Monopole defects and magnetic Coulomb blockade
Monopole defects and magnetic Coulomb blockade
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DOI：
10.1088/1367-2630/13/2/023023
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发表时间：
2011-02-10
影响因子：
3.3
通讯作者：
Cohen, Lesley F.
中科院分区：
文献类型：
--
作者：
Ladak, Sam;Read, Dan;Cohen, Lesley F.
狄拉克预言的磁单极子进入了一个新的范式，发现了偶极晶格内出现的单极子，即块状和人造自旋冰。在某些人工系统中观察单极子，以及在其他类似结构中不存在单极子，是一个重大难题。连接的人造自旋冰结构在电读取状态的可能性方面引起了广泛关注，并提供了通过充分理解的畴壁过程控制单极子缺陷的可能性。然而，缺乏对基本过程的充分理解。在这里，我们建立了最重要的组件之一。我们使用高分辨率扫描透射 X 射线显微镜 (STXM) 演示了与两个横向畴壁相关的协同过程，该过程在 NiFe 中产生单极子缺陷。与铁磁体中的交换长度相比，阵列的特征尺寸很大，并且两个横向畴壁为单极子缺陷顶点提供了丰富的内部结构。带有相同磁荷符号的两个畴壁之间的磁库仑斥力使单极子缺陷稳定在大于该顶点处单壁的脱钉场的场上。这些观察结果使我们能够对单极子缺陷控制的可能性进行概述，从 Co 阵列中的外在钉扎（极端外在极限是孤立的棒结构）到此处捕获的内在钉扎。
Magnetic monopoles, predicted by Dirac, entered a new paradigm with the discovery of emergent monopoles within dipole lattices known as bulk and artificial spin ices. The observation of monopoles in certain artificial systems, and their absence from other similar structures, is a significant puzzle. Connected artificial spin-ice structures attract much attention in terms of the possibility to read states electrically, and offer the possibility of monopole defect control via well-understood domain wall processes. Nevertheless, full comprehension of the underlying processes is lacking. Here, we establish one of the overriding components. We demonstrate using high-resolution scanning transmission x-ray microscopy (STXM) the cooperative process associated with two transverse domain walls that creates the monopole defect in NiFe. The feature size of the array is large compared to the exchange length in the ferromagnet, and the two transverse domain walls give a rich internal structure to the monopole defect vertex. The magnetic Coulomb repulsion between two domain walls carrying the same sign of magnetic charge stabilizes the monopole defects at fields greater than the depinning field for a single wall at that vertex. These observations allow us to form an overview of monopole defect control possibilities from extrinsic pinning as in Co arrays (the extreme extrinsic limit being isolated bar structures) to intrinsic pinning captured here.