Magnetic and Electronic Properties of Eu₄Sr₄Ga₁₆Ge₃₀

Magnetization, static and ac magnetic susceptibility, nuclear forward scattering, and electrical resistivity measurements have been performed on polycrystalline Eu4Sr4Ga16Ge30, a type I clathrate that has divalent strontium and europium ions encapsulated within a Ga-Ge framework. These data are compared with those of type I clathrates Eu8Ga16Ge30 and Eu6Sr2Ga16Ge30. The ferromagnetic ordering of these Eu-containing clathrates is substantially altered by the incorporation of strontium, as compared to Eu8Ga16Ge30. Ferromagnetism, accompanied by a relatively large negative magnetoresistance, is observed below 15 and 20 K in Eu4Sr4Ga16Ge30 and Eu6Sr2Ga16Ge30, respectively. An effective magnetic moment of 7.83 µB per Eu ion is observed above 30 K for Eu4Sr4Ga16Ge30, a moment which is close to the free-ion moment of 7.94 µB per europium(II) ion

Development of a hard X-ray delay line for X-ray photon correlation spectroscopy and jitter-free pump–probe experiments at X-ray free-electron laser sources

A prototype device capable of splitting an X-ray pulse into two adjustable fractions, delaying one of them with the aim of performing split pulse X-ray photon correlation spectroscopy and pump–probe type studies was designed and manufactured. Time delays up to 2.95 ns have been demonstrated. The achieved contrast values of 56% indicate a feasibility of performing coherence-based experiments with the delay line

Interface-resolved study of magnetism in MgO/FeCoB/MgO trilayers using x-ray standing wave techniques

Interfaces in MgO/FeCoB/MgO trilayer have been studied with grazing incident nuclear resonance scattering using the x-ray standing wave technique. High depth selectivity of the present method allows one to measure magnetism and structure at the two interfaces of FeCoB, namely, FeCoB on MgO and MgO on FeCoB, independently, yielding an intriguing result that both interfaces are not symmetric. A high-density layer with an increased magnetic hyperfine field at the FeCoB-on-MgO interface suggests different growth mechanisms at the two interfaces. The azimuthal angle-dependent magneto-optic Kerr effect measurements reveal the presence of unusual uniaxial magnetic anisotropy (UMA) in the trilayer. An in situ temperature-dependent study discovered that this UMA systematically reduces with temperature. After annealing at 250∘C, the trilayer starts following the standard Stoner-Wohlfarth model for in-plane UMA. The trilayer becomes isotropic at 450∘C with an order-of-magnitude increase in coercivity. The asymmetry at the interfaces is in turn explained by boron diffusion from the FeCoB interface layer into the nearby MgO layer. Stress-induced UMA is observed in the boron-deficient FeCoB layer, superimposed with the bulk FeCoB layer, and found to be responsible for unusual UMA. The temperature-dependent variation in the UMA and coercivity can be understood in terms of variations in the internal stresses and coupling between FeCoB bulk and the interface layer

BaFe[CO3]2_{3}]_{2}, a new double carbonate: Synthesis, structural characterisation, and geostability implications for high and low PT

For the first time, a new ordered double carbonate, BaFe(CO$_3$)$_2$, was synthesized by a solid-state reaction between BaCO$_3$ and FeCO$_3$ at high pressure-temperature conditions (PT; 3 GPa and 700 °C). This finding adds a new so-far unknown member to the group of norsethite-structured carbonates, which is often used as a geochemical analogue for dolomite. Thermogravimetric (TG) analysis and differential scanning calorimetry (DSC) reveal that BaFe(CO$_3$)$_2$ decomposes between temperatures of 450 °C and 880 °C, which is similar to norsethite (BaMg(CO$_3$)$_2$), but substantially higher than of pure FeCO3. The formation of BaFe(CO$_3$)$_2$ through solid-state reaction is evidently slower than that of BaMg(CO$_3$)$_2$ and BaMn(CO$_3$)$_2$ under the same experimental conditions. Using synthetic BaFe(CO$_3$)$_2$ powder as starting material, the reaction in the presence of CO$_2$-bearing solution in contrast to water as a flux medium indicates the BaFe(CO$_3$)$_2$ instability at high PT conditions. The crystal structure and composition of the double carbonate were obtained using single crystal X-ray diffraction (XRD), Raman spectroscopy, and electron probe (EP) analysis. Two different types of the new double carbonate were identified: The experimentally derived phase belong to crystal structures that are related to the $R\bar{3}m$ and $R\bar{3}c$ space groups, respectively. The Raman spectra indicated that the difference is caused by a superstructure parallel to the c-axis. The charge and spin states of Fe in the new phases is determined using Nuclear forward scattering of synchrotron radiation. Furthermore, the thermodynamic properties of the double carbonate at standard conditions are estimated and a phase diagram is constructed depicting the stability field in low-temperature aqueous environments with these results being compared to natural aqueous solutions