Antiferromagnetic vs ferromagnetic interactions and spin-glass-like behavior in ruthenates

We have made a series of gradient-corrected relativistic full-potential density-functional calculation for Ca-substituted and hole-doped SrRuO$_3$ in para, ferro, and $A$-, $C$-, and $G$-type antiferromagnetic states. Magnetic phase-diagram data for Sr$_{1-x}$Ca$_x$RuO$_3$ at 0 K are presented. Neutron diffraction measurement combined with total energy calculations show that spin-glass behavior with short-range antiferromagnetic interactions rules in CaRuO$_3$. The substitution of Sr by Ca in SrRuO$_3$ decreases the ferromagnetic interaction and enhances the $G$-type antiferromagnetic interaction; the $G$-AF state is found to stabilize around $x$ = 0.75 consistent with experimental observations. Inclusion of spin-orbit coupling is found to be important in order to arrive at the correct magnetic ground state in ruthenates.Comment: 5 pages, 3 figures. Solid state communications (in press

Electronic Structure of the Complex Hydride NaAlH4

Density functional calculations of the electronic structure of the complex hydride NaAlH4 and the reference systems NaH and AlH3 are reported. We find a substantially ionic electronic structure for NaAlH4, which emphasizes the importance of solid state effects in this material. The relaxed hydrogen positions in NaAlH4 are in good agreement with recent experiment. The electronic structure of AlH3 is also ionic. Implications for the binding of complex hydrides are discussed.Comment: 4 pages, 5 figure

MgyNi1-y(Hx) thin films deposited by magnetron co-sputtering

In this work we have synthesised thin films of MgyNi1-y(Hx) metal and metal hydride with y between 0 and 1. The films are deposited by magnetron co-sputtering of metallic targets of Mg and Ni. Metallic MgyNi1-y films were deposited with pure Ar plasma while MgyNi1-yHx hydride films were deposited reactively with 30% H2 in the Ar plasma. The depositions were done with a fixed substrate carrier, producing films with a spatial gradient in the Mg and Ni composition. The combinatorial method of co-sputtering gives an insight into the phase diagram of MgyNi1-y and MgyNi1-yHx, and allows us to investigate structural, optical and electrical properties of the resulting alloys. Our results show that reactive sputtering gives direct deposition of metal hydride films, with high purity in the case of Mg~2NiH~4. We have observed limited oxidation after several months of exposure to ambient conditions. MgyNi1-y and MgyNi1-yHx films might be applied for optical control in smart windows, optical sensors and as a semiconducting material for photovoltaic solar cells

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Nanostructured Mgh2 Obtained By Cold Rolling Combined With Short-time High-energy Ball Milling

