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From the phase diagram proposed by Lei et al. [J. Appl. Phys. 101, 084105 (2007)JAPIAU0021-897910.1063/1.2715522], BaSn0.15Ti0.85O3 is chosen. It also exhibits a diffuse phase transition between cubic and rhombohedral (C-R) near room temperature. Dielectric analysis confirms a phase transition near room temperature (TC≈290 K). In addition, frequency dispersion in the dielectric constant, concomitantly, a loss peak is observed at low temperatures (T

Various exotic magnetic ground states have been anticipated in the higher transition metal (4d and 5d) oxides with large atomic spin-orbit coupling (SOC). However, many such expectations were not met because the exact atomic SOC strength and its consequent influence on electronic and magnetic ground states were always masked by solid-state effects. Here, we attempt to dope a dilute amount of Ir5+ (x=0.1-0.3) in place of Sb5+ in perfectly cubic Ba2YSbO6 with a target to minimize the effects of hopping between distant Ir ions and noncubic crystal field effect to promote the effect of SOC and to realize the coveted Jeff=0 ground state, expected for jj-coupled 5d4Ir5+ systems, purely from the consideration of atomic SOC. However, despite certain inhomogeneity in the distribution of the dopant Ir5+ ions in the system, our experimental results reveal high magnetic moments (away from the Jeff = 0 picture) with strong nearest-neighbor interaction, but without any long-range ordering, for the lowest doped system which continues to decrease with increasing Ir content, completely contrary to the expectation of the jj-coupling description. This observation strongly indicates that presence of a localized Ir moment, originating from L-S coupling interaction, might be the most appropriate mechanism here.

Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise `ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2$H$ spin-chain $d^4$ iridate Sr$_3$LiIrO$_6$ (SLIO) with geometric frustration. Our structural studies clearly reveal perfect Li-Ir chemical order in this compound. Our combined experimental and {\it ab-initio} electronic structure investigations establish a magnetic ground state with finite Ir$^{5+}$ magnetic moments in this compound, contrary to the anticipated nonmagnetic $J$=0 state. Furthermore, the dc magnetic susceptibility ($\chi$), heat capacity ($C_p$) and spin-polarized density functional theory (DFT) studies unravel that despite having noticeable antiferromagnetic correlation among the Ir$^{5+}$ local moments, this SLIO system evades any kind of magnetic ordering down to at least 2 K due to geometrical frustration, arising from the comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence promoting SLIO as a potential quantum spin liquid candidate., Comment: 13 pages, 5 figures. arXiv admin note: text overlap with arXiv:2107.04431

Spin-orbit coupling (SOC) often gives rise to interesting electronic and magnetic phases in an otherwise ordinary pool of paramagnetic heavy metal oxides. In presence of strong SOC, assumed to be working in $j$-$j$ coupling regime, 5$d^4$ iridates are generally speculated to possess a nonmagnetic $J_{eff}$~=~0 singlet ground state, which invariably gets masked due to different solid-state effects (e.g. hopping). Here, we try to probe the trueness of the atomic SOC-based proposal in an apparently 1-dimensional system, Sr$_3$NaIrO$_6$, possessing a 2$H$ hexagonal structure with well separated Ir$^{5+}$ (5$d^4$) ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of Sr$_3$NaIrO$_6$ is not nonmagnetic, rather accommodating a significantly high effective magnetic moment on Ir$^{5+}$ ion. However our combined dc susceptibility ($\chi$), ${}^{23}$Na nuclear magnetic resonance (NMR), muon-spin-relaxation/rotation ($\mu$SR) and heat capacity ($C_p$) measurements clearly refute any sign of spin-freezing or ordered magnetism among the Ir$^{5+}$ moments due to geometrical exchange frustration, while in-depth zero-field (ZF) and longitudinal field (LF) $\mu$SR investigations strongly point towards inhomogeneous quantum spin-orbital liquid (QSOL)-like ground state. In addition, the linear temperature dependence of both the NMR spin-lattice relaxation rate and the magnetic heat capacity at low temperatures suggest low-lying gapless spin excitations in the QSOL phase of this material. Finally, we conclude that the effective SOC realised in $d^4$ iridates are unlikely to offer a ground state which will be consistent with a purely atomic $j$-$j$ coupling description., Comment: 13 pages, 12 figures

