1111.3702 (Luqiao Liu et al.)

Review and Analysis of Measurements of the Spin Hall Effect in Platinum    [PDF]

Luqiao Liu, R. A. Buhrman, D. C. Ralph

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.

View original: http://arxiv.org/abs/1111.3702