromagnetic linear trimeric clusters, and compound 3 exhibits ferromagnetic chains. For the three compounds, a 3D canted antiferromagnetic structure takes place at ∼8 K by means of weak magnetic interactions between the mentioned magnetic units. Such long-range magnetic order is precluded with the application of a high enough magnetic field. Compound 4 evidenced intrachain antiferromagnetic interactions.

Lithium storage mechanisms and effect of partial cobalt substitution in manganese carbonate electrodes.

A promising group of inorganic salts recently emerged for the negative electrode of advanced lithium-ion batteries. Manganese carbonate combines low weight and significant lithium storage properties. Electron paramagnetic resonance (EPR) and magnetic measurements are used to study the environment of manganese ions during cycling in lithium test cells. To observe reversible lithium storage into manganese carbonate, preparation by a reverse micelles method is used. The resulting nanostructuration favors a capacitive lithium storage mechanism in manganese carbonate with good rate performance. Partial substitution of cobalt by manganese improves cycling efficiency at high rates.

Synthesis and characterization of the ultramarine-type analog Na(8-x)[Si6Al6O24] x (S2,S3,CO3)(1-2).

The use of nitrite sodalite as a precursor to prepare new blue ultramarine analogs has been investigated. The encapsulation of the chromophores inside of beta cages was achieved by heating the nitrite sodalite precursor with a mixture of sodium carbonate, sulfur, and a reducing agent at about 1000 K under airtight conditions. The obtained new blue ultramarine-type material was characterized by means of X-ray and neutron powder diffraction, transmission electron microscopy, 29Si magic-angle-spinning NMR, IR, Raman, and diffuse reflectance spectroscopies. Thermogravimetric analysis and magnetic measurements were performed in order to determine water and chromophore contents, respectively. On the basis of the spectroscopic results and Rietveld analysis of neutron powder data, the beta cage filling was found to be yellow S2(-) and blue S3(-) chromophores along with carbonate anions. The determined chromophore concentration, about 0.31 mol per formula unit, is enough to have greenish-blue ultramarines, which proves that ultramarine analogs can be obtained from nitrite sodalite.

Mesoporous Silica Matrix as a Tool for Minimizing Dipolar Interactions in NiFe2O4 and ZnFe2O4 Nanoparticles.

NiFe2O4 and ZnFe2O4 nanoparticles have been prepared encased in the MCM (Mobile Composition of Matter) type matrix. Their magnetic behavior has been studied and compared with that corresponding to particles of the same composition and of a similar size (prepared and embedded in amorphous silica or as bare particles). This study has allowed elucidation of the role exerted by the matrix and interparticle interactions in the magnetic behavior of each ferrite system. Thus, very different superparamagnetic behavior has been found in ferrite particles of similar size depending on the surrounding media. Also, the obtained results clearly provide evidence of the vastly different magnetic behavior for each ferrite system.

Addressed realization of multication complex arrangements in metal-organic frameworks.

The preparation of materials with structures composed of multiple metal cations that occupy specific sites is challenging owing to the difficulty of simultaneously addressing the incorporation of different elements at desired precise positions. We report how it is possible to use a metal-organic framework (MOF) built with a rod-shaped inorganic secondary building unit (SBU) to combine multiple metal elements at specific positions in a manner that is controllable at atomic and mesoscopic scales. Through the combination of four different metal elements at judiciously selected molar ratios, 20 MOFs of different compositions and the same topology have been prepared and characterized. The use of diffraction techniques, supported by density functional theory calculations, has led us to determine various possible atomic arrangements of the metal cations within the SBUs. In addition, seven of the compounds combine multiple types of atomic arrangements, which are mesoscopically distributed along the crystals. Given the large diversity and importance of rod-based MOFs, we believe that these findings offer a new general strategy to produce complex materials with required compositions and controllable arrangements of the metal cations for desired applications.

Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide.

The perovskite polymorph of Mn(2)CrSbO(6) 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 ß = 90.36(1)°. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn(2+) and Cr(3+) sublattices below TN = 55 K 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 = [1/2 0 1/2]. 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 R3[combining macron] 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 = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to κ = [00 0.54] at about 10 K.