Environmentalcontaminationduetohumanactivitiesisaworldwideproblemthathas ledtothedevelopmentofdifferentremediationtechniques,includingbiotechnologicalapproachessuchasphytoextractionandphytostabilization.Thesetechniquestakeadvantageofpioneerplants that naturally develop tolerance mechanisms to survive in extreme environments. A multi-techniqueandmulti-disciplinaryapproachwasappliedfortheinvestigationofHelichrysum microphyllum subsp. tyrrhenicum samples, bulk soil, and rhizospheres collected from a metal-extremeenvironment(Zn-PbmineofCampoPisano,SWSardinia,Italy).Zinc,Pb,andCd are the most abundant metals, with Zn attaining 3 w/w% in the rhizosphere solid materials, inducing oxidative stress in the roots as revealed by infrared microspectroscopy (IR). X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis coupled with synchrotron radiation-based (SR) techniques demonstrate that quartz, dolomite, and weddellite biomineralsprecipitateinroots,stems,andleaves,likelyasaresponsetoenvironmentalstress.In therhizosphere,ZnchemicalspeciationismainlyrelatedtotheZnoreminerals(smithsoniteandhydrozincite) whereas, in plant tissues, Zn is primarily bound to organic compounds such as malate,cysteine,andhistidinemoleculesthatactasmetalbindersand,eventually,detoxification agents for the Zn excess. These findings suggest that H. microphyllum subsp. tyrrhenicum has developed its own adaptation strategy to survive in polluted substrates, making it a potential candidateforphytostabilizationaimedatmitigatingthedispersionofmetalsinthesurrounding areas.

Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic properties of 5d iridates. In this paper we have experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds Pr2-xSrxMgIrO6(x = 0, 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at x = 0 to the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at x = 1. However, our detailed magnetic and electrical measurements refute any kind of HMAFM possibility in either of the doped samples. In addition, we establish that within these Pr2-xSrxMgIrO6 double perovskites, changes in Ir-oxidation states (4+ for PMIO to 5+ for PSMIO via mixed 4+/5+ for PSMIO1505) lead to markedly different magnetic behaviors. While SOC on Ir is at the root of the observed insulating behaviors for all three samples, the correlated magnetic properties of these three compounds develop entirely due to the contribution from local Ir moments. Additionally, the magnetic Pr3+ (4f(2)) ions, instead of showing any kind of ordering, only contribute to the total paramagnetic moment. It is seen that the PrSrMgIrO6 sample does not order down to 2 K despite antiferromagnetic interactions. But, the d(5) iridate Pr2MgIrO6 shows a sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed valent Pr1.5Sr0.5MgIrO6 sample the AFM transition is shifted to a much lower temperature (similar to 6 K) due to weakening of the AFM exchange.

While it was speculated that 5d4 systems would possess nonmagnetic J=0 ground state due to strong spin-orbit coupling (SOC), all such systems have invariably shown the presence of magnetic moments so far. A puzzling case is that of Ba2YIrO6, which in spite of having a perfectly cubic structure with largely separated Ir5+(d4) ions, has consistently hosted weak magnetic moments. We show from muon spin relaxation (μSR) measurements that a change in the magnetic environment of the implanted muons in Ba2YIrO6 occurs as the temperature is lowered below 10 K indicating magnetic response has a temperature dependence unlikely for a J=0 system. Interestingly, the estimated value of SOC obtained by fitting the resonant inelastic x-ray scattering (RIXS) spectrum of Ba2YIrO6 with an effective atomic many-body Hamiltonian is found to be as high as 0.39 eV, comparable to the reported value of SOC in other magnetic d4 iridates with noncubic distortion. We argue that in addition to strong SOC, the presence of intersite hopping triggers delocalization of holes, resulting in the spontaneous generation of magnetic moments. Our theoretical calculations further indicate that these moments favor the formation of spin-orbital singlets in the case of Ba2YIrO6, which is manifested in μSR experiments measured down to 60 mK.

Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic properties of 5$d$ iridates. In this paper we have experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at $x$ = 0 to the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at $x$ = 1. However, our detailed magnetic and electrical measurements refute any kind of HMAFM possibility in either of the doped samples. In addition, we establish that within these Pr$_{2-x}$Sr$_x$MgIrO$_6$ double perovskites, changes in Ir-oxidation states (4+ for PMIO to 5+ for PSMIO via mixed 4+/5+ for PSMIO1505) lead to markedly different magnetic behaviors. While SOC on Ir is at the root of the observed insulating behaviors for all three samples, the correlated magnetic properties of these three compounds develop entirely due to the contribution from local Ir moments. Additionally, the magnetic Pr$^{3+}$ (4$f^2$) ions, instead of showing any kind of ordering, only contribute to the total paramagnetic moment. It is seen that the PrSrMgIrO$_6$ sample does not order down to 2 K despite antiferromagnetic interactions. But, the $d^5$ iridate Pr$_2$MgIrO$_6$ shows a sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed valent Pr$_{1.5}$Sr$_{0.5}$MgIrO$_6$ sample the AFM transition is shifted to a much lower temperature ($\sim$ 6 K) due to weakening of the AFM exchange., Comment: 3 tables, and 8 figures

Beyond the fundamental interaction between water and rock, the active role of living organisms in the formation of new minerals stable at the Earth's surface must be considered (Velde & Barré, 2009). Transformation of primary minerals caused by biological degradation is up to several orders of magnitude faster than transformation of minerals due to water-rock interaction. In the rhizosphere, root exudates and associated soil microorganisms promote mineral alteration, precipitation of new phases, and the transfer of macro- and micro-nutrients from minerals to plants (Cabala et al., 2004). The reported processes allow plant utilization in remediation actions through phytostabilization strategies. In our study we selected an endemic shrub, Helichrysum microphyllum Cambess. subsp. tyrrhenicum Bacch., Brullo & Giusso (hereafter H. tyrrhenicum), growing on a Zn-Pb ore lotation tailings pond (Campo Pisano mine, Sardinia, Italy). Quartz and dolomite were detected in the bulk soil and in the rhizosphere, whereas phyllosilicates and pyrite were found only in the rhizosphere. The bulk soil is characterized by the presence of goethite, gypsum and jarosite. Pyrite probably precipitates at the soil-root interface because of the synergistic action of roots and associated microorganisms thus controlling rhizosphere mineralogy. In H. tyrrhenicum roots we detected the same minerals of the rhizosphere, suggesting that minerals are embedded in plant tissues. Soil-to-plant transfer of Zn by H. tyrrhenicum was characterized by Zn accumulation in plant roots (Znroots 2900-4000 mg/kg). The Zn coordination environment changes from the rhizosphere (mainly hydrozincite, Zn sulfate and Zn acetate) to the plant roots (mainly Zn apatite) pointing out an active role of the physiological mechanisms of the plants in incorporation of Zn into the biological tissues and biomineralization (Medas et al., ?017). These inding strongly motivate future researches aimed to investigate the reaction mechanisms governing mineral evolution in the rhizosphere and the reaction kinetics in the presence or absence of mycorrhiza and soil microbes.

While it was speculated that 5$d^4$ systems would possess non-magnetic $J$~=~0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems have invariably shown presence of magnetic moments so far. A puzzling case is that of Ba$_2$YIrO$_6$, which in spite of having a perfectly cubic structure with largely separated Ir$^{5+}$ ($d^4$) ions, has consistently shown presence of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation ($\mu$SR) measurements that a change in the magnetic environment of the implanted muons in Ba$_2$YIrO$_6$ occurs as temperature is lowered below 10~K. This observation becomes counterintuitive, as the estimated value of SOC obtained by fitting the RIXS spectrum of Ba$_2$YIrO$_6$ with an atomic $j-j$ model is found to be as high as 0.39~eV, meaning that the system within this model is neither expected to possess moments nor exhibit temperature dependent magnetic response. Therefore we argue that the atomic $j-j$ coupling description is not sufficient to explain the ground state of such systems, where despite having strong SOC, presence of hopping triggers delocalisation of holes, resulting in spontaneous generation of magnetic moments. Our theoretical calculations further indicate that these moments favour formation of spin-orbital singlets in the case of Ba$_2$YIrO$_6$, which is manifested in $\mu$SR experiments measured down to 60~mK., Comment: 20 Pages, 7 Figures

