Spin-torque-induced switching and precession in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions
Spin-torque-induced switching and precession in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions
复制标题
DOI：
10.1103/physrevb.80.174405
复制
发表时间：
2009-11-01
影响因子：
3.7
通讯作者：
Fert, Albert
中科院分区：
文献类型：
--
作者：
Matsumoto, Rie;Fukushima, Akio;Fert, Albert
我们实验研究了全外延Fe(001)/MgO(001)/Fe(001)磁性隧道结(MTJ)中的电流驱动振荡，为更好地理解基于织构MTJ的自旋扭矩纳米振荡器(STNO)的微波振荡线宽(几百MHz)远大于基于电流垂直平面巨磁电阻结的STNO的微波振荡线宽(小于10 MHz)铺平了道路。外延Fe/MgO/Fe STNO是一个研究自旋转移扭矩物理的模型系统，因为它具有定义良好的单晶势垒和具有原子平坦界面的电极层。在Fe/MgO/Fe STNO中，外延MTJ中观察到明显的自旋扭矩诱导的开关和自旋扭矩的进动。当初始磁排列反平行且偏置电流超过阈值电流时，自旋扭矩补偿了阻尼，STNO显示出峰值强度迅速增加，峰值频率红移和最小线宽，所有这些都清楚地证明了自旋扭矩诱导的进动高于阈值电流。STNO的最小线宽为200 MHz，与织构CoFeB/MgO/CoFeb MTJ的线宽相当。这表明，大线宽的起源不能归因于织构MTJ的结构不均匀。当初始磁排列平行时，微波频谱呈现单峰，这在没有垂直磁场的织构MTJ中是很少观察到的。单峰振荡的机制可以通过考虑生长在MgO(001)势垒层上的3 nm厚的Fe(001)自由层的感应垂直磁各向异性来解释。
We experimentally investigated current-driven oscillation in fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) to pave the way for a better understanding of why the linewidth (a few hundred MHz) of microwave oscillation in spin-torque nano-oscillators (STNOs) based on textured MTJs is much larger than that (smaller than 10 MHz) in STNOs based on current-perpendicular-to-plane giant-magnetoresistance junctions. The epitaxial Fe/MgO/Fe STNO is a model system for studying the physics of spin-transfer torque because it has a well-defined single-crystal barrier and electrode layers with atomically flat interfaces. In the Fe/MgO/Fe STNOs, clear spin-torque-induced switching and spin-torque-induced precession were observed in epitaxial MTJs. When the initial magnetic alignment was antiparallel and the bias current exceeded the threshold current, a state in which the spin-torque compensates for the damping, the STNOs showed a rapid increase in the peak intensity, a redshift of the peak frequency, and a minimum linewidth, all clear evidence of spin-torque-induced precession above the threshold current. The minimum linewidth of the STNOs was 200 MHz, which is comparable to that of textured CoFeB/MgO/CoFeB MTJs. This indicates that the origin of the large linewidth cannot be attributed to structural inhomogeneity in textured MTJs. When the initial magnetic alignment was parallel, the microwave spectrum showed a single peak, which has rarely been observed in textured MTJs without application of a perpendicular magnetic field. The mechanism of the single-peak oscillation can be explained by taking account of the induced perpendicular magnetic anisotropy in the 3-nm-thick Fe(001) free layer grown on the MgO(001) barrier layer.