International Iberian Nanotechnology Laboratory, INL, Av. Mestre José Veiga s/n, 4715-330, Braga, Portugal.
IN-IFIMUP, Rua do Campo Alegre, 687, 4169-007, Porto, Portugal.
Sci Rep. 2017 Aug 3;7(1):7237. doi: 10.1038/s41598-017-07762-z.
Reported steady-state microwave emission in magnetic tunnel junction (MTJ)-based spin transfer torque nano-oscillators (STNOs) relies mostly on very thin insulating barriers [resulting in a resistance × area product (R × A) of ~1 Ωμm] that can sustain large current densities and thus trigger large orbit magnetic dynamics. Apart from the low R × A requirement, the role of the tunnel barrier in the dynamics has so far been largely overlooked, in comparison to the magnetic configuration of STNOs. In this report, STNOs with an in-plane magnetized homogeneous free layer configuration are used to probe the role of the tunnel barrier in the dynamics. In this type of STNOs, the RF modes are in the GHz region with integrated matched output powers (P ) in the range of 1-40 nW. Here, P values up to 200 nW are reported using thicker insulating barriers for junctions with R × A values ranging from 7.5 to 12.5 Ωμm, without compromising the ability to trigger self-sustained oscillations and without any noticeable degradation of the signal linewidth (Γ). Furthermore, a decrease of two orders of magnitude in the critical current density for spin transfer torque induced dynamics (J ) was observed, without any further change in the magnetic configuration.
基于磁隧道结（MTJ）的自旋转移扭矩纳米振荡器（STNO）中报道的稳定微波发射主要依赖于非常薄的绝缘势垒[导致电阻×面积乘积（R×A）约为 1 Ωμm]，这种势垒可以承受大电流密度，从而引发大的轨道磁动力学。除了低 R×A 的要求外，与 STNO 的磁结构相比，隧道势垒在动力学中的作用迄今为止在很大程度上被忽视了。在本报告中，使用具有面内磁化的均匀自由层结构的 STNO 来探测隧道势垒在动力学中的作用。在这种类型的 STNO 中，RF 模式处于 GHz 区域，集成的匹配输出功率（P）在 1-40nW 的范围内。这里，使用较厚的绝缘势垒报告了高达 200nW 的 P 值，而对于 R×A 值在 7.5 到 12.5 Ωμm 之间的结，不会影响触发自维持振荡的能力，也不会对信号线宽（Γ）产生任何明显的劣化。此外，还观察到用于自旋转移扭矩诱导动力学（J）的临界电流密度降低了两个数量级，而磁结构没有任何进一步的变化。
