Tailoring magnetic properties of Mn-Cr chalcogenide alloys and heterostructures

我们将开发由过渡金属元素(铬、锰)和第VI族元素(S、硒、碲)组成的新型薄层材料；这些鲜为人知的材料有望满足广泛的自旋相关电子(自旋电子学)器件的要求。这项建议的目的是在制造和研究这一系列具有必要成分和晶体质量的单层和多层材料方面迈出第一步，但我们也将在项目的时间表内制造和研究选定的演示设备。“自旋电子学”一词涵盖了许多拟议的设备(例如，但不限于传感器、存储元件、二极管和晶体管)，在这些设备中，电子的自旋被操纵，以感知、存储、携带或处理信息。换句话说，这些设备利用了电子的固有磁性以及它们的电荷，因此可以在能源效率、速度或尺寸方面提供改进。实现这种设备的奖品是巨大的；例如，硬盘读取头核心设备(可归类为自旋电子学设备)的惊人商业成功激发了极大的兴奋和针对自旋的更广泛应用的紧张研究工作。尽管如此，事实证明，从早期理论预测确定的最初几种候选材料中生产出工业用途的磁性半导体是不可能的。因此，全世界自旋电子界的许多团体现在都在扩大所考虑的材料的范围，以及可以利用的磁性行为的类型；这种探索重新振兴了整个自旋电子学领域。这项建议涉及一种候选材料家族，该家族已在理论文献中提出，但(除我们的试验外)尚未在实验室产生。(Cr，Mn)(S，Se，Te)材料系列满足几个关键要求。首先，这些化合物的薄层将在工业标准的GaAs衬底上生长，并将采用与衬底相同的晶体结构。这使得得到的结构与现有的半导体技术高度兼容。其次，我们的初步研究和几个小组的理论研究表明，我们将能够通过调整组成来产生所有潜在有用的类型的磁行为。它们包括铁磁体和半金属(其中过渡金属的磁矩彼此平行并相加)、反铁磁体(它们相反地对齐并抵消)和亚铁磁体(不同的过渡金属相反地对齐但不等价，因此不能精确地抵消)。在不同类型的自旋电子器件中，上述任何磁性类型的层都可以形成有源层。第三，这些材料在化学和结构上与我们可以作为多层结构的一部分生长的非磁性半导体(例如，ZnSe，MGS)兼容；这些材料允许形成必要的电接触和电势垒。我们的计划将涉及大量的努力，以生长这些新材料，以获得高质量的层状晶体；初步工作表明，成功将不存在根本障碍。将对材料的结构、磁性和电学性质进行研究，以确定最有希望的成分和基于这些成分的最合适的靶器件设计。然后将生产演示设备，以测试材料在现实设备环境中的表现，并提高人们对工作的兴趣。这项工作需要广泛的经验基础，因此我们组建了一支在分子束外延生长、电子设备制造和测量、磁光光谱和磁测量方面拥有专业知识的团队。

We shall develop new, thin-layer materials composed of transition metal elements (Cr, Mn) combined with group VI elements (S, Se,Te); these little-known materials offer the prospect of satisfying the requirements for a wide range of spin-dependent electronic ("spintronic") devices. This proposal aims to take the first steps in making and investigating single- and multi-layer materials from this family with the necessary compositions and crystal quality, but we shall also manufacture and study selected demonstrator devices within the timescale of the project. The term "spintronics" encompasses many proposed devices (for example, but not exclusively, sensors, memory elements, diodes and transistors) in which it is the spin of the electrons that is manipulated in order to sense, store, carry or process information. In other words, these devices exploit the intrinsic magnetic properties of electrons as well as their charge and, as a result, may offer improvements in energy efficiency, speed or size. The prizes for the realization of such devices are enormous; for example, the phenomenal commercial success of the device at the heart of hard disk read heads (which can be classed as a spintronic device) has stimulated great excitement and intense research efforts aiming at wider applications of spin. Despite this, it has not proved possible to produce industrially-useful magnetic semiconductors from the first few candidate materials identified by early theoretical predictions. As a result, many groups in the worldwide spintronics community are now engaged in widening both the scope of the materials considered, and the types of magnetic behaviour that can be exploited; this search has revitalised the whole field of spintronics. This proposal addresses a candidate material family that has been proposed in the theoretical literature but (apart from our trials) has not yet been produced in the laboratory. The (Cr, Mn)(S,Se,Te) material family satisfies several crucial requirements. Firstly, thin layers of these compounds will be grown on industry standard GaAs substrates and will adopt the same crystal structure as the substrate. This makes the resulting structures highly compatible with existing semiconductor technologies. Secondly, preliminary studies of ours and theoretical studies of several groups imply that we will be able to produce all the potentially useful types of magnetic behaviour by tuning the composition. These include ferromagnets and half-metals (where the transition metal magnetic moments align parallel to each other and add), antiferromagnets (where they align oppositely and cancel) and ferrimagnets (where dissimilar transition metals align oppositely but are not equivalent and so cannot exactly cancel). Layers of any of the above magnetic types can form the active layer in different types of spintronic devices. Thirdly, these materials are chemically and structurally compatible with non-magnetic semiconductors (e.g, ZnSe, MgS) that we can grow as parts of multi-layer structures; these allow the necessary electrical contacts and electrical barriers to be formed. Our programme will involve a substantial effort in growing these new materials to obtain layers of high crystal quality; preliminary work indicates that there will be no fundamental obstacles to success. The structural, magnetic and electrical properties of the materials will be investigated to identify the most promising compositions and most appropriate target device designs based on them. Demonstrator devices will then be produced to test how the materials perform in realistic device contexts and to promote interest in the work. This work requires a broad base of experience and so we have formed a team having expertise in MBE growth, electrical device fabrication and measurement, magneto-optical spectroscopy and magnetometry.