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颗粒的磁性和电子结构的方法。2005年，我们对自己研制的色散型X射线谱仪进行了改进，使之能够探测Kβ发射，并利用该谱仪对几种标准物质的共振非弹性X射线散射（RIXS）进行了观测，推导了它们的自旋选择XAFS。通过这些测量，最终实现了对LaMnO_3单晶寿命展宽的抑制，并获得了极化自旋选择XAFS谱。另一方面，已经发现磁性纳米颗粒对于由同步加速器源产生的入射X射线是不稳定的。这种不稳定性使得很难精确地获得粒子的自旋选择XAFS，因此在2006年，通过对色散型光谱仪进行改造，制成了聚焦型光谱仪，并以其形状命名为“孔雀”。通过使用“量子点”，从其RIXS获得了ZnO上CuO纳米颗粒的不同Cu浓度（低至1mol%）的寿命展宽抑制XAFS谱。对一个基本的高Tc体系La_<2-x>Sr_xCuO_4（LSCO）的类似实验表明，LSCO的1 s-3d激发对Sr浓度和极化非常敏感。在这些初步的研究，以证明高灵敏度的“磁锁”，自旋选择性XAFS光谱的磁性纳米材料的几个铁氧化物在相当短的时间内测量。这里几乎看不出辐射损伤。目前正在根据所获得的数据编写文件。

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.