Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan.
Nat Nanotechnol. 2012 Oct;7(10):635-9. doi: 10.1038/nnano.2012.151. Epub 2012 Sep 9.
Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold J(th)(0). Here, we show that domain wall motion can be induced at current densities 40% below J(th)(0) when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000 Oe, even at currents below J(th)(0). We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant.
通过电流控制磁畴壁的位置可能会允许新类型的非易失性存储和逻辑器件。然而，为了实际应用，畴壁运动所需的电流密度阈值必须降低到目前的值以下。最近在垂直磁化的 Co/Ni 纳米线中观察到的由于磁各向异性引起的固有钉扎，导致了固有电流阈值 J(th)(0)。在这里，我们表明，当施加畴壁钉扎场量级的外部磁场时，畴壁运动可以在低于 J(th)(0)的电流密度下被诱导。我们观察到畴壁运动的速度是电流和磁场诱导速度的矢量和，并且畴壁可以在低于 J(th)(0)的电流下，沿着高达 2000 Oe 的磁场方向被驱动。我们表明，这种违反直觉的现象是由 Walker 击穿触发的，并且附加速度提供了一种同时确定电流的自旋极化和 Gilbert 阻尼常数的独特方法。
