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

本项目旨在建立自旋选择XAFS光谱，作为表征磁性纳米粒子的磁性和电子结构的一种方法。在这里，为了测量3D元素的一般弱Kβ发射，有必要开发具有较大接受度的高分辨率X射线能谱仪。2005年，我们自己的色散型能谱仪被改装用于检测Kβ发射，并被用来观测几种标准材料的共振非弹性X射线散射，推导出它们的自旋选择性XAFs。通过这些测量，已经实现了最终抑制寿命展宽，并获得了LaMnO_3单晶的极化自旋选择XAFS。另一方面，发现磁性纳米粒子对同步辐射产生的入射X射线是不稳定的。这种不稳定性使得精确获得粒子的自旋选择XAFS变得困难，因此，在2006年，通过对色散型光谱仪的改造，制成了聚焦式光谱仪，并根据其形状命名为孔雀。利用孔雀的RIXS，获得了不同铜含量的CuO纳米粒子在氧化锌表面的寿命展宽抑制XAFS谱。对一个基本的高T_c体系La_&lt；2-x&Gt；Sr_xCuO_4(LSCO)的类似实验表明，LSCO的1S-3D激发对锶的浓度和极化非常敏感。为了证明“孔雀”的高灵敏度，我们在较短的时间内测量了几种铁氧化物磁性纳米材料的自旋选择XAFS谱。在这里，几乎没有明显的辐射损害。根据获得的数据，论文现在正在准备中。

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.