Disentangling multipole resonances through a full x-ray polarization analysis

Complete polarization analysis applied to resonant x-ray scattering at the Cr K-edge in K2CrO4 shows that incident linearly polarized x-rays can be converted into circularly polarized x-rays by diffraction at the Cr pre-edge (E = 5994 eV). The physical mechanism behind this phenomenon is a subtle interference effect between purely dipole (E1-E1) and purely quadrupole (E2-E2) transitions, leading to a phase shift between the respective scattering amplitudes. This effect may be exploited to disentangle two close-lying resonances that appear as a single peak in a conventional energy scan, in this way allowing to single out and identify the different multipole order parameters involved.Comment: 6 pages, 6 figure

Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study

A synchrotron x-ray diffraction study of the crystallographic structure of PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the oxygen sublattice, which was previously ambiguous, is shown to be a chiral structure in which neighbouring oxygen chains have opposite chiralities. A temperature dependent study of the magnetic excitation spectrum, probed by neutron inelastic scattering, is also reported. Changes in the energies and relative intensities of the crystal field transitions provide an insight into the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure

KINETICS OF THE COMPUTER-SIMULATED TENNIS STROKE WITH DIFFERENT RACKETS

INTRODUCTION: The aim of this biomechanical analysis of the tennis stroke is the determination of the effects of the mass properties of different tennis rackets' on the kinetics of the striking arm. In contrast to experimental investigation the computer simulation gives an infinite temporal resolution so that the arm movements could be investigated especially during the racket-ball-contact phase. The planar model of the tennis stroke consisting of the immovable trunk, the upper arm, the lower arm, the hand and• the racket was derived from the mo ei of the human body by GLITSCH (1993). The striking arm with a racket tightly fixed to the hand was constructed as a pendulum of three rigid bodies which are connected with frictionless revolute joints. An elastic spring (0=45000 N/m) represents the ballracket-contact. The arm-racket-system• rotates around the shoulder joint and hits the resting ball in the respective" racket area centre. Considering rigid body mechanics the mass distributions of three different tennis rackets were measured and served as input for the model. The computer simulation with the initial conditions referring to real tennis strakes registered by KNUDSON (1990) was carried out with the software-packet DADS (Dynamic Analysis and Design System) by CADSI (Computer Aided Design Software Inc.). RESULTS: As it is shown in figure 1 the computer simulation has calculated an elbow flexion when rackets 1 or 2 are used. When the tennis forehand stroke is carried out with racket 3 the elbow is kept extended during the ball-racket-contact phase. The quite different arm movements during the impact with different tennis rackets are the result• of the separate locations of the centres of percussion with respect to the rigid handracket-system. The centre of percussion of racket 3 (5.3 cm) is located more distally than its centre of area because of the different mass distribution and finally because of its greater moment of inertia. In contrast to that the centre of percussion of the other two rackets (racket 1: -3.6 cm, racket 2: -3A cm) are located more proximally than the hitting point. CONCLUSION: The mechanical properties of tennis rackets, particularly the mass distribution, are responsible for different and movements during the ball-racket-contact phase. Obviously, there is no consensus of the preferable mass distribution of modern tennis rackets. This model can objectively assist in choosing one's individual favourable racket. REFERENCES: Glitsch U., Farkas R. (1993): Applications of a multi-body simulation model in human movement studies. Proc. Int. Soc. of Biomech., XIV1h congress, Paris. Knudson, DV (1990): Intrasubject variability of upper extremity angular kinematics on the tennis forehand drive. Int. J. of Sport Biomech., 6, 415-421

X-ray polarization: General formalism and polarization analysis

The polarization of x-rays plays an outstanding role in experimental techniques such as non-resonant magnetic x-ray scattering and resonant x-ray scattering of magnetic and multipolar order. Different instrumental methods applied to synchrotron light can transform its natural polarization into an arbitrary polarization state. Several synchrotron applications, in particular in the field of magnetic and resonant scattering rely on the improvement in the signal/noise ratio or the deeper insight into the ordered state and the scattering process made possible through these polarization techniques. Here, we present the mathematical framework for the description of fully and partially polarized x-rays, with some applications such as linear x-ray polarization analysis for the determination of the scattered beam's polarization, and the Ge K-edge resonant scattering.Comment: 12 pages, 6 figures and 1 table. To be published in proceedings of the workshop "Resonant Elastic X-ray Scattering", Aussois, France (2011

Mean-field model of the ferromagnetic ordering in the superconducting phase of ErNi_2B_2C

A mean-field model explaining most of the details in the magnetic phase diagram of ErNi_2B_2C is presented. The low-temperature magnetic properties are found to be dominated by the appearance of long-period commensurate structures. The stable structure at low temperatures and zero field is found to have a period of 40 layers along the a direction, and upon cooling it undergoes a first-order transition at T_C = 2.3 K to a different 40-layered structure having a net ferromagnetic component of about 0.4 mu_B/Er. The neutron-diffraction patterns predicted by the two 40-layered structures, above and below T_C, are in agreement with the observations of Choi et al.Comment: 4 pages, 3 figures (Revtex4

Lockin to Weak Ferromagnetism in TbNi2B2C and ErNi2B2C

This article describes a model in which ferromagnetism necessarily accompanies a spin-density-wave lockin transition in the borocarbide structure provided the commensurate phase wave vector satisfies Q = (m/n)a* with m even and n odd. The results account for the magnetic properties of TbNi2B2C, and are also possibly relevant also for those of ErNi2B2C.Comment: 4 page

High-field irreversible moment reorientation in the antiferromagnet Fe1.1_{1.1}Te

Magnetization measurements have been performed on single-crystalline Fe$_{1.1}$Te in pulsed magnetic fields $\mathbf{H}\perp\mathbf{c}$ up to 53 T and temperatures from 4.2 to 65 K. At $T=4.2$ K, a non-reversible reorientation of the antiferromagnetic moments is observed at $\mu_0H_R=48$ T as the pulsed field is on the rise. No anomaly is observed at $H_R$ during the fall of the field and, as long as the temperature is unchanged, during both rises and falls of additional field pulses. The transition at $H_R$ is reactivated if the sample is warmed up above the N\'{e}el temperature $T_N\simeq60$ K and cooled down again. The magnetic field-temperature phase diagram of Fe$_{1.1}$Te in $\mathbf{H}\perp\mathbf{c}$ is also investigated. We present the temperature dependence of $H_R$, as well as that of the antiferromagnetic-to-paramagnetic borderline $H_c$ in temperatures above 40 K.Comment: 5 pages, 4 figure

Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: evidence for the double-q model

Recent theoretical efforts aimed at understanding the nature of antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we employ resonant elastic x-ray scattering to test this theory against the formerly proposed, single-q ordering scenario. Our study reveals a satellite reflection associated with a mixed-order component propagation wave vector, viz., (q_a,2q_b,0) with q_b = q_a approx= 0.55 reciprocal lattice units, the presence of which is incompatible with single-q ordering but is expected from the double-q model. A (3q_a,0,0) wave vector (i.e., third-order) satellite is also observed, again in line with the double-q model. The temperature dependencies of these along with that of a first-order satellite are compared with calculations based on the double-q model and reasonable qualitative agreement is found. By examining the azimuthal dependence of first-order satellite scattering, we show the magnetic order to be, as predicted, elliptically polarized at base temperature and find the temperature dependence of the "out of a-b plane" moment component to be in fairly good agreement with calculation. Our results provide qualitative support for the double-q model and thus in turn corroborate the explanation for the "magnetoelastic paradox" offered by this model.Comment: 8 pages, 5 figures. Submitted to Phys. Rev.