石墨烯锯齿型晶界局域态的磁性和自旋传输特性研究

Graphene has long spin life times and long diffusion lengths at room temperature, making it highly promising for spintronics. However, pristine graphene is diamagnetic and making graphene magnetic remains a principal challenge. It was shown by theoretical studies that graphene zig-zag grain boundaries with localized states can form long magnetic ordering and work as spin-filtering. However, there is no experimental report so far. Applicant has prepared graphene with zig-zag grain boundaries in a controllable way, experimentally confirmed the presence of the localized states, and also theoretically demonstrated the spin-filtering effect. In this project, we will continue to investigate the magnetic and spin-dependent transport properties of graphene with zig-zag boundaries. We will form and improve long magnetic ordering using elements doping and magnetic coupling of grain boundaries. We will also plan to confirm the spin-filtering effect of single grain boundary by measuring the spin current crossing grain boundary based on inverse spin hall effect and demonstrate how spin-filter effect is affected by spin-orbit coupling and bias voltage. We will also intent to measure the magneto-resistance of electrons crossing two antiferromagnetic coupled grain boundaries and investigate how to rotate magnetic moments of graphene boundary with magnetic field and spin-polarized current. We also plan to study the spin relaxation induced by grain boundary through measuring the nonlocal magneto-resistance based on devices with ferromagnet/tunnel barrier. Through the implementation of this project, we will make ferromagnetic graphene, design the spin-filter based on single grain boundary, and fabricate atomic thick spin valve based on two magnetic coupled grain boundaries.

石墨烯有很长的自旋寿命和自旋扩散长度，是理想的自旋电子学材料，但是石墨烯是抗磁体，如何有效地引入自旋是该领域的重要问题。理论研究表明锯齿型晶界局域态可以实现磁长程有序并产生自旋过滤效应，但尚未有相关实验报道。申请人已可控制备出具有锯齿型晶界的石墨烯，证实了晶界局域态的存在，从理论上展示了自旋过滤效应。鉴于此，本项目将以锯齿型晶界石墨烯为研究对象，通过掺杂、晶界磁耦合等手段来调控磁有序；通过测量逆自旋霍尔效应研究电子垂直隧穿晶界的自旋流密度，阐述自旋轨道耦合和横向偏压对自旋过滤效应的调制；通过测量电子垂直隧穿两个具有反铁磁耦合晶界的磁电阻，研究磁场和自旋极化电流对晶界磁矩的反转；通过测量基于磁铁/势垒层的非局域磁电阻，研究晶界对自旋的驰豫。本项目的实施，预期将实现铁磁石墨烯；构筑基于单个晶界的自旋过滤器和基于两个晶界磁耦合的原子层厚度自旋阀；为设计和构筑全碳自旋器件奠定实验基础。

本项目的研究课题来源于二维材料自旋电子学的核心问题-如何在石墨烯和类石墨烯材料中引入自旋自由度，采取的手段主要包括，锯齿形边缘态，磁近邻效应，局域态（气体吸附和元素掺杂）调控引入局域磁矩，及弯曲应变调控自旋轨道耦合效应等。四年来，课题组成员详细研究了二维材料磁性的现状及存在的问题，回顾了非磁性重金属/磁绝缘体异质结的磁输运性质。在锯齿形边缘态，气体吸附调控局域态，磁近邻效应和弯曲应变调控石墨烯和类石墨烯材料磁阻及输运特性领域取得了一系列研究成果，在国际高水平期刊上发表SCI论文15篇，培养博士研究生3名，硕士就研究生4名。遗憾的是，虽然制备的石墨烯晶界具有锯齿形局域态，但是晶界和晶界之间出现了畴，畴壁散射了绝大部分锯齿型晶界局域态产生的自旋极化电流，导致晶界耦合效应不明显，可发表的数据不多。庆幸的是利用发展出的气体吸附调控局域态方法，我们设计了多种气体传感器和多值存储器；基于发展出的弯曲应变调控二维材料传输特性方法，我们设计了具有高响应度的应变传感器。此外，我们还构建了石墨烯/磁性二维材料异质结，其中磁性二维材料具有锯齿形边缘结构，且该异质结石墨烯的曲率半径可以通过弯曲应变来调控。这些方法对国内外同行的研究提供了新的思路，同时，也为我们将来的研究工作打下了坚实的基础。