用X射线吸收近边光谱研究富铂FePt/Fe3O4异质二聚体的热演化
Thermal evolution of Pt-rich FePt/Fe3O4 heterodimers studied using x-ray absorption near edge spectroscopy
摘要：
FePt/Fe 3 O 4纳米颗粒可以用作构建块，在热退火时，获得具有组合磁性的磁性纳米复合材料。虽然退火前和退火后的样品通常具有良好的特性，但在退火过程中进行详细的调查是必要的，以揭示中间过程的作用，以产生理想的复合材料。我们提出了一种替代的方法，使用原位XANES研究的热演化的油酸和油胺涂层的富铂FePt/Fe 3 O 4异二聚体。随着温度的升高，在表面活性剂的作用下，Fe_3O_4逐渐还原为FeO，而在550 K以上开始生成Fe_3Pt。在840 K时，FeO的突然增加进一步驱动相变以稳定铁铂软相。因此，Fe 3 O 4还原作为催化剂，促进富Pt FePt和Fe 3 O 4/FeO之间的Fe和Pt相互扩散，形成Fe 3 Pt，而不是具有硬磁性能的交换耦合FePt/Fe 3 O 4。此外，异二聚体末端的界面的作用进行了讨论。对退火前后的样品进行了TEM、XRD、EXAFS、磁强计和穆斯堡尔谱等表征。
英文摘要：
FePt/Fe3O4 nanoparticles can be used as building blocks to obtain, upon thermal annealing, magnetic nanocomposites with combined magnetic properties. Although the pre- and post-annealed samples are usually well characterized, a detailed investigation during annealing is necessary to reveal the role of intermediate processes to produce a desirable composite. We present an alternative method using in situ XANES to investigate the thermal evolution of oleic acid and oleylamine coated Pt-rich FePt/Fe3O4 heterodimers. As the temperature increases, a progressive reduction of Fe3O4 to FeO occurs helped by the thermolysis of the surfactants; while above 550 K Fe3Pt starts to be formed. At 840 K an abrupt increase of FeO further drives the phase transformation to stabilize the iron platinum soft phase. Thus, the Fe3O4 reduction acts as catalyst that promotes the Fe and Pt interdiffusion between the Pt-rich FePt and Fe3O4/FeO to form Fe3Pt instead of exchange coupled FePt/Fe3O4 with hard magnetic properties. In addition, the role of the interface of the heterodimer ends is discussed. The pre- and post-annealed samples were also characterized by TEM, XRD, EXAFS, magnetometry and Mössbauer spectroscopy.
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