Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator
Time resolved imaging of the non-linear bullet mode within an injection-locked nano-contact spin Hall nano-oscillator
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DOI：
10.1063/1.5047148
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发表时间：
2018-05
影响因子：
4
通讯作者：
T. M. Spicer;P. Keatley;M. Dvornik;T. Loughran;A. Awad;P. Dürrenfeld;A. Houshang;M. Ranjbar;J. Åkerman;V. Kruglyak;R. Hicken
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作者：
T. M. Spicer;P. Keatley;M. Dvornik;T. Loughran;A. Awad;P. Dürrenfeld;A. Houshang;M. Ranjbar;J. Åkerman;V. Kruglyak;R. Hicken
时间分辨扫描克尔显微镜（TRSKM）已被用来成像进动磁化动力学的纳米接触（NC）自旋霍尔纳米振荡器（SHNO）内的直流电流激发。射频（RF）电流的注入用于将SHNO锁相至TRSKM。利用极性磁光克尔效应（MOKE）检测出面外磁化强度。然而，纵向MOKE图像主要是由伪影所产生的边缘的Au NC。时间分辨成像显示，一旦DC电流超过阈值，在装置的中心处的非线性“子弹”模式的同时激发，以及由RF电流诱导的铁磁共振（FMR）。然而，亚临界直流电流值观察到的FMR响应在中心处表现出幅度最小值，这归因于由于器件结构的电抗而导致的RF自旋电流的扩散。可以减去该FMR响应以产生子弹模式的图像。当DC电流增加到阈值以上时，子弹模式的大小似乎增加，表明平移运动增加。子弹型和FMR模式的空间重叠减少，以及这种假定的平移运动，可能会阻碍注射锁定，并导致在NC-SHNO器械内观察到的锁定范围减少。这说明了一个更普遍的需要控制注入锁定振荡器的几何形状，使振荡器的自主动态表现出强烈的空间重叠与那些从injected signal. Time分辨扫描克尔显微镜（TRSKM）已被用来成像进动磁化动力学纳米接触（NC）自旋霍尔纳米振荡器（SHNO）内的直流电流激发。射频（RF）电流的注入用于将SHNO锁相至TRSKM。利用极性磁光克尔效应（MOKE）检测出面外磁化强度。然而，纵向MOKE图像主要是由伪影所产生的边缘的Au NC。时间分辨成像显示，一旦DC电流超过阈值，在装置的中心处的非线性“子弹”模式的同时激发，以及由RF电流诱导的铁磁共振（FMR）。然而，亚临界直流电流值观察到的FMR响应在中心处表现出幅度最小值，这归因于由于器件结构的电抗而导致的RF自旋电流的扩散。可以减去该FMR响应以产生子弹模式的图像。由于直流电流在…
Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nano-oscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear “bullet” mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is increased above threshold, the bullet mode appears to increase in size, suggesting increased translational motion. The reduced spatial overlap of the bullet and FMR modes, and this putative translational motion, may impede the injection locking and contribute to the reduced locking range observed within NC-SHNO devices. This illustrates a more general need to control the geometry of an injection-locked oscillator so that the autonomous dynamics of the oscillator exhibit strong spatial overlap with those resulting from the injected signal.Time-resolved scanning Kerr microscopy (TRSKM) has been used to image precessional magnetization dynamics excited by a DC current within a nano-contact (NC) spin Hall nano-oscillator (SHNO). Injection of a radio frequency (RF) current was used to phase lock the SHNO to TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear “bullet” mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits an amplitude minimum at the centre, which is attributed to spreading of the RF spin current due to the reactance of the device structure. This FMR response can be subtracted to yield images of the bullet mode. As the DC current is in...