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. Author manuscript; available in PMC: 2017 Sep 6.
Published in final edited form as: Rev Mod Phys. 2017 Jun 5;89(2):025006. doi: 10.1103/RevModPhys.89.025006

Figure 12.

Figure 12

(a) In a bilayer of a heavy metal and ferromagnet (e.g., Pt/permalloy (Py)) in which spin torque is created by the spin Hall effect, the charge current density J and the spin current density JS pass through very different areas a and A respectively. (b) High torque efficiency is possible because each electron transfers spin to Py several times, as described in the text.