  Spin-orbit torque in heavy metal/ferromagnet heterostructures with broken
spatial inversion symmetry provides an efficient mechanism for manipulating
magnetization using a charge current. Here, we report the presence of a spin
torque in a single ferromagnetic layer in both asymmetric MgO/Fe0.8Mn0.2 and
symmetric MgO/Fe0.8Mn0.2/MgO structures, which manifests itself in the form of
an effective field transverse to the charge current. The current to effective
field conversion efficiency, which is characterized using both the nonlinear
magnetoresistance and second-order planar Hall effect methods, is comparable to
the efficiency in typical heavy metal/ferromagnet bilayers. We argue that the
torque is caused by spin rotation in the vicinity of the surface via impurity
scattering in the presence of a strong spin-orbit coupling. Instead of
cancelling off with each other, the torques from the top and bottom surfaces
simply add up, leading to a fairly large net torque, which is readily observed
experimentally.
