  For a long time, there have been no efficient ways of controlling
antiferromagnets. Quite a strong magnetic field was required to manipulate the
magnetic moments because of a high molecular field and a small magnetic
susceptibility. It was also difficult to detect the orientation of the magnetic
moments since the net magnetic moment is effectively zero. For these reasons,
research on antiferromagnets has not been progressed as drastically as that on
ferromagnets which are the main materials in modern spintronic devices. Here we
show that the magnetic moments in NiO, a typical natural antiferromagnet, can
indeed be controlled by the spin torque with a relatively small electric
current density (~5 x 10^7 A/cm^2) and their orientation is detected by the
transverse resistance resulting from the spin Hall magnetoresistance . The
demonstrated techniques of controlling and detecting antiferromagnets would
outstandingly promote the methodologies in the recently emerged
"antiferromagnetic spintronics". Furthermore, our results essentially lead to a
spin torque antiferromagnetic memory.
