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Two distinct ferromagnetic phases are present in LaMn0.5Co0.5O3 for which the spin-only magnetic moment calculated from the high temperature dc susceptibility is found to be unusually high. Such a high moment can only be accounted for by assigning the valence state of the cations to Mn2+-Co4+. This is unrealistic as the earlier report based on X-ray absorption spectroscopy (XAS) has suggested the valence state to be mainly Mn4+-Co2+ with traces of Co3+. Also from our studies using XAS, it is found that the valence state is mainly Mn4+-Co2+. In addition, no notable difference is observed in the minor Co3+ present in both phases. Our results based on X-ray magnetic circular dichroism studies (XMCD) reveal the presence of ``distinct'' high orbital moment associated with Co2+ for both phases. Thus it is found that the distinctness of the orbital moment also plays a vital role in determining the magnetic moment and T-c of both phases of LaMn0.5Co0.5O3. By considering the orbital moment obtained from XMCD, the anomaly in the paramagnetic susceptibility is resolved and thus we are able to assign the valence state to Mn4+-Co2+ configuration. The difference in the magnitude of orbital moment in both phases is believed to be due to the crystal field effects.

Highly collimated synchrotron sources are the essential ingredient of novel radiology and micro-radiology techniques for materials science. medicine and biology-with contrast based on the refractive index rather than on absorption. We were able to implement a real-time version of such techniques. Successful test studies included thin-foil breaking and electrodeposition processes in the areas concerning materials properties. Meanwhile. extensive effort was dedicated to obtain high-quality X-ray images of live specimens on a microscopic scale and in real time. These tests achieved a lateral resolution better than 2 mum and a time per image of 10 ms, with clear potential for further improvements. The images revealed in great detail moving parts of different specimens. opening the way to a wide variety of applications in the life sciences, medicine and materials science. (C) 2001 Published by Elsevier Science B.V.

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ∼16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. Fil: Meech, K. J.. Institute for Astronomy; Estados Unidos Fil: A’Hearn, M. F.. University of Maryland; Estados Unidos Fil: Adams, J. A.. Cornell University; Estados Unidos Fil: Bacci, P.. Centro Astronomico di Libbiano; Italia Fil: Bai, J.. Chinese Academy of Sciences; China Fil: Barrera, L.. Universidad Metropolitana de Ciencias de la Educacion; Chile Fil: Battelino, M.. Swedish Space Corporation; Suecia Fil: Bauer, J. M.. Jet Propulsion Laboratory; Estados Unidos Fil: Becklin, E.. Stratospheric Observatory for Infrared Astronomy; Estados Unidos Fil: Bhatt, B.. Indian Institute of Astrophysics; India Fil: Biver, N.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bockelee Morvan, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bodewits, D.. University of Maryland; Estados Unidos Fil: Bohnhardt, H.. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; Alemania Fil: Boissier, J.. Inst. di Radioastronomia; Italia Fil: Bonev, B. P.. Catholic University of America; Estados Unidos Fil: Borghini, W.. Osservatorio Astronomico Naturalistico di Casasco; Italia Fil: Brucato, J. R.. Osservatorio Astrofisico di Arcetri; Italia Fil: Bryssinck, E.. Brixiis Observatory; Bélgica Fil: Buie. M. W.. Southwest Research Institute; Estados Unidos Fil: Canovas, H.. Utrecht University; Países Bajos Fil: Castellano, D.. Unione Astrofili Italiani; Italia Fil: Charnley, S. B.. National Aeronautics And Space Administration; Estados Unidos Fil: Chen, W. P.. National Taiwan Normal University; Corea del Sur Fil: Chiang, P.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Choi, Y. J.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Christian, D. J.. California State University; Estados Unidos Fil: Chuang, Y. L.. National Taiwan Normal University; Corea del Sur Fil: Cochran, A. L.. University of Texas; Estados Unidos Fil: Melita, Mario Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Soft x-ray absorption experiments on the transition-metal ${L}_{2,3}$ edge of multiferroic ${\text{MnWO}}_{4}$ and antiferromagnetic ${\text{CoWO}}_{4}$ are presented. The observed linear polarization dependence, analyzed by full-multiplet calculations, is used to determine the ground-state wave function of the magnetic ${\text{Mn}}^{2+}$ and ${\text{Co}}^{2+}$ ions. The impact of the local structure and the spin-orbit coupling on the orbital moment is discussed in terms of the single-ion anisotropy. It is shown that the orbital moment in ${\text{CoWO}}_{4}$ is responsible for the collinear antiferromagnetism, while the small size of spin-orbit coupling effects make spiral magnetic order in ${\text{MnWO}}_{4}$ possible, enabling the material to be multiferroic.

