Efficient spin voltage/current generation in a ferromagnet/semiconductor lateral spin-valve

铁磁体/半导体横向自旋阀中高效产生自旋电压/电流

• 批准号: EP/G051631/1
• 负责人: Atsufumi Hirohata
• 金额: $ 11.88万
• 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: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FG051631%2F1
• 关键词: Efficient; spin; voltage; current; generation

A spin-polarised electron current has been widely investigated to realise new spintronic device application. For example, spin-transfer torque induced by a spin-polarised electron current offers a fundamental physical mechanism on current-induced magnetisation switching (CIMS) as well as domain-wall motion in a ferromagnetic (FM) nanowire. The spin-transfer torque was predicted by Berger and Slonczewski independently, and has been experimentally demonstrated. By spin-scattering layer insertion and shape modification for a giant magnetoresistive (GMR) nanopillar, a critical current density for switching has been reduced to satisfy a Gbit-scale requirement for a magnetic random access memory (MRAM), a 4-Mbit version of which has been introduced by Freescale (now EverSpin Technologies) in 2006. MRAM is expected to replace a Si-based RAM due to the non-volatility and the better thermal stability. Recently, coherent tunnelling in an Fe/MgO/Fe system has been predicted to achieve over 1000% tunnelling magnetoresistance (TMR) and experimentally observed in epitaxial/highly-oriented Fe(Co)/MgO/Fe(Co) junctions. Such coherent tunnelling has been implemented into a nano-pillar to demonstrate the CIMS with 160% TMR ratio at room temperature. By combining the large TMR ratio with the substantial decrease in critical current density down to 2.5x10^6 A/cm2, the requirement for beyond the Gbit-scale MRAM application is satisfied. Hence, government-initiatives have been applied to develop a commercial Gbit MRAM both in the USA and Japan.Recent development in nanometre-scale fabrication techniques will enable us to expand a vertical GMR nanopillar into a lateral configuration, consisting of ferromagnetic nanowires and a non-magnetic nanowire to bridge over the spin injector and detector, enabling precise control of dimensions. In such a lateral spin-valve configuration, spin-polarised electrons can be injected with an electron charge current (local geometry) and without a charge current (non-local geometry). Using non-local geometry pioneering work has been performed by Jedema et al., successfully demonstrating diffusive spin injection from a ferromagnetic Ni80Fe20 nano-electrode, spin accumulation in a non-magnetic Cu nano-wire and spin detection by another NiFe nano-electrode. They have further extended their study into ballistic spin injection by inserting an AlOx tunnel barrier (insulator, I) at the FM/non-magnet (NM) interfaces. Consequently non-local spin-valve systems have been extensively employed to achieve efficient spin injection by minimising interfacial scattering in both diffusive and ballistic contacts and also to detect both spin Hall and inverse spin Hall effects. This clearly indicates the advantages of the lateral device configurations.In this proposed project, we will employ a lateral spin-valve structure instead of a conventional nano-pillar to demonstrate efficient generation of a spin voltage and current, which is not associated with an electron-charge current and hence minimises the Joule heating. In our proposed devices, both a spin current and a spin-polarised electron-charge current will be used to detect the spin voltage/current generation in non-local and local measurement geometries, respectively by changing the measurement geometries. In the non-local geometry , a spin current can be injected efficiently into a non-magnet through a tunnel barrier and detected as a large spin voltage through a second tunnel barrier. This gives a large spin current through a metallic interface. Our proposed device will therefore act independently as a pure spin-voltage and spin-current source with high efficiency. The evaluation of the pure spin-voltage and current will reveal the fundamental mechanism of spin-current transport (without an electron charge), which will encourage further theoretical studies for better understanding of the spin current and will also lead a new type of device architecture.

