Dresden 2003 – wissenschaftliches Programm

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MA: Magnetismus

MA 14: Poster: Schichten(1-31), Spinabh.Trsp.(32-47), Exch.Bias(48-54), Spindyn.(55-64), Mikromag.(65-76), Partikel(77-88), Oflmag.(89-92), Spinelektr.(93-98), Elektr.Theo.(99-103), Mikromag+PhasÜ+Aniso.(104-122), MagnMat.(123-134), Messm+Mol-Mag.(135-139), Kondo(140-151)

MA 14.135: Poster

Dienstag, 25. März 2003, 15:15–19:15, Zelt

Digital Lock-In technique for hard X-ray circular dichroism experiments — •Frank Weigand and Eberhard Goering — Max-Planck-Insitut für Metallforschung, 70569 Stuttgart

In a conventional X-ray circular dichroism experiment (XMCD), which measures element selective the spin- and orbital polarization, the magnetization of the sample is flipped parallel and antiparallel to the direction of the fixed circular polarized synchrotron light. In the hard X-ray regime it is possible to switch the helicity by a single crystal quarter wave plate. We have developed a pure digital lock-in technology, which utilizes the change in circular polarization of synchrotron radiation of transmitted light by a phase retarding diamond single crystal in the vicinity of a Bragg reflection. It is necessary to achieve a perfectly centered quarter wave plate Bragg condition at each energy point to acchieve a high quality XMCD experiment. This has been reached by a digital Lock-In Piezo driven position controller, which flips the diamond crystal at about 10Hz between left and right circular polarized transmitted light and a standard deviation to the optimal position of less than 1/50000 degree. A signal-to-noise ratio quite near to photon statistics was reached at the Pt L3 edge of a standard PtFe-sample.