Domain-wall velocities of up to 750 m s-1 driven by exchange-coupling torque in synthetic antiferromagnets
Domain-wall velocities of up to 750 m s-1 driven by exchange-coupling torque in synthetic antiferromagnets
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DOI：
10.1038/nnano.2014.324
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发表时间：
2015-03-15
影响因子：
38.3
通讯作者：
Parkin, Stuart
中科院分区：
文献类型：
--
作者：
Yang, See-Hun;Ryu, Kwang-Su;Parkin, Stuart
跑道存储器（1-3）的操作基于原子级薄的垂直磁化纳米线中的畴壁的运动，所述纳米线与具有高自旋轨道耦合的相邻金属层接合。这种畴壁具有手性Neel结构（4-7），并且可以通过电流（5，6）有效地移动。高容量赛道存储器需要紧密堆积的畴壁，但它们的密度受到来自边缘磁场的偶极耦合的限制（3）。这些场可以使用由两个磁性子层组成的合成反铁磁结构来消除，所述两个磁性子层经由反铁磁耦合间隔层（8）交换耦合。在这里，我们表明，纳秒长的电流脉冲可以移动畴壁合成反铁磁赛道，几乎为零净磁化。与子层铁磁耦合的类似跑道相比，畴壁可以更有效地移动，并且速度更高（高达750 m s（-1））。这是由于Neel畴壁结构的稳定性，以及与两个子层之间的反铁磁交换耦合的强度成正比的交换耦合扭矩。此外，由于交换耦合力矩的作用，壁面速度对沿纳米线沿着施加的磁场的依赖性不同于单层跑道。没有净磁化的跑道中的高畴壁速度允许密集堆积但高效的基于畴壁的自旋电子学。
The operation of racetrack memories(1-3) is based on the motion of domain walls in atomically thin, perpendicularly magnetized nanowires, which are interfaced with adjacent metal layers with high spin-orbit coupling. Such domain walls have a chiral Neel structure(4-7) and can be moved efficiently by electrical currents(5,6). High-capacity racetrack memory requires closely packed domain walls, but their density is limited by dipolar coupling from their fringing magnetic fields(3). These fields can be eliminated using a synthetic antiferromagnetic structure composed of two magnetic sub-layers, exchange-coupled via an ultrathin antiferromagnetic-coupling spacer layer(8). Here, we show that nanosecond-long current pulses can move domain walls in synthetic antiferromagnetic racetracks that have almost zero net magnetization. The domain walls can be moved even more efficiently and at much higher speeds (up to similar to 750 m s(-1)) compared with similar racetracks in which the sub-layers are coupled ferromagnetically. This is due to a stabilization of the Neel domain wall structure, and an exchange coupling torque that is directly proportional to the strength of the antiferromagnetic exchange coupling between the two sub-layers. Moreover, the dependence of the wall velocity on the magnetic field applied along the nanowire is distinct from that of the single-layer racetrack due to the exchange coupling torque. The high domain wall velocities in racetracks that have no net magnetization allow for densely packed yet highly efficient domain-wall-based spintronics.