Interplay between transition-metal K-edge XMCD, slight structural distortions and magnetism in a series of trimetallic (CoNi)[Fe(CN)] Prussian blue analogues.

The magnetic properties of a series of trimetallic (Co,Ni)Fe Prussian blue analogues (PBAs) were investigated by SQUID magnetometry and X-ray magnetic circular dichroism (XMCD) at the three transition metal (TM) K-edges. In turn, the PBA trimetallic series was used as a tool in order to better understand the information contained in TM K-edge XMCD and particularly the chemical nature of the probed species (extended sub-lattice or localized entities). The results show that the magnetic behavior of the compounds is dictated by competing exchange interactions between the Co-Fe and Ni-Fe pairs, without spin frustration.

Interplay between Transition-Metal K-edge XMCD and Magnetism in Prussian Blue Analogs.

To disentangle the information contained in transition-metal K-edge X-ray magnetic circular dichroism (XMCD), two series of Prussian blue analogs (PBAs) were investigated as model compounds. The number of 3d electrons and the magnetic orbitals have been varied on both sites of the bimetallic cyanide polymer by combining with the hexacyanoferrate or the hexacyanochromate entities' various divalent metal ions A (Mn, Fe, Co, Ni, and Cu). These PBA were studied by Fe and Cr X-ray absorption spectroscopy and XMCD.

Deciphering Photochemical Reaction Pathways of Aqueous Tetrachloroauric Acid by X-ray Transient Absorption Spectroscopy.

Photolysis reaction pathways of [Au(III)Cl] in aqueous solution have been investigated by time-resolved X-ray absorption spectroscopy. Ultraviolet excitation directly breaks the Au-Cl bond in [Au(III)Cl] to form [Au(II)Cl] that becomes highly reactive within 79 ps. Disproportionation of [Au(II)Cl] generates [Au(I)Cl], which is stable for ≤10 μs.

Toward Quantitative Magnetic Information from Transition Metal K-Edge XMCD of Prussian Blue Analogs.

Two series of Prussian blue analogs (PBA) were used as model compounds in order to disentangle the information contained in X-ray magnetic circular dichroism (XMCD) at the K-edges of transition metals. The number of 3d electrons on one site of the bimetallic cyanide polymer has been varied by associating to the [Fe(CN)] or the [Cr(CN)] precursors various divalent metal ions A (Mn, Fe, Co, Ni, and Cu). The compounds were studied by X-ray diffraction and SQUID magnetometry, as well as by X-ray absorption spectroscopy and XMCD at the K-edges of the A transition metal ion.

A cookbook for the investigation of coordination polymers by transition metal K-edge XMCD.

In order to disentangle the physical effects at the origin of transition metal K-edge X-ray magnetic circular dichroism (XMCD) in coordination polymers and quantify small structural distortions from the intensity of these signals, a systematic investigation of Prussian blue analogs as model compounds is being conducted. Here the effects of the temperature and of the external magnetic field are tackled; none of these external parameters modify the shape of the XMCD signal but they both critically modify its intensity. The optimized experimental conditions, as well as a reliable and robust normalization procedure, could thus be determined for the study of the intrinsic parameters.

Os Doping Suppressed Cu-Fe Charge Transfer and Induced Structural and Magnetic Phase Transitions in LaCuFeOsO ( = 1 and 2).

B-site Os-doped quadruple perovskite oxides LaCuFeOsO ( = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCuFeO experiences Cu-Fe intermetallic charge transfer that changes the Cu/Fe charge combination to Cu/Fe at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os and mixed Os valence states are determined by X-ray absorption spectroscopy for = 1 and = 2 compositions, respectively.

Tricolor Ho^{3+} Photoluminescence Enhancement from Site Symmetry Breakdown in Pyrochlore Ho_{2}Sn_{2}O_{7} after Pressure Treatment.

The photoluminescence (PL) characterization spectrum has been widely used to study the electronic energy levels. Ho^{3+} is one of the commonly used doping elements to provide the PL with concentration limited to 1% atomic ratio. Here, we present a tricolor PL achieved in pyrochlore Ho_{2}Sn_{2}O_{7} through pressure treatment at room temperature, which makes a non-PL material to a strong multiband PL material with Ho^{3+} at the regular lattice site with 18.

A new internally heated diamond anvil cell system for time-resolved optical and x-ray measurements.

We have developed a new internally heated diamond anvil cell (DAC) system for in situ high-pressure and high-temperature x-ray and optical experiments. We have adopted a self-heating W/Re gasket design allowing for both sample confinement and heating. This solution has been seldom used in the past but proved to be very efficient to reduce the size of the heating spot near the sample region, improving heating and cooling rates as compared to other resistive heating strategies.

Sequential Spin State Transition and Intermetallic Charge Transfer in PbCoO.

Spin state transitions and intermetallic charge transfers can essentially change material structural and physical properties while excluding external chemical doping. However, these two effects have rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO with a simple ABO composition under high pressure.

