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在薄膜和块状两种形式中被广泛应用，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。除了高的磁晶各向异性外，MnAl最近还显示出新颖的磁输运效应。这些方面，结合材料不含稀土元素和具有低原材料成本的事实，使得MnAl对于上述应用非常有吸引力。迄今为止生产的MnAl材料通常表现出一些但不是所有所需磁性能的优异值。例如，在MnAl薄膜中，已经报道了具有低饱和磁化强度的高磁致伸缩性，这两者都是自旋电子器件中所需要的，但对（各向异性）磁阻知之甚少。在散装材料，高值的饱和磁化强度已被报道，但矫顽力是显着低于薄膜报道。高矫顽力和磁化强度对永磁体至关重要。由于MnAl薄膜的微观结构尚未研究，并且块状MnAl中的微观结构的细节仍在出现，因此导致这种材料的不同形式的对比磁性能的机制尚不清楚。一些掺杂元素对块状MnAl的磁性能的影响已被初步探索，但需要进一步的工作来澄清的效果。对掺杂的MnAl薄膜的研究很少。解决这些问题是关键的一步，这将允许生产MnAl材料的磁性能定制的应用在自旋电子学和永磁体。薄膜和块体材料的开发往往单独进行，但在这个项目中，薄膜和块体材料之间的协同作用将被利用，以了解磁性能和MnAl掺杂的影响迅速进步。例如，通过分析高矫顽性MnAl薄膜，并将它们的显微结构与MnAl块体材料的显微结构进行比较，将阐明高矫顽性所需的条件。将开发新的工艺路线，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进行研究，利用的优点是，与薄膜不同，不存在可能影响结果的基底。从本体获得的知识将被转移，以加速掺杂薄膜的成功制造。将详细研究所产生的材料的磁性和磁输运性质，以阐明控制机制并评估其适用性。

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.