Half-metallic ferromagnets: materials fundamentals for next-generation spintronics

半金属铁磁体：下一代自旋电子学的材料基础

• 批准号: EP/K03278X/1
• 负责人: Vlado Lazarov
• 金额: $ 72.48万
• 依托单位: University of York
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FK03278X%2F1
• 关键词: Half; metallic; ferromagnets; materials; fundamentals

Semiconductors (such as silicon) underpin so many aspects of modern life, through electronics and data processing for the WWW, telecoms, medicine, transport, etc., that it is hard to overstate their importance. However, silicon chip technology is approaching hard physical limits and alternatives are needed. One radical approach is spintronics, where the both the "spin" and charge of electrons are used for data storage and processing. Spin is a fundamental property of electrons related to magnetism: in a magnetic field, a spin prefers to align in one of two ways, along or against the field. Full utilisation of spin would enable revolutionary new chip designs, which are fast, energy-efficient and fully integrate data storage with logic. We will study half-metallic ferromagnetic (HMF) materials. HMFs are a class of materials discovered theoretically in the 1980s which combine the properties of a semiconductor and a ferromagnetic metal. Only one of the two electron spin alignments can easily move inside an HMF - they are "100% spin-polarised". They should hence be ideal materials for use in spintronics. However, despite major research efforts to make HMF devices, in most cases HMFs do not outperform ordinary magnetic materials (which are typically 30-40% spin-polarised). There is no clear understanding of why this is the case, which prevents the potential of HMFs being unlocked for advanced spintronics. We propose to solve this outstanding problem with a comprehensive and rigorous study of HMFs in the physical form which is actually used in devices, i.e. in thin-films on an oxide or semiconductor substrate. We will combine our expertise in four areas: (1) production of high quality thin films of HMFs, (2) characterisation of magnetic thin films down to the atomic level, (3) accurate theoretical description of these materials, and (4) fabrication of HMF spintronic devices. This will enable us to study holistically the most likely culprits for weakened HMF performance, namely temperature, defects and the HMF /substrate interface. Spin-polarisation collapses as an HMF heats up, and this cut-off, for a practical device, must be well above room temperature. We will measure this explicitly and model it with state-of-the-art theory developed recently in Warwick. Residual defects in the thin films can destroy spin polarisation and we will both understand these via atomic-scale imaging / modelling and adjust our thin film growth to minimise them. Finally, there must always be an interface between the HMF and its substrate, which also influences the spin polarisation and functional performance. We will image and model the interfaces, and again adjust our growth to optimise them. Atomic-scale imaging and analysis is possible using cutting-edge aberration-corrected electron microscopes (York and Warwick each have such a microscope, with complementary capabilities). Finally, this fundamental work will be correlated with the functional performance of the HMFs in prototypical spintronic devices. We will be able to fabricate devices, using established designs, and subsequently measure the atomic-scale interfaces and defects on the actual device structure. This unique combination of capabilities ranging from first-principles theory to device performance will enable the first comprehensive and rigorous study of half-metallicity in real thin film structures. Our goals are to understand in a fundamental way the limitations of HMFs in real structures, to guide future HMF device design, and also develop the highest possible room temperature spin polarisation in HMF thin films. Between York and Warwick, we have growth expertise in three different classes of HMF material (transition metal pnictides, magnetite and Heusler alloys) which will enable us both to produce a generalised understanding of HMFs and find the best materials for ultra-high spin polarisation films.

