Dynamical investigation of tunable magnetism in Au@Ni-carbide nanocrystals by a combined soft and hard X-ray adsorption spectroscopy
Dynamical investigation of tunable magnetism in Au@Ni-carbide nanocrystals by a combined soft and hard X-ray adsorption spectroscopy
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结合软硬X射线吸收光谱对Au@Ni-碳化物纳米晶中可调磁性的动态研究
DOI：
10.1007/s12274-021-4005-8
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通讯作者：
Lin Guo
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作者：
Weifeng Huang;Jianxin Kang;Tingwen Chen;Dawei Pang;Lihua Wang;Huang Wei;Changchun Yang;Dongfeng Zhang;Lin Guo
镍基磁性纳米晶在磁性和催化装置中有着广泛的应用。通过非磁性掺杂或相变可以容易地获得镍的可调谐磁性。然而，由于六方密排Ni（hcp-Ni）和Ni 3C具有相似的原子结构，因此人们常常把Ni的磁调节效应从面心立方（fcc）到六方密排（hcp）的相变与Ni 3C相混淆。在这里，我们提出了一系列的Au@ Ni-碳化物磁性材料，从控制碳酸化的Au@Ni核壳结构，其磁性是可调的，通过调整在Ni层中的碳的量。非原位硬X射线吸收光谱（XAS）在金属K边和软X射线吸收光谱在金属L边和碳K边提供了坚实的证据从fcc-Ni到NixC的碳酸化过程，而不是向hcp-Ni的相变。进一步的研究表明，杂化材料的磁性主要来自于残余的fcc-Ni。这一结果为区分六方相Ni_3C和六方相Ni提供了一种准确有效的方法，也为实际应用中控制Ni基材料的磁性提供了途径。
Nickel based magnetic nanocrystals have been widely applied in magnetic and catalytic facilities. Tunable magnetic properties of nickel can be easily obtained via non-magnetic doping or phase transformation. However, phase transformation from face centered cubic (fcc) to hexagonal close packed (hcp) induced magnetism adjustment of Ni are always confused with nickel carbide (Ni3C), due to the similar atomic structures of hcp-Ni and Ni3C. Here, we present series of Au@Ni-carbide magnetic materials achieved from the controlled carbonation of Au@Ni core-shell structures, whose magnetism is tunable by adjusting the amount of carbon in the Ni layer. Ex-situ hard X-ray absorption spectroscopy (XAS) at the metal K edge and soft XAS at both metal L edge and carbon K edge provide solid evidence for the carbonation process from fcc-Ni to NixC, rather than phase transformation to hcp-Ni. Further investigation reveals that the magnetism of the hybrids is mainly contributed from the residual fcc-Ni. The result represents an accurate and effective way to distinguish hexagonal Ni3C from hcp-Ni, and provides the pathway to control magnetism of Ni-based materials for applications.