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

B2 合金薄膜中无序诱导铁磁性的微观理解 II (MUMAGI II)

• 批准号: 322462997
• 负责人: Dr. Rantej Bali, Ph.D.
• 金额: --
• 依托单位: School of Computer Science
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/322462997?language=en
• 关键词: Microscopic; understanding; disorder; induced; ferromagnetism

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.

对微小结构变化敏感的磁相变可以用来直接探测磁有序和原子排列之间的相关性。在材料中，这种转变可以在空间上受到限制，有额外的可能性，以调查在空间限制的界面处的磁行为。上述机会存在于化学有序的B2相的某些合金中，其可以无序到A2相。在顺磁性B2-Fe 60 Al 40和反铁磁性B2-Fe 50 Rh 50中，Fe位分别与Al或Rh位的细微切换足以引起大的铁磁饱和磁化强度。感应磁化强度已被归因于增加Fe-Fe最近邻相互作用。这种无序感生铁磁性现象已经被人们知道了几十年，但是它的研究主要局限于大块材料。其确切的机制仍然存在疑问，例如，晶格参数随无序的变化已经被观察到，但它对感生磁化强度的贡献还没有得到澄清。此外，在局部无序区的界面处的磁结构是不清楚的。我们将使用光离子辐照（如Ne+）作为一种有效的工具来系统地无序薄膜材料来解决这些问题。此外，离子束可以聚焦到nm尺寸，用于产生铁磁纳米结构和有序/无序（B2/A2）相边界。在拟议的36个月期间，与两名博士生的资源，我们将部署离子辐照，以调查无序诱导铁磁性沿着两个交织的方法：在HZDR，我们将调查的界面离子诱导铁磁性区域的特征，其磁阻特性。偶极场的铁磁A2结构将被调查作为一种手段，影响参数，如磁化率和周围的B2有序材料的转变温度。在UDE系统无序薄膜的B2 -Fe 60 Al 40和-Fe 50 Rh 50和跟踪其磁性和结构的变化，使用X射线和穆斯堡尔谱，从而实现了微观理解的影响原子重排的铁磁性出现分别从顺磁性和反铁磁性前体。本研究将为进一步研究无序诱导铁磁性材料的机制和界面效应奠定基础。