Review and Analysis of Measurements of the Spin Hall Effect in Platinum
Review and Analysis of Measurements of the Spin Hall Effect in Platinum
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发表时间：
2011-11
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通讯作者：
Luqiao Liu;R. Buhrman;D. Ralph
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作者：
Luqiao Liu;R. Buhrman;D. Ralph
几种不同的实验技术被用于测量Pt样品在室温下的自旋霍尔电导率和自旋霍尔角，结果相差超过20倍，自旋霍尔电导率从2.4 × 10^4到5.1 × 10^5 [hbar/(2e)]（欧姆-m）^-1，自旋霍尔角从0.0037到0.08。我们回顾了这项工作，并分析了差异的可能原因。我们解释说，根据侧向坡莫合金/铜/铂器件的测量结果所报道的自旋霍尔角的最小值是不正确的，因为最初的分析没有适当考虑到这些器件中的铜层将分流流过相邻铂线的电荷电流，从而大大减小了自旋霍尔相关信号的大小。我们认为，其他实验技术发现的自旋霍尔角结果之间的差异主要是由于对Pt中自旋扩散长度的不同假设的结果。我们提出了在室温下溅射Pt/坡莫合金双层薄膜中Pt中自旋扩散长度的新测量，发现1.4 \pm 0.3 nm，比以前通常假设的值小得多。利用这个自旋扩散长度值，可以使先前不一致的结果得到更好的一致性，自旋霍尔电导率为（1.4 - 3.4）× 10^5 [hbar/(2e)]（欧姆-m）^-1，自旋霍尔角大于0.05。这些值足够大，以至于Pt中的自旋霍尔效应可以用来产生足够强的自旋电流和自旋转移力矩，从而有效地操纵相邻铁磁层中的磁矩。
Several different experimental techniques have been used in efforts to measure the spin Hall conductivity and the spin Hall angle in Pt samples at room temperature, with results that disagree by more than a factor of 20, with spin Hall conductivities from 2.4 x 10^4 to 5.1 x 10^5 [hbar/(2e)] (Ohm-m)^-1 and spin Hall angles from 0.0037 to 0.08. We review this work, and analyze possible reasons for the discrepancies. We explain that the smallest values for the spin Hall angle that have been reported, based on measurements of lateral permalloy/copper/platinum devices, are incorrect because the original analyses did not properly take into account that copper layers in these devices will shunt charge current flowing through adjacent platinum wires, thereby greatly reducing the size of the spin-Hall-related signals. We suggest that differences between the results for the spin Hall angle found by other experimental techniques are primarily a consequence of different assumptions about the value of the spin diffusion length in Pt. We present a new measurement of the spin diffusion length in Pt within sputtered Pt/permalloy bilayer thin films at room temperature, finding 1.4 \pm 0.3 nm, a much smaller value than has generally been assumed previously. With this value for the spin diffusion length, the previously-discordant results can be brought into much better agreement, with the result that the spin Hall conductivities are (1.4 - 3.4) x 10^5 [hbar/(2e)] (Ohm-m)^-1 and the spin Hall angles are greater than 0.05. These values are sufficiently large that the spin Hall effect in Pt can be used to generate spin currents and spin transfer torques strong enough for efficient manipulation of magnetic moments in adjacent ferromagnetic layers.