April 2008 Archives

Spintronics is now one of the most important keywords in modern sciences and technologies. The currently employed method for magnetic recording uses electrical current pulses, and there appear to be limitations for extremely high density devices (e.g., G-bit level MRAM). One of the most promising solutions is the use of spin polarized current in a ferromagnetic medium, which can provide a spin-transfer torque to the magnetization, resulting in its motion. To develop high-density and very fast devices, it is indispensable to obtain a fundamental understanding of what really takes place there. Recently, a research group led by Dr. G. Meier (Hamburg University, Germany) succeeded in visualizing spin-torque-induced vortex gyration in micrometer-sized permalloy squares using a 30nm-resolution X-ray microscope at the Advanced Light Source (ALS), Berkeley, United States. The phases of the gyration in structures with different chirality have been analyzed considering alternating spin-polarized currents and the current's Oersted field. For more information on the present experiments, see the paper, "Time-Resolved X-Ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration", M. Bolte et al., Phys. Rev. Lett., 100, 1701 (2008).

The Japanese government has released the list of recipients of this year's spring decorations, comprising 3,973 Japanese and 51 foreign nationals, for their contributions to the nation and public in politics, business, culture and the arts. Readers of X-Ray Spectrometry would be interested to know that Sir Martin Wood, one of the founders of Oxford Instruments, received The Order of the Rising Sun, Gold Rays with Neck Ribbon. An official explanation of Japanese decorations and medals can be found at http://www8.cao.go.jp/english/decoration/index.html Wikipedia carries a comprehensive introduction at http://en.wikipedia.org/wiki/Order_of_the_Rising_Sun

Progress in nano sciences requires further development of local structural probes, particularly for the study of non-uniform materials. As material functions are often concerned with heterogeneity and some hierarchical orders of the structures, some kind of zooming from low to high resolution will become crucial in the future. Furthermore, in addition to two-dimensional (2D) imaging of an object with a lateral resolution determined by the beam size, some depth resolution is important for a better understanding of materials. So far, X-ray techniques have had several limitations with respect to such points. Recently, French scientists led by Professor J-L. Hodeau (CNRS, Grenoble, France) have reported an interesting development. They are trying to combine pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials. The experiments were for a high-pressure pellet containing several carbon phases and a heterogeneous powder containing chalcedony and iron pigments. For more information, see the paper, "Probing the structure of heterogeneous diluted materials by diffraction tomography", P. Bleuet et al., Nature Materials, 7, 468 (2008).

X-ray Bragg diffraction can determine crystal structures. So far, however, distinguishing between right- and left-handed crystals has not been done by ordinary X-ray diffraction. Japanese scientists led by Professor S. Shin (RIKEN & The University of Tokyo) recently succeeded in revealing the chirality of crystals by measuring Bragg diffraction near the absorption edge, using circular polarization of synchrotron X-rays at the SPring-8. Reflections only allowed at resonant conditions have been well interpreted for the α-quartz case. For more information, see the paper, "Right Handed or Left Handed? Forbidden X-Ray Diffraction Reveals Chirality", Y. Tanaka et al., Phys. Rev. Lett., 100, 145502 (2008).

A very useful XRS booklet has recently been published in Argentina. Seven chapters are contribution of the authors from South America (Mexico, Brazil, Venezuela and Argentina) and the rest three are from Europe (Austria and Belgium). This booklet could be used as a textbook in tutorial workshops for newcomers to XRS, because it covers a lot of ground ranging from the fundamental aspects of XRS right through to almost all the important applications, as well as providing key knowledge for practical analysis such as sample preparation. In addition, it is full of comprehensive figures, photos and tables that are large enough to view even if one is simply flipping through the pages. The booklet covers not only XRS in general, but also detailed information on TXRF, which has become particularly popular in South America. In the preface, the editor of the book, Professor Cristina Vazquez, comments on the long history of X-rays after their discovery by Roentgen in 1895. Nowadays, X-ray analysis is one of the most widely used scientific tools. Synchrotron sources are available worldwide (except unfortunately in Africa - in South America, one synchrotron is operating in Sao Paulo, Brazil). The publication of such an excellent XRS textbook (as well as the holding of good conferences and tutorial workshops) is significant in preparing the way for the next generation of students so that they too can go on to create history.

Cadmium is one of the most ecotoxic metals. A Spanish and Belgian research group led by Dr. M. Hidalgo (University of Girona, Spain) has recently reported the determination of trace Cd in complex environmental liquid samples. The method employed is basically a combination of a pre-concentration technique and Cd Kα XRF analysis with a high-energy polarized beam (PANalytical Epsilon 5 with a Gd tube, 100kV-6mA, and a Ge detector). In order to collect trace Cd effectively, the research group used Aliquat 336 (trademark of Cognis Corp.), which is tricaprylmethylammonium chloride (C₂₅H₅₄ClN), as an extractant. The typical detection limit is 0.7 μg/L, and the accuracy was investigated by using spiked seawater samples and a synthetic water sample containing, besides Cd, high amounts of other metal pollutants such as Ni, Cu, and Pb. For more information, see the paper, "High-Energy Polarized-Beam Energy-Dispersive X-ray Fluorescence Analysis Combined with Activated Thin Layers for Cadmium Determination at Trace Levels in Complex Environmental Liquid Samples", E. Margui et al., Anal. Chem., 80, 2357 (2008).

As an X-ray free-electron laser (X-FEL) provides extremely strong pulses, it is necessary to understand the photon-induced damage processes for biological samples. A research group led by Dr. Chapman (DESY, Germany and Lawrence Livermore National Lab, USA) has discussed how several aspects of existing continuum damage models can be tested during early operation of X-FEL at lower X-ray energies in the range of 0.8-5 keV and low fluences, focusing particularly on macroscopic collective effects such as particle charging, expansion, and average ionization of nanospheres. For more information, see the paper, "Modeling of the damage dynamics of nanospheres exposed to x-ray free-electron-laser radiation", S. P. Hau-Riege et al., Phys. Rev. E77, 041902 (2008).