Spin-selective XAFS: a noble analytical method for magnetic nano-particles

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This project aims to establish spin-selective XAFS spectroscopy as a method of characterizing the magnetic and electronic structure of magnetic nano-particles. Here it is necessary to develop high-resolution x-ray spectrometers with large acceptance in order to measure generally weak Kβ-emissions of 3d elements.In 2005, our own dispersive-type spectrometer was modified for detecting Kβ-emissions, and was utilized for observing resonant inelastic x-ray scattering (RIXS) of several standard materials to deduce their spin-selective XAFS. Through these measurements, it has been achieved to ultimately suppress lifetime-broadenings, and to obtain polarized spin-selective XAFS for single-crystal of LaMnO_3. On the other hand, it has been found that magnetic nano-particles are unstable for incident x-rays produced by synchrotron sources. The instability made it difficult to precisely obtain the spin-selective XAFS of the particles.Thus, in 2006, a focusing-type spectrometer was made by rebuilding the dispersive-type spectrometer, and was named as 'Peacock' after its shape. By using the 'Peacock', lifetime-broadening-suppressed XAFS spectra of CuO nano-particles on ZnO with various Cu concentrations up to as low as 1 mol% were obtained from their RIXS. Similar experiments for a basic high-Tc system, La_<2-x>Sr_xCuO_4 (LSCO) reveal that 1s-3d excitation of LSCO is very sensitive Sr-concentration and polarization. After these preliminary studies to demonstrate the high-sensitivity of 'Peacock', spin-selective XAFS spectra of magnetic nano-materials of several Fe oxides were measured within fairly short periods. Here almost no radiation-damage was distinguishable. Based on the data obtained, papers are now in preparation.