Near-Room-Temperature Ferrimagnetic Ordering in a B-Site-Disordered 3d-5d-Hybridized Quadruple Perovskite Oxide, CaCuMnOsO.

A new 3d-5d hybridization oxide, CaCuMnOsO (CCMOO), was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes to an A-site-ordered but B-site-disordered quadruple perovskite structure with a space group of 3̅ (No. 204).

Epsilon iron as a spin-smectic state.

Using X-ray emission spectroscopy, we find appreciable local magnetic moments until 30 GPa to 40 GPa in the high-pressure phase of iron; however, no magnetic order is detected with neutron powder diffraction down to 1.8 K, contrary to previous predictions. Our first-principles calculations reveal a "spin-smectic" state lower in energy than previous results.

SrFeReO double perovskites: magnetoresistance and (magneto)thermopower.

Polycrystalline Sr2Fe1+xRe1-xO6 samples have been synthesized and structurally characterized by X-ray powder diffraction, transmission electron microscopy and X-ray absorption spectroscopy. Resistivity strongly increases with x, but a large and negative magnetoresistance persists up to x = 0.33.

High-Temperature Ferrimagnetic Half Metallicity with Wide Spin-up Energy Gap in NaCuFeOsO.

A new oxide NaCuFeOsO is synthesized using high pressure and temperature conditions. The Rietveld structural analysis shows that the compound possesses both A- and B-site ordered quadruple perovskite structure in Pn3̅ symmetry. The valence states of transition metals are confirmed to be Cu/Fe/Os.

Tuning the Kondo resonance in two-dimensional lattices of cerium molecular complexes.

Cerium intermetallics have raised a lot of interest for the past forty years thanks to their very unusual and interesting electronic and magnetic properties. This can be explained by the peculiar electronic configuration of Ce (4f1) that allows different oxidation states leading to singular behavior such as quantum phase transitions, heavy-fermion behavior and the Kondo effect. In this work, we used a mixed-valence molecular analogue to study the Kondo effect down to the atomic scale by means of scanning tunneling microscopy/spectroscopy (STM/STS) for which new many-body effects are expected to emerge due to reduced dimensionality and specific chemical environment of the 4f-ion.

High-Pressure Synthesis and Ferrimagnetic Ordering of the B-Site-Ordered Cubic Perovskite PbFeOsO.

PbFeOsO was prepared for the first time by using high-pressure and high-temperature synthesis techniques. This compound crystallizes into a B-site-ordered double-perovskite structure with cubic symmetry Fm3̅m, where the Fe and Os atoms are orderly distributed with a rock-salt-type manner. Structure refinement shows an Fe-Os antisite occupancy of about 16.

Microsecond time-resolved energy-dispersive EXAFS measurement and its application to film the thermolysis of (NH₄)₂[PtCl₆].

Microsecond (μs) time-resolved extended X-ray absorption fine structure spectroscopy (EXAFS) has been developed using an energy-dispersive EXAFS (EDE) setup equipped with a silicon Quantum Detector ULTRA. The feasibility was investigated with a prototypical thermally driven redox reaction, the thermal decomposition of (NH₄)₂[PtCl₆]. EXAFS data were collected with snapshots every 60 μs during the course of the thermolysis reaction, then averaged for 100 times along the reaction to get better signal to noise ratio which reduces the time resolution to 6 millisecond (ms).

Room-temperature photoinduced electron transfer in a Prussian blue analogue under hydrostatic pressure.

In from the cold: The Co(III)Fe(II) state of a CoFe Prussian blue analogue undergoes a Co(III)-Fe(II) →(Co(II)-Fe(III))* electron transfer at room temperature when irradiated by visible light (532 nm; see scheme). This property was confirmed using energy-dispersive X-ray absorption spectroscopy at the Co and Fe K-edges of the piezo-induced Co(III)Fe(II) state.

Influence of monomer feeding on a fast gold nanoparticles synthesis: time-resolved XANES and SAXS experiments.

A comprehensive study of the mechanism of gold nanoparticle formation has been conducted using third-generation synchrotrons. The particles were obained by reduction of AuCl(3) by BH(4)(-) in toluene. Gold oxidation state was monitored by X-ray absorption near edge spectroscopy (XANES), while the size and concentration of the nanoparticles were assessed by small-angle X-ray scattering (SAXS).

XMCD for monitoring exchange interactions. The role of the Gd 4f and 5d orbitals in metal-nitronyl nitroxide magnetic chains.

We report here the X-ray magnetic circular dichroism (XMCD) study at the Gd M(4,5)- and L(2,3)-edges of two linear magnetic chains involving Gd(III) cations bridged by nitronyl nitroxide radicals. This spectroscopy directly probes the magnetic moments of the 4f and 5d orbitals of the gadolinium ions. We compare macroscopic magnetic measurements and local XMCD signals.