  The damping of spin waves parametrically excited in the magnetic insulator
Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an
adjacent normal-metal film. The experiment is performed on a macroscopically
sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave
relaxation frequency is determined via the threshold of the parametric
instability measured by Brillouin light scattering (BLS) spectroscopy. The
application of a dc current to the Pt film leads to the formation of a
spin-polarized electron current normal to the film plane due to the spin Hall
effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG
film and, thus, changes the spin-wave damping. Depending on the polarity of the
applied dc current with respect to the magnetization direction, the damping can
be increased or decreased. The magnitude of its variation is proportional to
the applied current. A variation in the relaxation frequency of +/-7.5% is
achieved for an applied dc current density of 5*10^10 A/m^2.