Synthesis, characterization and theoretical calculations of Cu(I) complex of trithiocyanuric acid [Cu(ttc)3] / Síntesis, caracterización y cálculos teóricos del complejo Cu(I) de ácido cianúrico [Cu(ttc)3] / Síntese, caracterização e cálculos teóricos do complexo Cu(I) de ácido cianúrico [Cu(ttc)3]

Abstract A new Cu(I) complex constructed by reaction of trithiocyanuric acid (ttc) and copper(II) perchlorate hexahydrate has been successfully synthesized by a slow sedimentation method in a DMF solvent at room temperature. The molecular structure of the compound was elucidated by MALDI-TOF MS, UV-Vis and FTIR spectroscopy, DSC-TGA analysis and magnetic susceptibility measurement. The proposed structure was corroborated by a computational study carried out with the Gaussian09® and AIMAII® programs using the RB3LYP hybrid DFT functional with both 6-31G and Alhrich-TZV basis sets. The calculated vibrational frequencies values were compared with experimental FTIR values. Photophysical properties of the synthesized complex were evaluated by UV-Visible spectroscopy and compared with computed vertical excitation obtained from TDDFT. The theoretical vibrational frequencies and the UV-Vis spectra are in good agreement with the experimental values. Additionally, the Frontier Molecular Orbitals (HOMO - LUMO) and the Molecular Electrostatic Potential of the complex was calculated using same theoretical approximation. The results showed the interaction between three coordinated ligand atoms and the Cu(I) ion.

Resumen Un nuevo complejo de Cu(I) elaborado por la reacción de ácido cianúrico (ttc) y perclorato de cobre(II) hexahidrato se sintetizó exitosamente por medio de un método lento de sedimentación en un solvente de DMF a temperatura ambiente. La estructura molecular del compuesto se determinó utilizando MS de MALDI-TOF, la espectroscopia de UV-VIS y de FTIR, el análisis de DSC-TGA y el análisis magnético de susceptibilidad. La estructura propuesta se corroboró por medio de un estudio computacional usando los programas Gaussian09® y AIMAII®, utilizando el híbrido RB3LYP DFT con los equipos 6-31G y Alhrich-TZV. Se compararon los valores calculados de las frecuencias vibracionales con los valores experimentales de FTIR. Se evaluaron las características fotofísicas del complejo sintetizado usando espectroscopia UV-visible y se compararon con la vibración vertical obtenida de TDDFT. Las frecuencias teóricas vibracionales y los espectros UV-VIS coinciden con los valores experimentales. Además, se calcularon las órbitas moleculares (HOMO - LUMO) y el potencial electrostático molecular del complejo usando la misma aproximación teórica. Los resultados demostraron la interacción entre tres receptores de átomos coordinados y el ion del Cu(I).

Resumo Um novo complexo de Cu(I) elaborado pela reação de ácido cianúrico (ttc) e perclorato de cobre (II) hexahidratado foi sintetizado de maneira exitosa por meio de um método lento de sedimentação em um solvente de DMF a temperatura ambiente. A estrutura molecular do composto se determinou utilizando MALDI-TOF, espectroscopia de UV-VIS e FTIR, DSC-TGA e análise magnético de susceptibilidade. A estrutura proposta se corroborou por meio de um estudo computacional usando os programas Gaussian09® e AIMAII®, utilizando o híbrido RB3LYP DFT com os equipamentos 6-31G e Alhirich-TZV. Se compararam os valores calculados das frequências vibracionais com os valores experimentais de FTIR. Se avaliaram as características fotofísicas do complexo sintetizado utilizando espectroscopia UV-VIS e se compararam com a vibração vertical obtida de TDDFT. As frequências teóricas vibracionais e os espectros UV-VIS coincidem com os valores experimentais. Além disso, se calcularam as órbitas moleculares (HOMO - LUMO) e o potencial eletrostático molecular do complexo utilizando a mesma aproximação teórica. Os resultados demonstraram a interação entre três receptores de átomos coordenados e o íon de Cu(I).