Synthetic Antiferromagnetic Skyrmions

在这个项目中，我们将稳定手性合成反铁磁多层膜中称为skyrmions的小圆形磁畴，并研究它们的电流驱动动力学。该项目基于我们团队最近的两项突破：我们能够在适当设计的单手性垂直磁化层中稳定skyrmions作为拓扑保护结构（使它们抵抗湮灭），并且能够在简单的平面内磁化合成反铁磁体中以低电流密度移动耦合拓扑缺陷（畴壁）。虽然传统的skyrmions是各种新型信息存储和处理设备的有趣候选器件，提供了极低功耗操作的前景，但由于拓扑阻尼，它们预计在小尺寸下移动缓慢，并且由于Magnus力导致skyrmions霍尔效应而使其与当前驱动方向成一定角度。为了实现它们的潜力，我们需要建立最佳的多层结构来支持合成的反铁磁skyrmions，这些skyrmions体积小，机动性高，并且在电流驱动的方向上移动。我们需要找到一种可靠的成核方法，以可控的方式合成反铁磁粒子，以便进一步研究。我们需要知道如何通过平衡两分量skyrmions上的Magnus力使skyrmions霍尔角减小到零，从而使合成反铁磁skyrmions直接响应自旋电流驱动。最后，我们需要学习如何利用预期的拓扑阻尼抑制，以使合成的反铁磁skyrmions以比传统skyrmions更高的速度和更小的尺寸移动。在这个项目中，我们将制备支持合成反铁磁skyrmions的手性磁性多层膜，对skyrmions结构进行成像，并制造纳米级器件，在该器件中我们可以测量电流驱动的skyrmions动力学。我们将结合我们在合成反铁磁多层材料方面的专业知识，以及我们在界面处诱导强Dzyaloshinskii-Moriya相互作用的成熟能力，将两个极性和手性相反的耦合skyrmion结合成一个可以在室温下稳定的合成反铁磁skyrmion，并使用最先进的显微镜技术对其结构和运动进行场成像。接下来，我们将研究人工合成的反铁磁粒子在随机发生和故意引入的缺陷下的成核，这些缺陷是由磁场脉冲或电流刺激引起的。然后，我们将准备skyrmion赛道，合成的反铁磁skyrmion可以使用从优化的多层堆栈中产生的电流驱动扭矩推进，并在中等电流密度下对skyrmion运动进行成像，以测量skyrmion霍尔角并找到它为零的条件。我们将继续增加电流密度，利用抑制合成反铁磁体中耦合拓扑缺陷之间产生的拓扑阻尼来寻求高速斯基米子运动。我们将获得的结果不仅会通过揭示这种新型材料组合所提供的可能性而导致高影响力的出版物和会议报告，而且还会在基于合成反铁磁粒子的自旋电子学领域开发潜在的有价值的技术应用。

In this project we will stabilise small circular magnetic domains called skyrmions in chiral synthetic antiferromagnetic multilayers and study their current-driven dynamics. The project is based on two recent breakthroughs by our groups: our being able to stabilise skyrmions as a topologically protected structure (making them resistant to annihilation) in a suitably designed single chiral perpendicularly magnetised layer, and being able to move coupled topological defects (domain walls) at low current density in a simple in-plane magnetised synthetic antiferromagnet.Whilst conventional skyrmions are interesting candidates for a variety of novel information storage and processing devices that offer the prospect of very low power operation, they are expected to move slowly at small sizes due to topological damping and are diverted at an angle to their current drive direction by the Magnus forces that lead to a skyrmion Hall effect. To realise their potential, we need to establish the optimal multilayer structure to support synthetic antiferromagnetic skyrmions that are small, highly mobile, and move in the direction of an electrical current drive. We need to find a reliable nucleation method to that can create synthetic antiferromagnetic skyrmions in a controlled manner for further study. We need to know how make synthetic antiferromagnetic skyrmions respond directly to spin current drives by balancing the Magnus forces on the two component skyrmions to reduce the skyrmion Hall angle to zero. Finally, we need to learn how to exploit the expected suppression of topological damping in order to move the synthetic antiferromagnetic skyrmions move at velocities far higher, and at smaller sizes, than for conventional skyrmions. In this project we will prepare chiral magnetic multilayers that support synthetic antiferromagnetic skyrmions, image the skyrmion structures, and fabricate nanoscale devices in which we can measure current-driven skyrmion dynamics. We will combine our expertise with synthetic antiferromagnet multilayers with our proven ability to induce strong Dzyaloshinskii-Moriya interactions at interfaces to combine two coupled skyrmions with opposite polarity and chirality into a synthetic antiferromagnetic skyrmion that can be stabilised at room temperature, with their structure and motion under field imaged using state-of-the-art microscopy techniques. Next, we will study the nucleation of synthetic antiferromagnetic skyrmions at randomly occurring and deliberately introduced defects due to the application of stimuli including pulses of magnetic field or electrical current. We will then prepare skyrmion racetracks along which synthetic antiferromagnetic skyrmions can be propelled using current-driven torques from this optimised multilayer stack and image the skyrmion motion at moderate current densities in order to measure the skyrmion Hall angle and find the conditions when it is zero. We will go on to increase the current densities to seek high velocity skyrmion motion exploiting the suppression of topological damping that arises between coupled topological defects in synthetic antiferromagnets.The results we shall obtain will not only lead to high impact publications and conference presentations by shedding light on the possibilities offered by this novel combination of materials, but also develop potentially valuable knowhow in the field of spintronics based on synthetic antiferromagnetic skyrmions for technological applications.