Exploiting Synergies between Thin Films and Bulk Materials: the Key to Understanding Magnetic Properties and Magneto-Transport in MnAl

具有高磁晶各向异性的磁性材料需要薄膜和块体两种形式，以用于各种应用，包括紧急自旋电子器件、计算机存储介质、混合动力汽车的电机和风力涡轮机的发电机。除了具有高的磁晶各向异性外，MnAl最近还表现出了新的磁输运效应。这些方面，再加上该材料不含稀土元素，原材料成本低，使MnAl对上述应用具有极大的吸引力。到目前为止生产的MnAl材料通常表现出某些但不是所有所需磁性能的极佳值。例如，在MnAl薄膜中，已经报道了高矫直力和低饱和磁化强度，这两者都是自旋电子器件所需要的，但对(各向异性)磁阻却知之甚少。在块体材料中，已经报道了高的饱和磁化强度，但矫顽力明显低于薄膜材料。高的矫直力和磁化是永磁体的关键。由于对MnAl薄膜的微观结构还没有研究，而且块体MnAl中的微观结构细节还在不断涌现，导致这种材料不同形式磁性能差异的机制还不清楚。对某些掺杂元素对块体MnAl磁性能的影响进行了初步探讨，但要弄清其影响还需要进一步的工作。对掺杂的MnAl薄膜的研究还很少。解决这些问题是生产具有磁性的MnAl材料的关键步骤，这些材料适用于自旋电子学和永磁体的应用。薄膜和块体材料的开发通常是分开进行的，但在这个项目中，将利用薄膜和块体材料之间的协同作用，以便在理解MnAl的磁性和掺杂的影响方面取得快速进展。例如，通过分析高矫顽力的MnAl薄膜，并将其微结构与MnAl块体材料的微观结构进行比较，将阐明高矫直力所需的条件。将开发新的加工路线，在散装材料中重现这些条件。掺杂元素的溶解度和相平衡将在块状材料中研究，利用的优势是，与薄膜不同，不存在可能影响结果的衬底。从块体中获得的知识将被转移，以加速掺杂薄膜的成功制备。将详细研究所生产材料的磁性和磁传输特性，以阐明控制机制并评估其应用的适宜性。

Magnetic materials with high magneotcrystalline anisotropy are required in both thin film and bulk forms for a wide spectrum of applications including emergent spintronic devices, computer storage media, motors for hybrid vehicles and generators for wind turbines. In addition to a high magnetocrstalline anisotropy, MnAl has recently been shown to exhibit novel magneto-transport effects. These aspects, combined with the fact that the material contains no rare earth elements and has low raw materials costs, make MnAl highly attractive for the applications mentioned above. The MnAl materials produced to date typically exhibit excellent values of some but not all the required magnetic properties. For example in thin films of MnAl, high coercivity with low saturation magnetisation has been reported, both of which are required in spintronic devices, but little is known about the (anisotropic) magnetoresistance. In bulk materials, high values of saturation magnetisation have been reported but the coercivity is significantly lower than that reported in thin films. High coercivity and magnetisation are crucial for permanent magnets. As the microstructure of MnAl thin films has not been studied and details of the microstructure in bulk MnAl are still emerging, the mechanisms leading to the contrasting magnetic properties in different forms of this material are not understood. The influence of some doping elements on the magnetic properties of bulk MnAl has been tentatively explored but much further work is required to clarify the effects. Very few studies have been carried out on doped MnAl films. Solving these problems is the key step which will allow the production of MnAl materials with magnetic properties tailored to applications in spintronics and permanent magnets.The development of thin films and bulk materials often takes place separately but in this project, synergies between thin films and bulk materials will be exploited in order to progress rapidly in understanding the magnetic properties and the effect of doping in MnAl. For example, by analysing highly coercive MnAl thin films and comparing their microstructure with that of MnAl bulk materials, the conditions necessary for high coercivity will be elucidated. Novel processing routes will be developed which reproduce these conditions in bulk materials. The solubility of the doping elements and phase equilibria will be studied in bulk materials, using the advantage that, unlike in thin films, no substrate is present which could influence the results. The knowledge gained from bulk will be transferred in order to accelerate the successful fabrication of doped films. The magnetic and magneto-transport properties of the materials produced will be studied in detail in order to elucidate the controlling mechanisms and assess their suitability for application.