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[转载]封面文章 | 锰氧化物纳米线的“可视化”隧穿磁阻效应
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第一作者 | 郁扬
通讯作者 | 郭杭闻，殷立峰，沈健
CPB2020年第1期封面文章导读
锰氧化物纳米线的“可视化”隧穿磁阻效应
研究亮点
本工作利用先进的微纳加工和磁性成像技术，在具有 “隧穿磁阻”效应的锰氧化物纳米线中，首次直接表征了隧穿磁阻发生过程中磁畴的演化过程。进一步结合磁电输运测量，提出了区别于传统隧穿磁阻效应的全新物理机制，为实现无化学界面的新奇隧穿磁阻结构提供了强有力依据。
研究背景
近二十年来，“隧穿磁阻（Tunnel Magnetoreisitance）”效应不仅是自旋电子学领域的研究热点，更是现代高密度磁存储和半导体工业的核心原理。在绝大多数情况下，隧穿磁阻的结构是由两种或三种不同材料组成的“三明治”结构。这种结构存在多个物理和化学界面，因此不仅生长和制备工艺较为复杂，而且自旋输运效率也会受到影响。有意思的是，锰氧化物中存在的“电子相分离”现象为隧穿磁阻带来了全新的可能。在亚微米尺度下，锰氧化物中内禀存在的铁磁金属畴和反铁磁绝缘畴可自发排序，形成有效的隧穿磁阻结构。这类隧穿磁阻不存在化学界面，因而大大简化了隧穿磁阻结构的复杂性。然而，其磁畴演化过程和形成磁电阻的物理机制却十分不明朗。因此，本工作旨在通过磁力显微镜等手段，在实空间中研究磁畴的演化规律和磁电阻的形成机制。
研究方法及结果
本工作中，作者使用微纳加工技术，首先在锰氧化物纳米线中测量到了高达290%的隧穿磁阻效应。更重要地，利用先进的变温-大磁场磁力显微镜成像技术，在纳米线中直接观察到了不同磁场下磁畴的空间演化过程。作者发现，隧穿磁阻的变化与磁畴演变所形成导电通道的打开和关闭密切相关。在高磁场时，绝大部分铁磁金属畴的磁化方向相同，因此自旋极化电子可以在纳米线中无阻碍的传输，此时体系处于低电阻态；而在低磁场时，由于反铁磁相互作用的存在，近邻的铁磁金属畴会出现磁化方向相反的现象。当磁化方向相反的两个磁畴覆盖了纳米线的宽度时，自旋极化电子在磁畴的界面处遇到阻碍，必须隧穿通过畴界进行传输，因此处于高电阻态，从而实现隧穿磁阻效应。因此，通过直接观察磁畴的演化过程以及磁电输运的测量，作者很好地发现了这类内禀隧穿磁阻体系的物理机制。
研究意义或前景
本工作对磁畴的演化过程进行了直接的表征，发现了一种全新的隧穿磁阻效应机理，与传统的隧穿磁阻效应大相径庭。这一发现为隧穿磁阻效应的发展提供了全新的策略，并为这一方向的发展提出了新的途径和展望。
文章来源
Chin. Phys. B, 2020, 29 (1): 018501
原文概览
Visualization of tunnel magnetoresistance effect in single manganite nanowires
Yang Yu(郁扬)1, Wenjie Hu(胡雯婕)1, Qiang Li(李强)1, Qian Shi(时倩)1, Yinyan Zhu(朱银燕)1, Hanxuan Lin(林汉轩)1, Tian Miao(苗田)1, Yu Bai(白羽)1, Yanmei Wang(王艳梅)1, Wenting Yang(杨文婷)1, Wenbin Wang(王文彬)2, Hangwen Guo(郭杭闻)2, Lifeng Yin(殷立峰)1,2,3, Jian Shen(沈健)1,2,3
1 State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China;
2 Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China;
3 Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
We reported a study of tunnel magnetoresistance (TMR) effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging. TMR value up to 290% has been observed in single (La1-yPry)1-xCaxMnO3 nanowires with varying width. We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions. Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.
Keywords: manganite nanowires, tunnel magnetoresistance, magnetic force microscope
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https://blog.sciencenet.cn/blog-3377544-1233170.html
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