  Pure spin currents transport angular momentum without an associated charge
flow. This unique property makes them attractive for spintronics applications,
such as torque induced magnetization control in nanodevices that can be used
for sensing, data storage, interconnects and logics. Up to now, however, most
spin transfer torque studies focused on metallic ferromagnets, while magnetic
insulators were largely ignored, in spite of superior magnetic quality factors.
Here, we report the observation of spin torque-induced magnetization dynamics
in a magnetic insulator. Our experiments show that in ultrathin magnetic
insulators the spin torque induced magnetization dynamics can be substantially
larger than those generated by the Oersted field. This opens new perspectives
for the efficient integration of ferro-, ferri-, and antiferromagnetic
insulators into electronic devices.