The structure of the Zr atomic environment in a CaO–ZrO2–SiO2glass ceramic as a function of thermal treatments has been studied, combining X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) and anomalous XRD (a-XRD) techniques. The analysis of XRD patterns demonstrates that the devitrification process proceeds through the partial segregation of Zr-depleted phases (wollastonite-like) and Zr-rich phases (Zr oxides). The XAS and a-XRD measurements at the ZrK-edge have been exploited in order to obtain a closer insight into the atomic structure around the Zr atoms. In the as-quenched glass the Zr atom is sixfold coordinated to O atoms in an amorphous environment rich in Ca and Si. Thermal treatment firstly (T= 1273–1323 K) causes partial segregation of Zr in the form of an oxide with a tetragonal zirconia (t-ZrO2) crystalline structure. Raising the temperature (T= 1373 K) causes the formation of ZrO2crystallites in the monoclinic crystallographic phase (baddeleyite, m-ZrO2). Analysis of the XAS data shows that a considerable amount of Zr remains in an amorphous calcium silicate phase.

Since the first observation of synchrotron radiation in 1947 progress in the generation of electromagnetic radiation using particle accelerators and in experimental methods has allowed enormous progress in the fine analysis of matter. This progress has not been incremental but rather truly innovative and in some cases revolutionary. Thanks to advances in accelerator physics and technology the improvement in the characteristics of synchrotron radiation and free electron laser sources, especially brilliance, coherence and time structure, has spanned many orders of magnitude. At the same time, new methods to investigate matter have been developed which have lead to original approaches for its characterization in the domains of real and reciprocal space, energy and time. Progress in these two aspects – sources and experimental methods – has been truly synergic. While the first applications of synchrotron radiation were in the field of solid state physics, its use now is ubiquitous in all the physical and natural sciences, with also significant medical applications. “Samples” studied at beamlines range from man – made inorganic materials and devices, natural minerals and rocks, environmentally significant specimens, cultural heritage materials, biologically relevant molecules, tissues and in some cases even live human patients. The importance and societal relevance of synchrotron radiation has been recognized by the scientific community and by policy makers world wide. Due to the investment and operation costs required to operate a synchrotron radiation or free electron laser source, centralized large scale infrastructure user facilities have been developed. In recent decades there has been an evolution from the parasitic use of synchrotron radiation emitted by accelerators designed for particle physics experiments to facilities specially designed exclusively for photon science based experiments. The scientific goal of numerous important national laboratories in the world has changed from particle physics to photon science. Most industrialized and some developing countries now have a national synchrotron radiation facility; there are also important examples of international cooperation for the construction and operation of facilities, ranging from the European Synchrotron Radiation Facility in Grenoble, a major laboratory funded by a wide European collaboration, to SESAME – a UNESCO sponsored project intended also as a means to encourage collaboration and peace in the Middle East. Access to these facilities is commonly regulated by an open access policy based exclusively on merit: whoever has a good idea to use synchrotron radiation has free access to the instruments; this is a key aspect which contributes very significantly to maintain a competitive, curiosity - driven and young intellectual community all over the world. In parallel, synchrotron radiation and free electron laser sources are a key tool to meet important societal challenges in the near future, including providing essential tools to characterize nanostructures and advanced materials used in key areas of future technologies in the inorganic and bio areas; refined methods to characterized new materials and devices are essential to provide key answers in challenging areas such as, for example, those defined by the Horizon 2020 programme of the European Union, including health and wellbeing, sustainable agriculture, secure, clean and safe and efficient energy and a clean environment. This is the context within which we are proud to present this book, which reports the lecture notes of lessons held at the 12th edition of the School on Synchrotron Radiation, organized by the Italian Synchrotron Radiation Society (Società Italiana di Luce di Sincrotrone, SILS, www.synchrotron-ratiation.it) in collaboration with Elettra – Sincrotrone Trieste (www.elettra.eu). SILS is one of the oldest independent scientific societies, the objective of which is to promote synchrotron radiation in Italy in the European context. The School took place in the town of Grado (near Trieste) in September 2013 and benefited from partial financial support from COST Action MP1103 – Nanostructured materials for solid state hydrogen storage. The directors of the school were Settimio Mobilio and Gilberto Vlaic. The SILS school has become one of the most important educational events in the field of synchrotron radiation in Europe. Its important role is testified by the high number of applications (over 100 for 45 places) and the strongly international character, with participants coming from as far away as Canada, China and Iran. In the course of the two weeks duration, which included a full day devoted to a practical session at Elettra, including hands on experience at selected beamlines and data analysis, the lectures covered the fundamentals of synchrotron radiation and free electron laser emission, the interaction between electromagnetic radiation and matter, the main experimental methods and the most important and recent applications. All these aspects are included in this volume, which is organized as follows. Part A describes the emission of synchrotron and free electron laser sources and the basic aspects of beamline instrumentation; part B illustrates the fundamentals of the interaction between electromagnetic radiation and matter; part C describes the most important experimental methods, ranging from spectroscopies, diffraction and scattering, to imaging; finally, part D reports a range of applications of current topical interest.

