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We have investigated the electronic structure of the high oxidation state material YCrO4 within the framework of the Zaanen-Sawatzky-Allen phase diagram. While Cr4+-based compounds such as SrCrO3/CaCrO3 and CrO2 can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that YCrO4 is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band-structure calculations that the tetrahedral coordination of the Cr5+ ions in YCrO4 plays a decisive role, namely to diminish the bonding of the Cr 3d states with the top of the O 2p valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions. [ABSTRACT FROM AUTHOR]

A recent high-pressure study on barium Chromate BaCr04 reported a phase transition but the structure of the high-pressure phase structure could not be identified. This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of Aß04-type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as the quasihydrostatic pressure medium and density-functional theory calculations. Our studies allow us to identify the high-pressure phase as the P212121 post-barite-type phase, recently reported for BaS04. The equations of state of both, the low- and the high-pressure phases have been determined. Elastic constants of the initial barite-type phase were calculated and the shear and Young moduli, and the Poisson coefficient deduced from them. Finally Raman and infrared-active modes are also calculated, discussed, and compared with experiments when possible. As a first approximation, the vibrations can be separated in internal vibrations of the Cr04 tetrahedra and vibrations where the tetrahedral units behave as rigid units. Pressure coefficients of the different modes are reported being two soft modes found for the high-pressure phase. [ABSTRACT FROM AUTHOR]

Abstract: We have performed an investigation of the structural, microstructural and magnetic properties of the new compound IrSr2GdCu2O8. The sample was prepared under high temperature (∼1393K) and high-pressure conditions (∼60Kbars) in a Belt type apparatus. X-ray diffraction (XRD) analysis shows that this irido-cuprate is isostructural with the corresponding Ru-1212 phase. Structurally, this material shows an interesting hierarchy of ordering phenomena, whose observation actually depends on the technique used to analyze the material: from a “simple” cell a p×a p×3a p which is supported by XRD, through a “diagonal” one, as seen by SAED, to a microdomain texture of this last one cell supported by HREM. A ferrimagnetic IrIV–GdIII spin ordering is observed below 15K. The iridium oxidation state seems to be +4. [Copyright &y& Elsevier]

Abstract: Three-dimensional neutron depolarization experiments have been performed on RCrO4 (R=Y, Er, Tm, Yb) powder samples in order to gain insight into their magnetic domain structure in the submicrometer range. The temperature evolution of both the average domain size and the net magnetization of each compound has been studied for different applied magnetic fields. The largest average domain size at zero external magnetic field was found in YbCrO4. The effect of an applied magnetic field on the magnetic domain structure is relatively small in ErCrO4 and TmCrO4, when compared to YCrO4 and YbCrO4 where the average domain size even surpasses the average particle size determined by Scanning Electron Microscopy studies. [Copyright &y& Elsevier]

The coexistence of superconductivity and magnetic order seems to take place in the so called ruthenate-cuprates. Previous work has mainly focused on RuSr2GdCu2O8 where a magnetic transition is observed at 133 K and superconductivity has been claimed below Tc ∼46 K.At room pressure, Sm, Eu and Gd seem to be the only RE elements that accept to enter into the structure of RuSr2GdCu2O8. However high pressures and temperatures allows one to replace gadolinium by other lanthanide cations, although it is difficult to get pure samples.In order to better understand this, rather unusual behaviour, we have performed some substitutions in the title compound.The synthesis at high pressures (∼60 kbar) and high temperatures (∼1100 °C) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (Space group: P 4/ m m m) and the cell parameters linearly decrease following the lanthanide contraction.We have succeeded in replacing Gd by Tb, Dy, Y, Ho and Er, magnetic susceptibility measurements reveal the existence of interesting phenomena. The microstructure of these compounds has been studied by high-resolution electron microscopy.Also, at room pressure, we have replaced up to 10% calcium for strontium and observed that, in consonance with the difference in ionic radii, the unit cell contracts. On the other hand, the calcium-doped sample shows a positive magnetic susceptibility at 5 K. [Copyright &y& Elsevier]

Perovskite oxides AB O 3 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, EuVO 2 H, which has alternating layers of EuH and VO 2 . A bulk EuVO 2 H behaves as a ferromagnetic insulator with a relatively high transition temperature ( T C ) of 10 K. However, the application of external pressure to the Eu II V III O 2 H bulk or compressive strain from the substrate in the thin films induces ICT from the Eu II H layer to the V III O 2 layer due to the extended empty V d xy orbital. The ICT phenomenon causes the VO 2 layer to become conductive, leading to an increase in T C that is dependent on the number of carriers in the d xy 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 Eu 2+ , 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.

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., Competing Interests: The authors declare no conflict of interest.