MgH2 was processed by short time high-energy ball milling (BM) and cold rolling (CR). A new alternative processing route (CR + BM) using the combination of CR followed by short time BM step was also applied. The effects on the final morphology, crystalline structure and H-sorption properties were evaluated. The CR + BM processing (compared to BM and CR process) resulted in an inhomogeneous particle size distribution and the biggest crystallite size of MgH2, showing that there is a clear dependence between the size/shape of the particles which compose the starting material and the efficiency of crystallite size reduction during the BM process. On the other hand, we observed that a short BM step improved the kinetic properties of the cold rolled material. It shows that the particle size reduction of MgH2 obtained by CR combined with the increase in specific surface area attained by short BM step could be key factors to allow the use of the CR + BM route.161158163Fu, Y., Kulenovic, R., Mertz, R., The cycle stability of mg-based nanostructured materials (2008) Journal of Alloys and Compounds, 464, pp. 374-376. , http://dx.doi.org/10.1016%2Fj.jallcom.2007.09129Hanada, N., Hirotoshi, E., Ichikawa, T., Akiba, E., Fujii, H., Sem and tem characterization of magnesium hydride catalyzed with ni nano-particle or nb2o5 (2008) Journal of Alloys and Compounds, 450, pp. 395-399. , http://dx.doi.org/10.1016%2Fj.jallcom.2006.10128Liang, G., Huot, J., Boily, S., Van Neste, A., Schulz, R., Catalytic effect of transition metals on hydrogen sorption in nanocrystalline ball milled mgh2 -Tm (tm = ti, v, mn, fe and ni) systems (1999) Journal of Alloys and Compounds, 292, pp. 247-259. , http://dx.doi.org/10.1016%2FS0925-8388%2899%2900442-9Barkhordarian, G., Klassen, T., Bormann, R., Fast hydrogen sorption kinetics of nanocrystalline mg using nb2o5 as catalyst (2003) Scripta Materialia, 49, pp. 213-217. , http://dx.doi.org/10.1016%2FS1359-6462%2803%2900259-8Yavari, A.R., LeMoulec, A., De Castro, F.R., Deledda, S., Friedrichs, O., Botta, W.J., Improvement in h-sorption kinetics of mgh2 powders by using fe nanoparticles generated by reactive fef3 addition (2005) Scripta Materialia, 52, pp. 719-724. , http://dx.doi.org/10.1016%2Fj.scriptamat.2004.12020Leiva, D.R., Jorge, A.M., Ishikawa, T.T., Huot, J., Fruchart, D., Miraglia, S., Nanoscale grain refinement and h-sorption properties of mgh2 processed by high-pressure torsion and other mechanical routes (2010) Advanced Engineering Materials, 12, pp. 786-792. , http://dx.doi.org/10.1002%2Fadem.201000030Skripnyuk, V., Rabkin, E., Estrin, Y., Lapovok, R., The effect of ball milling and equal channel angular pressing on hydrogen absorptiondesorption properties of mg-4.95 wt% zn-0.71 wt% zr (zk60) alloy (2004) Acta Materialia, 52, pp. 405-414. , http://dx.doi.org/10.1016%2Fj.actamat.2003.09.025Leiva, D.R., Floriano, R., Huot, J., Jorge, A.M., Bolfarini, C., Kiminami, C.S., Nanostructured mgh2 prepared by cold rolling and cold forging (2011) Journal of Alloys and Compounds, 509 (S), pp. 444-448. , http://dx.doi.org/10.1016%2Fj.jallcom.2011.01.097Huot, J., Nanocrystalline metal hydrides obtained by severe plastic deformations (2012) Metals, 2, pp. 22-40. , http://dx.doi.org/10.3390%2Fmet2010022Leiva, D.R., Huot, J., Ishikawa, T.T., Bolfarini, C., Kiminami, C.S., Jorge, A.M., Hydrogen activation behavior of commercial magnesium processed by different severe plastic deformation routes (2011) Materials Science Forum, 667-669, pp. 1047-1051. , http://dx.doi.org/10.4028%2Fwww.scientific.net%2FMSF.667-669.1047Lang, J., Huot, J., A new approach to the processing of metal hydrides (2011) Journal of alloys and compounds, 509, pp. L18-L22. , http://dx.doi.org/10.1016%2Fj.jallcom.2010.09.173Vincent, S.D., Lang, J., Huot, J., Addition of catalysts to magnesium hydride by means of cold rolling (2012) Journal of Alloys and Compounds, 512, pp. 290-295. , http://dx.doi.org/10.1016%2Fj.jallcom.2011.09.084Lu, L., Lai, M.O., (1998) Mechanical Alloying, , http://dx.doi.org/10.1016%2FS0921-5093%2898%2900676-5, Boston: KluwerReed-Hill, R.E., (1973) Physical Metallurgy and Principles, , 2nd ed. D. Van Nostrand CompanyGennari, F.C., Castro, F.J., Urretavizcaya, G., Hydrogen desorption behavior from magnesium hydrides synthesized by reactive mechanical alloying (2001) Journal of alloys and compounds, 321, pp. 46-53. , http://dx.doi.org/10.1016%2FS0925-8388%2800%2901460-2Varin, R.A., Czujko, T., Chiu, C., Wronski, Z.J., Particle size effects on the desorption properties of nanostructured magnesium dihydride (mgh2) synthesized by controlled reactive mechanical milling (crmm) (2006) Journal of Alloys and Compounds, 424, pp. 356-364. , http://dx.doi.org/10.1016%2Fj.jallcom.2005.12087Ln, A., (2008) Hydrogen Technology, , Berlin: Springer Verlagchapt. 16: Kinetics and ThermodynamicsImamura, H., Masanari, K., Kusuhara, M., Katsumoto, H., Sumi, T., Sakata, Y., High hydrogen storage capacity of nanosized magnesium synthesized by high energy ball-milling (2005) Journal of Alloys and Compounds, 386, pp. 211-216. , http://dx.doi.org/10.1016%2Fj.jallcom.2004.0414