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

We have studied the temperature induced $0 -\pi $ thermodynamic transition in Nb/PdNi/Nb Superconductor/Ferromagnetic/Superconductor (SFS) heterostructures by microwave measurements of the superfluid density. We have observed a shift in the transition temperature with the ageing of the heterostructures, suggesting that structural and/or chemical changes took place. Motivated by the electrodynamics findings, we have extensively studied the local structural properties of the samples by means of X-ray Absorption Spectroscopy (XAS) technique, and the compositional profile by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). We found that the samples have indeed changed their properties, in particular for what concerns the interfaces and the composition of the ferromagnetic alloy layer. The structural and compositional data are consistent with the shift of the $0-\pi$ transition toward the behaviour of heterostructures with different F layers. An important emerging indication to the physics of SFS is the weak relevance of the ideality of the interfaces: even in aged samples, with less-than-ideal interfaces, the temperature-induced $0-\pi$ transition is still detectable albeit at a different critical F thickness., Comment: 11 pages, 9 figures, accepted for publication on Phys. Rev. B, http://journals.aps.org/prb/

Co nanoclusters were synthesized by an inverse-micelle chemical route. The magnetic and microstructural properties of the nanoparticles have been analyzed as a function of the surfactant (AOT and DEHP) and the drying method. Microstructural analysis has been performed by TEM and XANES; magnetic properties have been studied by hysteresis loops and zero-field cooling - field cooling (ZFC-FC) curves. TEM images show 2 to 4 nm sized particles spherical in shape. XANES measurements point out a significant presence of Co3O4 with metallic Co and some Co2+ bound to the surfactant. The presence of antiferromagnetic Co3O4 explains the magnetic transition observed at low T in both ZFC-FC measurements and hysteresis loops. Finally, the presence of magnetic interactions explains the bigger effective cluster size obtained from hysteresis loops fits (6-10 nm) compared to the sizes observed by TEM (2-4 nm).

The magnetic response of nanometer sized Co nanoparticles (NP) prepared using reverse micelle solutions are presented. The use of complementary structural and morphological probes (like transmission electron microscopy, high resolution electron microscopy, X-ray absorption spectroscopy) allowed to relate the magnetic properties to the size, morphology, composition and atomic structure of the nanoparticles. All data agree on the presence of a core–shell structure of NPs made of a metallic Co core surrounded by a thin Co-oxide layer. The core–shell microstructure of NPs affects its magnetic response mainly raising the anisotropy constant.

Euphorbia pithyusa L. was used in a plant-growth-promoting assisted field trial experiment. In order to unravel the microscopic processes at the interface, thin slices of E. pithyusa roots were investigated by micro-X-ray fluorescence mapping (?-XRF). Roots and rhizosphere materials were examined by X-ray absorption spectroscopy (XAS) at the Zn K-edge, by X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Results indicate some features common to all the investigated samples: i) in the rhizosphere of E. pithyusa Zn was found to occur in different phases; ii) Si and Al are mainly concentrated in the epidermis of the roots forming a rim; iii) Zn is mostly stored in root epidermis, and does not appear coordinated to organic molecules, but mainly occurring in mineral phases such as Zn-silicates. We interpreted that roots of E. pithyusa significantly promote mineral evolution in the rhizosphere. Concomitantly, the plant uses Si and Al extracted by soil minerals to build a biomineralization rim, which is able to capture Zn. This Zn-silicate biomineralization has relevant implication for phytoremediation techniques and for further biotechnology development, which can be better designed and developed after acquiring specific knowledge of molecular processes ruling mineral evolution and biomineralization processes.