Linear-polarized soft-x-ray absorption (XAS) and inelastic neutron scattering (INS) experiments have been performed on $\text{Ce}M{\text{In}}_{5}$ with $M=\text{Rh}$, Ir, and Co to determine the crystal-field scheme and characteristic Kondo temperatures ${T}^{\ensuremath{\ast}}$ for the hybridization between $4f$ and conduction electrons. The ground-state wave functions are determined from the polarization-dependent soft-XAS data at the cerium ${M}_{4,5}$ edge and the crystal-field splittings from INS. The characteristic temperature ${T}^{\ensuremath{\ast}}$ has been determined from the line widths of the neutron scattering data. We find that the quasielastic linewidths of the superconducting compounds ${\text{CeCoIn}}_{5}$ and ${\text{CeIrIn}}_{5}$ are comparable with the low-energy crystal-field splitting.

We present a combined experimental and theoretical x-ray absorption spectroscopy study of the class of cobaltates ${\text{YBaCo}}_{4}{\text{O}}_{7}$ and ${\text{YBaCo}}_{3}M{\text{O}}_{7}$ $(M=\text{Al},\text{ }\text{Fe})$. The focus is on the local electronic and magnetic properties of the transition metal ions in these geometrically frustrated kagom\'e compounds. For the mixed valence cobaltate ${\text{YBaCo}}_{4}{\text{O}}_{7}$, both the ${\text{Co}}^{2+}$ and ${\text{Co}}^{3+}$ are found to be in the high-spin state. The stability of these high-spin states in tetrahedral coordination is compared with those in the more studied case of octahedral coordination. For the compound ${\text{YBaCo}}_{3}{\text{FeO}}_{7}$, we find exclusively ${\text{Co}}^{2+}$ and ${\text{Fe}}^{3+}$ as charge states.

Using $\mathrm{Co}\mathrm{\text{\ensuremath{-}}}{L}_{2,3}$ and $\mathrm{O}\mathrm{\text{\ensuremath{-}}}K$ x-ray absorption spectroscopy, we reveal that the charge ordering in ${\mathrm{La}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_{4}$ involves high spin ($S=3/2$) ${\mathrm{Co}}^{2+}$ and low spin ($S=0$) ${\mathrm{Co}}^{3+}$ ions. This provides evidence for the spin-blockade phenomenon as a source for the extremely insulating nature of the ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{4}$ series. The associated ${e}_{g}^{2}$ and ${e}_{g}^{0}$ orbital occupation accounts for the large contrast in the Co-O bond lengths and, in turn, the high charge ordering temperature. Yet, the low magnetic ordering temperature is naturally explained by the presence of the nonmagnetic ($S=0$) ${\mathrm{Co}}^{3+}$ ions. From the identification of the bands we infer that ${\mathrm{La}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_{4}$ is a narrow band material.

We have studied the local electronic structure of $\mathrm{La}{\mathrm{Mn}}_{0.5}{\mathrm{Co}}_{0.5}{\mathrm{O}}_{3}$ using soft-x-ray absorption spectroscopy at the $\mathrm{Co}\text{\ensuremath{-}}{L}_{3,2}$ and $\mathrm{Mn}\text{\ensuremath{-}}{L}_{3,2}$ edges. We found a high-spin ${\mathrm{Co}}^{2+}\text{\ensuremath{-}}{\mathrm{Mn}}^{4+}$ valence state for samples with the optimal Curie temperature. We discovered that samples with lower Curie temperatures contain low-spin nonmagnetic ${\mathrm{Co}}^{3+}$ ions. Using soft-x-ray magnetic circular dichroism, we established that the ${\mathrm{Co}}^{2+}$ and ${\mathrm{Mn}}^{4+}$ ions are ferromagnetically aligned. We also revealed that the ${\mathrm{Co}}^{2+}$ ions have a large orbital moment: ${m}_{\mathrm{orb}}∕{m}_{\text{spin}}\ensuremath{\approx}0.47$. Together with model calculations, this suggests the presence of a large magnetocrystalline anisotropy in the material and predicts a nontrivial temperature dependence for the magnetic susceptibility.

