  An antiferromagnet is a promising material for spin-orbit torque generation.
Earlier studies of the spin-orbit torque in an antiferromagnet are limited to
collinear spin configurations. We calculate the spin-orbit torque in an
antiferromagnet whose spin ordering is weakly noncollinear. Such
noncollinearity may be induced spontaneously during the magnetization dynamics
even when the equilibrium spin configuration is perfectly collinear. It is
shown that deviation from perfect collinearity can modify properties of the
spin-orbit torque since noncollinearity generates extra Berry phase
contributions to the spin-orbit torque, which are forbidden for collinear spin
configurations. In sufficiently clean antiferromagnets, this modification can
be significant. We estimate this effect to be of relevance for fast
antiferromagnetic domain wall motion.
