Werellapatha Kalpani, Escanhoela Carlos A, Fabbris Gilberto, Haskel Daniel, Ankudinov Alexei, Chow Paul
Department of Physics and Astronomy, University of Maine, Orono, ME 04469, United States of America.
J Phys Condens Matter. 2019 Jun 26;31(25):255301. doi: 10.1088/1361-648X/ab111d. Epub 2019 Mar 19.
We present a study of electronic and magnetic properties of nominal magnetite nanoparticles (NPs) (~6 nm) at high pressure in the presence of silicon pressure medium using x-ray absorption near edge structure (XANES), x-ray magnetic circular dichroism (XMCD) and non-resonant x-ray emission spectroscopy (XES). XANES data show a reduction of Fe charge state, a change in local environment around Fe at tetrahedral sites, and a reduced occupation of Fe 4p orbitals, not seen in previous pressure studies of bulk magnetite. XMCD data show a continuous magnetic moment reduction of ~50% between ambient pressure and 20 GPa, similar to what was observed in previous bulk magnetite studies. XES spectra of NPs indicate a gradual change in spin configuration away from the high-spin state consistent with a postulated charge transfer from Fe 4p to 3d states and the observed reduction in XMCD signal. Taken together, the results point to substantial differences in the response of electronic and magnetic properties of the nano-counterparts of bulk magnetite at high pressure.
我们展示了一项在高压下，使用x射线吸收近边结构（XANES）、x射线磁圆二色性（XMCD）和非共振x射线发射光谱（XES），对名义上的磁铁矿纳米颗粒（NPs）（~6纳米）在硅压力介质存在下的电子和磁性性质的研究。XANES数据显示Fe电荷态降低、四面体位置周围Fe的局部环境发生变化以及Fe 4p轨道的占据减少，这在之前对块状磁铁矿的压力研究中未见。XMCD数据显示在环境压力和20 GPa之间磁矩持续降低约50%，这与之前块状磁铁矿研究中观察到的情况类似。NPs的XES光谱表明自旋构型逐渐从高自旋态转变，这与假定的从Fe 4p到3d态的电荷转移以及观察到的XMCD信号降低一致。综合来看，结果表明块状磁铁矿的纳米对应物在高压下电子和磁性性质的响应存在显著差异。