半导体（如硅）在现代生活的许多方面都发挥着重要作用，通过电子设备和万维网、电信、医药、交通等领域的数据处理，其重要性怎么强调都不为过。然而，硅芯片技术正在接近硬物理极限，需要替代品。一种激进的方法是自旋电子学，其中电子的“自旋”和电荷都用于数据存储和处理。自旋是与磁性有关的电子的基本属性：在磁场中，自旋倾向于以两种方式中的一种排列，沿场或反场。充分利用自旋将实现革命性的新芯片设计，这些芯片快速，节能，并将数据存储与逻辑完全集成。我们将研究半金属铁磁（HMF）材料。HMFs是20世纪80年代从理论上发现的一类材料，它结合了半导体和铁磁性金属的特性。两种电子自旋排列中只有一种能在HMF内轻松移动——它们是“100%自旋极化”的。因此，它们应该是用于自旋电子学的理想材料。然而，尽管在制造HMF器件方面进行了大量的研究，但在大多数情况下，HMF的性能并不优于普通磁性材料（通常为30-40%的自旋极化）。目前还不清楚为什么会出现这种情况，这阻碍了HMFs的潜力被释放出来用于先进的自旋电子学。我们建议通过对实际用于器件的物理形式的HMFs进行全面和严格的研究来解决这个突出的问题，即在氧化物或半导体衬底上的薄膜。我们将结合我们在四个领域的专业知识：(1)生产高质量的HMF薄膜，(2)磁性薄膜的表征低至原子水平，(3)这些材料的准确理论描述，以及(4)制造HMF自旋电子器件。这将使我们能够从整体上研究HMF性能减弱的最可能的罪魁祸首，即温度、缺陷和HMF /衬底界面。当HMF升温时，自旋极化就会崩溃，而对于一个实用的装置来说，这个截止温度必须远高于室温。我们将明确地测量它并用华威大学最近开发的最先进的理论来模拟它。薄膜中的残余缺陷会破坏自旋极化，我们将通过原子尺度成像/建模来理解这些缺陷，并调整薄膜的生长以最小化它们。最后，HMF与其衬底之间必须始终存在一个界面，这也会影响自旋极化和功能性能。我们将对界面进行成像和建模，并再次调整我们的增长以优化它们。原子尺度的成像和分析可以使用先进的像差校正电子显微镜（约克和沃里克都有这样的显微镜，具有互补的能力）。最后，这项基础工作将与原型自旋电子器件中HMFs的功能性能相关联。我们将能够制造设备，使用既定的设计，并随后测量原子尺度的界面和实际设备结构上的缺陷。这种从第一性原理理论到器件性能的独特能力组合将使真正薄膜结构中半金属性的首次全面和严格的研究成为可能。我们的目标是从根本上了解HMF在实际结构中的局限性，指导未来的HMF器件设计，并在HMF薄膜中开发尽可能高的室温自旋极化。在约克和沃里克之间，我们在三种不同类别的HMF材料（过渡金属镍，磁铁矿和Heusler合金）方面拥有专业知识，这将使我们都能够对HMF产生一般的理解，并找到超高自旋极化膜的最佳材料。

项目成果

Correlation between spin transport signal and Heusler/semiconductor interface quality in lateral spin-valve devices

横向自旋阀器件中自旋输运信号与 Heusler/半导体界面质量之间的相关性

• DOI: 10.1103/physrevb.98.115304
• 发表时间: 2018
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Achinuq B

Enhanced magnetoelectric effect in M-type hexaferrites by Co substitution into trigonal bi-pyramidal sites

• DOI: 10.1063/1.5017683
• 发表时间: 2018-02-19
• 期刊: APPLIED PHYSICS LETTERS
• 影响因子: 4
• 作者: Beevers, J. E.;Love, C. J.;Dhesi, S. S.
• 通讯作者: Dhesi, S. S.

Correlated electron diffraction and energy-dispersive X-ray for automated microstructure analysis

用于自动微观结构分析的相关电子衍射和能量色散 X 射线

• DOI: 10.1016/j.commatsci.2023.112336
• 发表时间: 2023
• 期刊: Computational Materials Science
• 影响因子: 3.3
• 作者: Duran E

Spin pumping in magnetic trilayer structures with an MgO barrier.

• DOI: 10.1038/srep35582
• 发表时间: 2016-10-18
• 期刊: Scientific reports
• 影响因子: 4.6
• 作者: Baker AA;Figueroa AI;Pingstone D;Lazarov VK;van der Laan G;Hesjedal T
• 通讯作者: Hesjedal T

Direct band-gap measurement on epitaxial Co2FeAl0.5Si0.5 Heusler-alloy films

• DOI: 10.1063/1.4916817
• 发表时间: 2015-05-07
• 期刊: JOURNAL OF APPLIED PHYSICS
• 影响因子: 3.2
• 作者: Alhuwaymel, Tariq F.;Carpenter, Robert;Hirohata, Atsufumi
• 通讯作者: Hirohata, Atsufumi