We have investigated the role of Mn3+ Jahn-Teller distortion in driving ferromagnetism in the LaMn1-xScxO3 series. The replacement of Mn by Sc in LaMnO3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaScO3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMnO3 into a nearly regular one in LaScO3. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted MnO6 octahedron and nearly regular ScO6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted MnO6 octahedra spatially ordered as in LaMnO3 and nearly regular ScO6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular MnO6 octahedra in LaMn1-xGaxO3 for x>0.5. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the Mn3+ atom is allocated. Besides, a ferromagnetic ground state is observed for x>0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around Mn3+, which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaMn1-xBxO3 (B=Sc or Ga)., The authors thank ESRF, ALBA, and Elettra Synchrotrons for granting beam time. Financial support from the Spanish MINECO (Projects No. MAT2012-38213-C02-01 and No. MAT2011-23791) and the Diputacion General de Aragón (CAMRADS) are acknowledged.

We have studied the temperature induced $0 -��$ thermodynamic transition in Nb/PdNi/Nb Superconductor/Ferromagnetic/Superconductor (SFS) heterostructures by microwave measurements of the superfluid density. We have observed a shift in the transition temperature with the ageing of the heterostructures, suggesting that structural and/or chemical changes took place. Motivated by the electrodynamics findings, we have extensively studied the local structural properties of the samples by means of X-ray Absorption Spectroscopy (XAS) technique, and the compositional profile by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). We found that the samples have indeed changed their properties, in particular for what concerns the interfaces and the composition of the ferromagnetic alloy layer. The structural and compositional data are consistent with the shift of the $0-��$ transition toward the behaviour of heterostructures with different F layers. An important emerging indication to the physics of SFS is the weak relevance of the ideality of the interfaces: even in aged samples, with less-than-ideal interfaces, the temperature-induced $0-��$ transition is still detectable albeit at a different critical F thickness., 11 pages, 9 figures, accepted for publication on Phys. Rev. B, http://journals.aps.org/prb/

Synchrotron radiation is today extensively used for fundamental and applied research in many different fields of science. Its exceptional characteristics in terms of intensity, brilliance, spectral range, time structure and now also coherence pushed many experimental techniques to previously un-reachable limits, enabling the performance of experiments unbelievable only few years ago. The book gives an up-to-date overview of synchrotron radiation research today with a view to the future, starting from its generation and sources, its interaction with matter, illustrating the main experimental technique employed and provides an overview of the main fields of research in which new and innovative results are obtained. The book is addressed to PhD students and young researchers to provide both an introductory and a rather deep knowledge of the field. It will also be helpful to experienced researcher who want to approach the field in a professional way.

We have investigated the role of Mn3+ Jahn-Teller distortion in driving ferromagnetism in the LaMn1-xScxO3 series. The replacement of Mn by Sc in LaMnO3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaScO3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMnO3 into a nearly regular one in LaScO3. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted MnO6 octahedron and nearly regular ScO6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted MnO6 octahedra spatially ordered as in LaMnO3 and nearly regular ScO6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular MnO6 octahedra in LaMn1-xGaxO3 for x>0.5. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the Mn3+ atom is allocated. Besides, a ferromagnetic ground state is observed for x>0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around Mn3+, which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaMn1-xBxO3 (B=Sc or Ga).

We performed near-edge x-ray absorption spectroscopy at the V K edge in the antiferromagnetic insulating (AFI) phase of a 2.8% Cr-doped V2O3 single crystal. Linear dichroism of several percent is measured in the hexagonal plane and found to be in good agreement with ab initio calculations based on multiple scattering theory. This experiment definitively proves the structural origin of the signal and therefore solves a controversy raised by previous interpretations of the same dichroism as nonreciprocal. It also calls for a further investigation of the role of the magnetoelectric annealing procedure in cooling to the AFI phase.

Hole-doped perovskites such as La1-xCaxMnO3 present special magnetic and magnetotransport properties, and it is commonly accepted that the local atomic structure around Mn ions plays a crucial role in determining these peculiar features. Therefore experimental techniques directly probing the local atomic structure, like x-ray absorption spectroscopy (XAS), have been widely exploited to deeply understand the physics of these compounds. Quantitative XAS analysis usually concerns the extended region [extended x-ray absorption fine structure (EXAFS)] of the absorption spectra. The near-edge region [x-ray absorption near-edge spectroscopy (XANES)] of XAS spectra can provide detailed complementary information on the electronic structure and local atomic topology around the absorber. However, the complexity of the XANES analysis usually prevents a quantitative understanding of the data. This work exploits the recently developed MXAN code to achieve a quantitative structural refinement of the Mn K-edge XANES of LaMnO3 and CaMnO3 compounds; they are the end compounds of the doped manganite series LaxCa1-xMnO3. The results derived from the EXAFS and XANES analyses are in good agreement, demonstrating that a quantitative picture of the local structure can be obtained from XANES in these crystalline compounds. Moreover, the quantitative XANES analysis provides topological information not directly achievable from EXAFS data analysis. This work demonstrates that combining the analysis of extended and near-edge regions of Mn K-edge XAS spectra could provide a complete and accurate description of Mn local atomic environment in these compounds.

Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9, have been studied over a significant period of time in order to understand the unusual magnetism of ruthenium metal. However, among them, the M=Fe compound appears different since it is observed that unlike others, the 3d Fe ions and 4d Ru ions can easily exchange their crystallographic positions and as a result many possible magnetic interactions become realizable. The present study involving several experimental methods on this compound establish that the magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H ruthenates. Local structural study reveals that the possible Fe/Ru-site disorder further extends to create local chemical inhomogeneity, affecting the high temperature magnetism of this material. There is a gradual decrease of 57Fe M\"ossbauer spectral intensity with decreasing temperature (below 100 K), which reveals that there is a large spread in the magnetic ordering temperatures, corresponding to many spatially inhomogeneous regions. However, finally at about 25 K, the whole compound is found to take up a global glass-like magnetic ordering., Comment: 24 page, 7 figures

We present a detailed analysis of the local ordering in CoPt3 nanostructures epitaxially grown on WSe20001 and NaCl001 low-energy surfaces. Polarized extended x-ray absorption fine-structure measurements at the Co K-edge show a local structural anisotropy in fcc CoPt3 nanostructures grown at 300 K on WSe2. It is characterized by preferential Co-Co bonding along the in-plane direction balanced with preferential heteroatomic bonding along the out-of-plane direction and explains the unexpected perpendicular magnetic anisotropy. Such anisotropy almost vanishes in partially L12-ordered nanostructures grown at 700 K. In contrast, the short-range order is isotropic in CoPt3 nanostructures grown on NaCl001 at 370 K. These different behaviors emphasize the favorable role of Se segregated atoms of WSe2 in the dynamic segregation of Pt atoms at the advancing surface during codeposition, which governs the local structural anisotropy. In the absence of Se, as previously observed in epitaxial CoPt3 films grown on Ru buffer layers, the development of similar structural anisotropy requires higher growth temperatures 550-720 K.

Nanocrystalline titania pigments were produced by a novel synthesis route consisting of a high temperature forced hydrolysis in a coordinating high-boiling solvent. The effect of synthesis conditions as well as doping with Cr, Sb and V on the particle size and on the anatase-to-rutile transformation was studied by temperature-resolved synchrotron powder diffraction. The experiments were performed directly on as-synthesized low concentration suspensions of titania nanoparticles (up to 230°C) and on dried titania nanoparticles (up to 950°C). Crystallite size of as-synthesized nanoparticles is in the 5 to 50 nm range, being affected by the synthesis conditions as well as by doping and exhibits a slow-rate coarsening trend with temperature. The anatase-to-rutile transformation is drastically influenced by both synthesis conditions and doping. In particular, doping affected the anatase-to-rutile transformation rate, while the synthesis conditions influenced the phase composition, causing the appearance of brookite.

