Heteronuclear Metalloporphyrin Dimers for Molecular Spintronics

自旋阀是一种电子设备，它可以在两种状态之间切换--一种是低阻状态，另一种是高阻状态--以响应外部磁场。自20世纪80年代末首次开发以来，自旋阀通过在硬盘驱动器(HDD)、磁性传感器和磁性随机存取存储器(MRAM)中的存储单元中的应用极大地提高了磁数据存储容量，在塑造信息技术格局中发挥了重要作用。自旋阀的开发是自旋电子学研究领域的一部分，自旋电子学包括利用电子的电荷和自旋的设备。自旋是一种量子力学性质，有两个离散值：自旋上升或自旋下降。传统的自旋阀是两个导电磁层被一个非磁层隔开的三层器件。如果两个磁层的磁矩指向相同的方向，则器件的电阻较低，从而导致高电流。如果两个磁矩指向相反的方向，则电阻增加，从而产生较小的电流。这种行为是由电流的电子在穿过磁性层时的自旋极化引起的：所有的电子自旋都是向上或向下的，这取决于磁层的磁取向。只有当两个磁层有利于相同的自旋极化时，电子才能有效地通过器件，导致低阻状态并产生净自旋极化电流，通过施加外部磁场可以改变两个磁矩的相对取向。这允许在具有高电导的导通状态和低电导的关断状态之间进行磁响应切换。将磁环境的变化转化为电子信息是自旋阀广泛应用背后的关键概念。本项目的目标是合理设计、合成和研究单分子自旋阀的电子性质。单个分子是最小的稳定结构积木，只有几个纳米大小。因此，模仿宏观电子元件特性的功能分子的设计是电子电路最终微型化到纳米级的基础。到目前为止，这样的分子电路是难以捉摸的，但是不断增加的计算能力的需求和当前制造技术的固有限制使得向分子电子领域的过渡变得非常可取。我们的单分子自旋阀的合成方法是基于单个分子中的两个分子磁体和一根导线的组合。分子磁体将在流经导线的电流中产生自旋极化--类似于传统的自旋阀--两个磁中心需要有利于相同的自旋取向，才能产生通过该设备的强电流。单分子自旋阀的实现是在分子电子器件设计中理解基本结构性质关系的重要一步。它还在分子电路中作为磁响应开关以及在分子量子信息存储和量子计算中产生自旋极化电流等方面具有潜在的应用。这个多学科项目涉及广泛的技术，包括化学合成、理论建模、光谱测量、磁测量和低温电荷输运测量。该项目属于EPSRC量子技术研究领域，由牛津大学化学系和材料系密切合作进行。

A spin valve is an electronic device that can switch between two states - one of low resistance and one of high resistance - in response to an external magnetic field. Spin valves have played an important role in shaping the information technology landscape since their first development in the late 1980s by dramatically increasing magnetic data storage capacities with applications as read heads in hard disc drives (HDD), magnetic sensors, and memory unit in magnetic random-access memories (MRAM). The development of spin valves is part of the research field of spintronics - short for spin electronics - which comprises devices that make use of the charge and spin of electrons. Spin is a quantum-mechanical property that takes two discrete values: spin-up or spin-down.Traditional spin valves are three-layer devices in which two conductive magnetic layers are separated by a non-magnetic layer. If the magnetic moments of the two magnetic layers point in the same direction, the resistance of the device is low, which results in a high electric current. If the two magnetic moments point in opposite directions, the resistance increases leading to a smaller electric current. This behaviour is caused by the spin polarization of the electrons of the electric current when passing through the magnetic layers: all electron spins are oriented either "up" or "down" depending on the magnetic orientation of the layer. Only if the two magnetic layers favour the same spin polarization, electrons can travel though the device efficiently leading to the low resistance state and the generation of a net spin polarized current.The relative orientation of the two magnetic moments can be changed by applying an external magnetic field. This allows for the magnetoresponsive switching between an on-state with high conductance and a low conductance off-state. The translation of changes in the magnetic environment into electronic information is the key concept behind the broad range of application of spin valves.This project targets the rational design, synthesis and study of the electronic properties of a single-molecule spin valve. Individual molecules are the smallest stable structural building blocks with only a few nanometres in size. Therefore, the design of functional molecules that mimic the properties of macroscopic electronic components is fundamental for the ultimate miniaturization of electronic circuits to the nanometre scale. To date, such molecular circuits have been elusive, but the continuous demand for increasing computing powers and the inherent limits of present manufacturing techniques make the transition to a molecular electronics landscape highly desirable.Our approach for the synthesis of a single-molecule spin valve is based on the combination of two molecular magnets and a conductive wire in a single molecule. The molecular magnets will generate a spin polarization in the current passing through the wire and - analogous to a traditional spin valve - both magnetic centres need to favour the same spin orientation to result in a strong current through the device. The realization of a single-molecule spin valve is an important step towards understanding fundamental structure property relationships in the design of molecular electronic devices. It also has potential applications as a magnetoresponsive switch in a molecular circuit and for the generation of spin polarized currents for the use in molecular quantum information storage and quantum computing.This multidisciplinary project involves a wide range of techniques including chemical synthesis, theoretical modelling, spectroscopic measurements, magnetometry, and cryogenic charge transport measurements. The project falls within the EPSRC quantum technologies research area and is conducted in close collaboration between the Department of Chemistry and the Department of Materials at the University of Oxford.