  We discuss the possibility to generate, manipulate, and probe single spins in
single-level quantum dots coupled to ferromagnetic leads. The spin-polarized
currents flowing between dot and leads lead to a non-equilibrium spin
accumulation, i.e., a finite polarization of the dot spin. Both the magnitude
and the direction of the dot's spin polarization depends on the magnetic
properties of leads and their coupling to the dot. They can be, furthermore,
manipulated by either an externally applied magnetic field or an intrinsically
present exchange field that arises due to the tunnel coupling of the
strongly-interacting quantum-dot states to spin-polarized leads. The exchange
field can be tuned by both the gate and bias voltage, which, therefore, provide
convenient handles to manipulate the quantum-dot spin. Since the transmission
through the quantum-dot spin valve sensitively depends on the state of the
quantum-dot spin, all the dynamics of the latter is reflected in the transport
properties of the device.