The iron sulfate FeOHSO4 studied was obtained as a dehydration product of metahohmannite Fe2(H2O)4[O(SO4)2] during a synchrotron real-time powder diffraction experiment. As quoted in the literature, FeOHSO4 has iron atoms octahedrally coordinated with two hydroxyl groups and four sulfate O atoms, while each hydroxyl group is bonded to two iron atoms. This compound is commonly described in the orthorhombic system with space group Pnma, lattice parameters aJ = 7.33, bJ = 6.42, and cJ = 7.14 Å (aJ, bJ, and cJ are the Johansson lattice parameters), and Z = 4. However a preliminary Rietveld refinement of the pattern at about 220 °C using the structural model from the literature yielded a poor fit of the observed data and a final Rp value of about 23%. A careful analysis of the calculated powder diffraction pattern showed unexpected peaks, not observed in the experimental trace, for h = 2n + 1, while sharp reflections for h = 2n seemed to point to different lattice constants and space group. The recognition of the order-disorder character of the FeOHSO4 compound was the key to successfully interpreting the unexpected features of the experimental powder pattern and the misfit with respect to the calculated pattern. In fact, FeOHSO4 belongs to a family of OD structures formed by equivalent layers of symmetry Pbmm. Only two MDO (Maximum Degree of Order) polytypes are possible. MDO1 results from a regular alternation of stacking operators 21/2 and 2−1/2, and yields an orthorhombic structure with space group Pnma and lattice parameters aJ = 7.33, bJ = 6.42, and cJ = 7.14 Å. MDO2 results from the 21/2|21/2 |21/2... sequence of symmetry operators and yields a monoclinic structure with space group P21/c, aM = 7.33, bM = 7.14, cM = 7.39 Å, and β = 119.7°. The analysis of one-dimensional stacking disorder was performed by fitting the observed XRPD pattern with a calculated intensity curve generated by DIFFaX. The disorder model was investigated by taking into account a probability matrix for the occurrence of OD layer sequences. The best fit (Rp = 0.009) to the observed powder pattern was obtained with a 61:39 ratio of monoclinic and orthorhombic polytypes for a fully disordered OD layers sequence.

We performed near-edge x-ray absorption spectroscopy (XANES) at V K edge in the antiferromagnetic insulating (AFI) phase of a 2.8% Cr-doped V_2O_3 single crystal. Linear dichroism of several percent is measured in the hexagonal plane and found to be in good agreement with ab-initio calculations based on multiple scattering theory. This experiment definitively proves the structural origin of the signal and therefore solves a controversy raised by previous interpretations of the same dichroism as non-reciprocal. It also calls for a further investigation of the role of the magnetoelectric annealing procedure in cooling to the AFI phase., Comment: 4 pages 3 figures. To be published in Phys. Rev. B (2005)

International audience; Structural and magnetic properties of nanocrystalline compounds of the general formula La1-xMnO3+δ have been investigated combining x-ray diffraction and x-ray absorption spectroscopy in order to achieve an accurate description of the sample atomic structure in relation with its magnetic properties. The study reveals the segregation of different phases instead of a homogeneous sample composition. Interesting is the segregation of a vacancy-doped phase LayMnO3 whose composition is the same (y~0.9) for all the investigated samples, independently of the average sample composition. Since this phase is found to be principally responsible for the magnetic properties of these compounds, such a phase separation explains the largely composition-independent magnetic properties observed in the range 0.9>~La/Mn>~0.7.

Cu(II) binding to the alpha prion protein (alphaPrP) can be both intramolecular and intermolecular. X-ray absorption spectroscopy at the copper K-edge has been used to explore the site geometry under each binding mode using both insoluble polymeric Cu(II).alphaBoPrP-(24-242) (bovine PrP) complexes and soluble Cu(II) complexes of peptides containing one, two, and four copies of the octarepeat. Analysis of the extended region of the spectra using a multiple scattering approach revealed two types of sites differing in the number of His residues in the first coordination shell of Cu(II). Peptides containing one and two-octarepeat copies in sub-stoichiometric Cu(II) complexes showed the direct binding of a single His in accord with crystallographic intra-repeat geometry. Alternatively, the polymeric Cu(II).alphaBoPrP-(24-242) complex and Cu(II) in its soluble complex with a four-octarepeat peptide at half-site-occupancy showed Cu(II) directly bound to two His residues, consistent with an inter-repeat binding mode. Increasing the Cu(II) site occupancy from 0.5 to 0.75 in the peptide containing four octarepeats resulted in spectral features that are intermediate to those of the inter- and intra-repeat modes. The transition from His-Cu-His (inter-repeat) to Cu-His (intra-repeat) on increasing Cu(II) saturation offers a structural basis for the positive cooperativity of the cation binding process and explains the capacity of alphaPrP to participate in Cu(II)-mediated intermolecular interactions.

The interface structure of epitaxial Fe/Cr multilayers was studied using anomalous X-ray and neutron reflectivity. The analysis of X-ray reflectivity at three different energies provided a reliable information about the interface roughnesses. It is found that the Cr-on-Fc interface is more diffused as compared to the Fe-on-Cr interface and that the roughness exhibits a significant increase with increasing depth. The magnetic roughness, as determined from neutron reflectivity, is lower than the geometrical roughness, in conformity with the behavior of a number of magnetic thin films and multilayers. (C) 2004 Elsevier B.V. All rights reserved