Emori Satoru, Klewe Christoph, Schmalhorst Jan-Michael, Krieft Jan, Shafer Padraic, Lim Youngmin, Smith David A, Sapkota Arjun, Srivastava Abhishek, Mewes Claudia, Jiang Zijian, Khodadadi Behrouz, Elmkharram Hesham, Heremans Jean J, Arenholz Elke, Reiss Günter, Mewes Tim
Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, United States.
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Nano Lett. 2020 Nov 11;20(11):7828-7834. doi: 10.1021/acs.nanolett.0c01868. Epub 2020 Oct 21.
Spin currents can exert spin-transfer torques on magnetic systems even in the limit of vanishingly small net magnetization, as recently shown for antiferromagnets. Here, we experimentally show that a spin-transfer torque is operative in a macroscopic ensemble of weakly interacting, randomly magnetized Co nanomagnets. We employ element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to directly detect subnanosecond dynamics of the Co nanomagnets, excited into precession with cone angle ≳0.003° by an oscillating spin current. XFMR measurements reveal that as the net moment of the ensemble decreases, the strength of the spin-transfer torque increases relative to those of magnetic field torques. Our findings point to spin-transfer torque as an effective way to manipulate the state of nanomagnet ensembles at subnanosecond time scales.
自旋电流即使在净磁化强度极小的极限情况下也能对磁系统施加自旋转移力矩，最近在反铁磁体中已有相关证明。在此，我们通过实验表明，自旋转移力矩在弱相互作用、随机磁化的钴纳米磁体的宏观集合中起作用。我们采用元素分辨和时间分辨的X射线铁磁共振（XFMR）光谱法，直接检测钴纳米磁体的亚纳秒级动力学，通过振荡自旋电流将其激发到锥角≳0.003°的进动状态。XFMR测量结果表明，随着集合体净磁矩的减小，自旋转移力矩的强度相对于磁场力矩的强度增加。我们的研究结果表明，自旋转移力矩是在亚纳秒时间尺度上操纵纳米磁体集合体状态的有效方法。
