Microscopic understanding of disorder induced ferromagnetism in B2-alloy thin films II (MUMAGI II)

对微小结构变化敏感的磁相变可以用来直接探测磁有序与原子排列之间的关系。在这种跃迁可以被空间限制的材料中，有额外的可能性来研究空间限制界面处的磁性行为。上述机会存在于某些化学有序的B2相合金中，这些合金可以无序地变成A2相。在顺磁性的B2-Fe60Al40和反铁磁性的B2-Fe50Rh50中，Fe位分别与Al或Rh位的细微切换足以产生较大的铁磁饱和磁化。感应磁化归因于Fe-Fe最近邻相互作用的增加。这种无序引起的铁磁性现象已经被发现了几十年；然而，它的调查在很大程度上仅限于散装材料。其精确机理仍有疑问，例如，观察到晶格参数随无序变化，但其对诱导磁化的贡献尚未阐明。此外，局部失序区界面处的磁性结构尚不清楚。我们将使用光离子辐照（例如Ne+）作为系统地对薄膜材料进行无序化的有效工具来解决这些问题。此外，离子束可以聚焦到纳米尺度，以产生铁磁性纳米结构和有序/无序（B2/A2）相边界。在计划的36个月期间，我们将利用两名博士生的资源，沿着两种相互交织的方法部署离子辐照来研究无序诱导铁磁性：在HZDR，我们将通过表征其磁阻特性来研究离子诱导铁磁性区域的界面。将研究铁磁a2结构的偶极场，作为影响周围b2有序材料的磁化率和转变温度等参数的手段。在UDE上系统地对B2 -Fe60Al40和-Fe50Rh50薄膜进行了无序化，并利用x射线和Mössbauer光谱跟踪了它们的磁性和结构变化，从而从微观上了解了原子重排对顺磁性和反铁磁性前体分别产生的铁磁性的影响。本项目将为今后研究无序诱导铁磁性材料的机制和界面效应奠定基础。

Magnetic phase transitions that are sensitive to small structural variations can be used to directly probe the correlation between magnetic ordering and the atomic arrangement. In materials where such transitions can be spatially confined, there is the additional possibility to investigate the magnetic behaviour at the interfaces of the spatial confinement. The above opportunities exist in certain alloys of the chemically ordered B2 phase that can be disordered to the A2 phase. In paramagnetic B2-Fe60Al40 and in antiferromagnetic B2-Fe50Rh50, subtle switching of the Fe site with the Al or Rh sites respectively is sufficient to induce a large ferromagnetic saturation magnetization. The induced magnetization has been attributed to increased Fe-Fe nearest-neighbour interactions. This phenomenon of disorder induced ferromagnetism has been known for several decades; however its investigations have largely been restricted to bulk materials. There still remain open questions on its precise mechanism, for example, a change in the lattice parameter with disorder has been observed, however its contribution to the induced magnetization has not been clarified. Furthermore, the magnetic structure at the interfaces of locally disorder regions is unclear. We will approach these problems using light ion-irradiation (e.g. Ne+) as an effective tool to systematically disorder thin film materials. Furthermore, ion-beams can be focused to nm dimensions for generating ferromagnetic nanostructures and order/disorder (B2/A2) phase boundaries. In the proposed 36-month period, with the resource of two PhD students, we will deploy ion-irradiation to investigate disorder induced ferromagnetism along two intertwined approaches: at the HZDR, we will investigate the interfaces of ion-induced ferromagnetic regions by characterizing their magneto-resistive properties. Dipolar fields of the ferromagnetic A2-structures will be investigated as a means to influence parameters such as susceptibility and transition temperature of the surrounding B2-ordered material. At the UDE systematically disordered thin films of B2 -Fe60Al40 and -Fe50Rh50 and track their magnetic and structural changes using X-ray and Mössbauer spectroscopy, thereby achieving a microscopic understanding of the effect of atomic rearrangements on ferromagnetism emerging respectively from paramagnetic and antiferromagnetic precursors. This project will lay the foundation for future investigations on the mechanisms and interface effects in materials exhibiting disorder induced ferromagnetism.