自旋极化电子流已被广泛研究以实现新的自旋电子器件应用。例如，自旋极化电子流引起的自旋转移力矩为电流感应磁化翻转（CIMS）以及铁磁（FM）纳米线中的磁畴壁运动提供了基本物理机制。自旋转移矩由 Berger 和 Slonczewski 独立预测，并已通过实验证明。通过巨磁阻 (GMR) 纳米柱的自旋散射层插入和形状修改，开关的临界电流密度已降低，以满足磁性随机存取存储器 (MRAM) 的 Gbit 级要求，飞思卡尔（Freescale，现为 EverSpin Technologies）已于 2006 年推出了 4 Mbit 版本。由于 MRAM 的非易失性和稳定性，预计将取代 Si 基 RAM。 热稳定性越好。最近，Fe/MgO/Fe 系统中的相干隧道预计将实现超过 1000% 的隧道磁阻 (TMR)，并在外延/高取向 Fe(Co)/MgO/Fe(Co) 结中进行了实验观察。这种相干隧道效应已被应用到纳米柱中，以证明 CIMS 在室温下具有 160% TMR 比。通过将大 TMR 比与临界电流密度大幅降低至 2.5x10^6 A/cm2 相结合，满足了超过 Gbit 规模的 MRAM 应用的要求。因此，美国和日本都已采取政府举措来开发商用 Gbit MRAM。纳米级制造技术的最新发展将使我们能够将垂直 GMR 纳米柱扩展为横向配置，由铁磁纳米线和非磁性纳米线组成，桥接自旋注入器和探测器，从而实现尺寸的精确控制。在这种横向自旋阀配置中，自旋极化电子可以在有电子充电电流（局部几何形状）的情况下注入，也可以在没有充电电流（非局部几何形状）的情况下注入。 Jedema 等人利用非局域几何进行了开创性工作，成功演示了铁磁性 Ni80Fe20 纳米电极的扩散自旋注入、非磁性 Cu 纳米线中的自旋累积以及另一个 NiFe 纳米电极的自旋检测。他们通过在 FM/非磁体 (NM) 界面插入 AlOx 隧道势垒（绝缘体，I），进一步将研究扩展到弹道自旋注入。因此，非局部自旋阀系统已被广泛采用，通过最大限度地减少扩散接触和弹道接触中的界面散射来实现有效的自旋注入，并检测自旋霍尔效应和逆自旋霍尔效应。这清楚地表明了横向器件配置的优势。在这个拟议的项目中，我们将采用横向自旋阀结构而不是传统的纳米柱来演示自旋电压和电流的有效生成，这与电子充电电流无关，因此最大限度地减少了焦耳热。在我们提出的设备中，自旋电流和自旋极化电子电荷电流将用于通过改变测量几何形状分别检测非局部和局部测量几何形状中的自旋电压/电流生成。在非局部几何结构中，自旋电流可以通过隧道势垒有效地注入非磁体，并通过第二隧道势垒检测为大自旋电压。这会通过金属界面产生大的自旋电流。因此，我们提出的器件将独立地充当高效率的纯自旋电压和自旋电流源。对纯自旋电压和电流的评估将揭示自旋电流传输（无电子电荷）的基本机制，这将鼓励进一步的理论研究以更好地理解自旋电流，并且还将引领一种新型的器件架构。

项目成果

Heusler-alloy films for spintronic devices

• DOI: 10.1007/s00339-013-7679-2
• 发表时间: 2013-05-01
• 期刊: APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING
• 影响因子: 2.7
• 作者: Hirohata, Atsufumi;Sagar, James;Lazarov, Vlado K.
• 通讯作者: Lazarov, Vlado K.

Schottky Barrier Height in Fe/GaAs Films

• DOI: 10.1109/tmag.2010.2045483
• 发表时间: 2010-05
• 期刊: IEEE Transactions on Magnetics
• 影响因子: 2.1
• 作者: L. Fleet;K. Yoshida;H. Kobayashi;Y. Ohno;H. Kurebayashi;J. Kim;C. Barnes;A. Hirohata

POLYCRYSTALLINE CO-BASED FULL-HEUSLER-ALLOY FILMS FOR SPINTRONIC DEVICES

用于自旋电子器件的多晶钴基全霍斯勒合金薄膜

• DOI: 10.1142/s2010324714400219
• 发表时间: 2015
• 期刊: SPIN
• 影响因子: 1.8
• 作者: HIROHATA A

Uniaxial anisotropy of two-magnon scattering in an ultrathin epitaxial Fe layer on GaAs

• DOI: 10.1063/1.4792269
• 发表时间: 2013-02
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: H. Kurebayashi;T. Skinner;K. Khazen;K. Olejník;D. Fang;C. Ciccarelli;R. Campion;B. Gallagher

Interfacial structure and transport properties of Fe/GaAs(001)

• DOI: 10.1063/1.3554267
• 发表时间: 2011-03
• 期刊: Journal of Applied Physics
• 影响因子: 3.2
• 作者: L. Fleet;H. Kobayashi;Y. Ohno;Jun-young Kim;C. Barnes;A. Hirohata