We infer that soft-x-ray absorption spectroscopy is a versatile method for the determination of the crystal-field ground state symmetry of rare earth heavy fermion systems, complementing neutron scattering. Using realistic and universal parameters, we provide a theoretical mapping between the polarization dependence of Ce ${M}_{4,5}$ spectra and the charge distribution of the Ce $4f$ states. The experimental resolution can be orders of magnitude larger than the $4f$ crystal-field splitting itself. To demonstrate the experimental feasibility of the method, we investigated ${\mathrm{CePd}}_{2}{\mathrm{Si}}_{2}$, thereby settling an existing disagreement about its crystal-field ground state.

We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

We found direct experimental evidence for an orbital switching in the V $3d$ states across the metal-insulator transition in ${\mathrm{VO}}_{2}$. We have used soft-x-ray absorption spectroscopy at the V ${L}_{2,3}$ edges as a sensitive local probe and have determined quantitatively the orbital polarizations. These results strongly suggest that, in going from the metallic to the insulating state, the orbital occupation changes in a manner that charge fluctuations and effective bandwidths are reduced, that the system becomes more one dimensional and more susceptible to a Peierls-like transition, and that the required massive orbital switching can only be made if the system is close to a Mott insulating regime.

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in ${\mathrm{L}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}$ is strongly reduced from its ionic value, both below and above the N\'eel temperature. Using Ti ${L}_{2,3}$ x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the ${t}_{2g}$ subshell is about 0.12--0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.

We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase ${\mathrm{T}\mathrm{i}\mathrm{O}}_{2}$ thin film, using the magnetic circular dichroism (MCD) at the Co ${L}_{2,3}$ absorption edges. The magnetic moment was observed to be $\ensuremath{\sim}0.1{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$ in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at $\ensuremath{\sim}400\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the MCD signal increases, and the moment reaches up to $\ensuremath{\sim}1.55{\ensuremath{\mu}}_{B}/\mathrm{C}\mathrm{o}$, which is $\ensuremath{\sim}90%$ of the moment in Co metal. In the latter case, the cluster size was observed to be 20--60 nm.

author, Room-temperature thermoelectric power S^290 as a function of hole concentration per planer Cu atom (P_pl) has been studied in a chain-free double-layer Y_1−_xCa_xBa_2Cu_3O_6. S^290(P_pl) of Y_1−_xCa_xBa_2Cu_3O_6 (P_pl=x/2) behaves identically to that of single-layer La_2−_xSr_xCuO_4 (P_pl=x). In order to show the validity of the present scale of S^290(P_pl), we demonstrate the phase diagram for bilayer Yba_2Cu_3O_y system and Bi_2Sr_2CaCu_2O_y system and discuss.

Honma, T; Hor, PH; Hsieh, HH; Tanimoto, M, Physical Review B, 70(21), 214517, 2004. "Copyright 2004 by the American Physical Society."http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRBMDO000070000021214517000001&idtype=cvips&gifs=Yes publisher, We have measured thermoelectric power (TEP) as a function of hole concentration per CuO2 layer Ppl in Y1−xCaxBa2Cu3O6 sPpl=x/2d with no oxygen in the Cu-O chain layer. The room-temperature TEP as a function of Ppl, S290sPpld, of Y1−xCaxBa2Cu3O6 behaves identically to that of La2−zSrzCuO4 sPpl=zd. We argue that S290sPpld represents a measure of the intrinsic equilibrium electronic states of doped holes and, therefore, can be used as a common scale for the carrier concentrations of layered cuprates. We shows that the Ppl determined by this new universal scale is consistent with both hole concentration microscopically determined by NQR and the hole concentration macroscopically determined by the formal valency of Cu. We find two characteristic scaling temperatures, TS * and TS2 * , in the TEP versus temperature curves that change systematically with doping. Based on the universal scale, we uncover a universal phase diagram in which almost all the experimentally determined pseudogap temperatures as a function of Ppl fall on two common curves; lower pseudogap temperature defined by the TS * versus Ppl curve and upper pseudogap temperature defined by the TS2 * versus Ppl curve. We find that while pseudogaps are intrinsic properties of doped holes of a single CuO2 layer for all high-Tc cuprates, Tc depends on the number of layers, therefore, the inter layer coupling, in each individual system.

Tests performed in different regimes reveal the interplay of two edge-enhancement mechanisms in radiological images taken with coherent synchrotron light. The relative weight of the two mechanisms, related to refraction and to Fresnel edge diffraction, can be changed in a controlled way. This makes it possible to obtain different images of the same object with complementary information. (C) 1999 American Institute of Physics. [S0021-8979(99)03720-2].