Time-resolved X-ray microscopy of nanoparticle aggregates under oscillatory shear

Of all current detection techniques with nanometer resolution, only X-ray microscopy allows imaging nanoparticles in suspension. Can it also be used to investigate structural dynamics? When studying response to mechanical stimuli, the challenge lies in applying them with precision comparable to spatial resolution. In the first shear experiments performed in an X-ray microscope, we accomplished this by inserting a piezo actuator driven shear cell into the focal plane of a scanning transmission X-ray microscope (STXM). Thus shear-induced reorganization of magnetite nanoparticle aggregates could be demonstrated in suspension. As X-ray microscopy proves suitable for studying structural change, new prospects open up in physics at small length scales.Comment: submitted to J. Synchrot. Radia

Exploring small energy scales with x-ray absorption and dichroism

Soft x-ray linear and circular dichroism (XLD, XMCD) experiments at the Ce M$_{4,5}$ edges are being used to determine the energy scales characterizing the Ce $4f$ degrees of freedom in the ultrathin ordered surface intermetallic CeAg$_x$/Ag(111). We find that all relevant interactions, i. e. Kondo scattering, crystal field splitting and magnetic exchange coupling occur on small scales. Our study demonstrates the usefulness of combining x-ray absorption experiments probing linear and circular dichroism owing to their strong sensitivity for anisotropies in both charge distribution and paramagnetic response, respectively.Comment: 5 pages, 4 figure

Is There a Sex Difference in the Age of Elite Marathon Runners?

Purpose: The purposes of this study were to determine i) if there is a sex difference in the age of the elite marathon runners and ii) if the sex difference in performance altered across the years that women have participated in the marathon. Methods: Age at time of competition and running times of the first five placed male and female runners who competed in the seven marathons of the World Marathon Majors Series were analyzed. Data from as many years as was available online were retrieved so that 410 men and 410 women were included in the analysis. The marathons and years included the Berlin (1999–2009), Boston (2000–2009), Chicago (1997–2009), London (2001–2009), New York City (1990–2009), International Athletic Association Federation World Championship (1983, 1987, and every 2 yr from 1991), and Olympic (every 4 yr since 1984) marathons. Results: Women were older than men (mean ± SD = 29.8 ± 4.2 vs 28.9 ± 3.8 yr), but for only two of the seven marathons, the Chicago and the London marathons (P \u3c 0.05): the sex difference in age was not consistent across the years. There was no sex difference in age for the Berlin, Boston, New York City, World Championship, and Olympic marathons. Men were faster than women (11.6% ± 1.8%). The sex difference in running velocity varied across marathons (least for the World Championships, 10.2%) and also across years, but not systematically. This sex difference in running velocity increased from first to fifth place across all marathons. Conclusions: These data indicate that men and women physiologically peak at a similar age in marathon running performance. The sex difference in performance of elite marathon runners varied across years but has not systemically decreased or varied since the 1980s

Electronic tuneability of a structurally rigid surface intermetallic and Kondo lattice: CePt5_5 / Pt(111)

We present an extensive study of structure, composition, electronic and magnetic properties of Ce--Pt surface intermetallic phases on Pt(111) as a function of their thickness. The sequence of structural phases appearing in low energy electron diffraction (LEED) may invariably be attributed to a single underlying intermetallic atomic lattice. Findings from both microscopic and spectroscopic methods, respectively, prove compatible with CePt$_5$ formation when their characteristic probing depth is adequately taken into account. The intermetallic film thickness serves as an effective tuning parameter which brings about characteristic variations of the Cerium valence and related properties. Soft x-ray absorption (XAS) and magnetic circular dichroism (XMCD) prove well suited to trace the changing Ce valence and to assess relevant aspects of Kondo physics in the CePt$_5$ surface intermetallic. We find characteristic Kondo scales of the order of 10$^2$ K and evidence for considerable magnetic Kondo screening of the local Ce $4f$ moments. CePt$_5$/Pt(111) and related systems therefore appear to be promising candidates for further studies of low-dimensional Kondo lattices at surfaces.Comment: 14 pages, 11 figure

Magnetostructural behavior in the non-centrosymmetric compound Nd7Pd3

A systematic study of the physical properties and microscopic magnetism of Nd7Pd3 compound, which in the paramagnetic state crystallizes in the non-centrosymmetric hexagonal Th7Fe3-type structure (hP20–P63 mc; with a  =  10.1367(1) Å and c  =  6.3847(1) Å at 300 K), confirms multiple magnetic ordering transitions that occur upon cooling. Antiferromagnetic transition is observed at T N  =  37 K, which is followed by ferromagnetic transformation at T C  =  33 K. The first-order magnetic transition at T C is magnetoelastic: it involves a change of crystal symmetry from P63 mc to Cmc21 and leads to anisotropic changes of the unit cell parameters. While the antiferromagnetic structure is symmetry allowed in P63 mc, the ferromagnetic structure with magnetic moments along the a-direction of the original hexagonal unit cell induces the first order transition to Cmc21. Density functional theory calculations confirm the experimentally observed ground state with the a-axis as the easy magnetization direction

Transport and Magnetic Studies on the Spin State Transition of Pr1-xCaxCoO3 up to High Pressure

Transport and magnetic measurements and structural and NMR studies have been carried out on (Pr1-yR'y)1-xAxCoO3 {R'=(rare earth elements and Y); A=(Ca, Ba and Sr)} at ambient pressure or under high pressure. The system exhibits a phase transition from a nearly metallic to an insulating state with decreasing temperature T, where the low spin (LS) state of Co3+ is suddenly stabilized. For y=0, we have constructed a T-x phase diagram at various values of the external pressure p. It shows that the (T, x) region of the low temperature phase, which is confined to a very narrow region around x=0.5 at ambient pressure, expands as p increases, suggesting that the transition is not due to an order-disorder type one. For the occurrence of the transition, both the Pr and Ca atoms seem to be necessary. The intimate relationship between the local structure around the Co ions and the electronic (or spin) state of Co3+ ions is discussed: For the smaller unit cell volume or the smaller volume of the CoO6 octahedra and for the larger tilting angle of the octahedra, the temperature of the transition becomes higher. The role of the carriers introduced by the doping of the A atoms, is also discussed. By analyzing the data of 59Co-NMR spectra and magnetic susceptibilities of Pr1-xCaxCoO3 the energy separations among the different spin states of Co3+ and Co4+ are roughly estimated.Comment: 15 pages, 15 figures, 2 tables, submitted to J. Phys. Soc. Jp

Magnetic Structures of High Temperature Phases of TbBaCo2O5.5

Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo2O5.5 in the temperature range of 7-370 K. There have been observed several magnetic or structural transitions. Among these, the existence of the transitions to the insulating phase from the metallic one at ~340 K, to the one with the ferromagnetic moment at ~280 K and possibly to the antiferromagnetic one at ~260 K, with decreasing temperature T correspond to those reported in former works. We have studied the magnetic structures at 270 K and 250 K and found that all Co3+ ions of the CoO6 octahedra are in the low spin state and those of the CoO5 pyramids carry spins which are possibly in the intermediate spin state. Non-collinear magnetic structures are proposed at these temperatures. Two other transitions have also been observed at the temperatures, ~100 K and ~250 K.Comment: 9 pages, 2 tables, 10 figure