  We demonstrate the possibility to write and modulate the magnetic domain
walls in a TbFeCo single layer nanowire (300 nm width, 150 $\mu$m length). To
realize this, a tiny magnetic domain was nucleated by an Oersted field produced
by a 1.6 MHz pulse current (35 mA in amplitude, 5-40 ns in length) crossed the
wire. To write the wall to the wire, a DC current was used to drive the
nucleated domain (with two walls in two sides) to the wire in accordance with
spin-transfer torque mechanism. A critical current density of $J_c =
3.5\times10^{10} Am^{-2}$ was required to control the motion of the walls in
the wire. It was found that the size of the domain moving in the wire could be
adjusted by either external field or the length of the nucleated pulse current.
This could be considered as an important note for writing process in domain
wall spin-torque devices, especially, memory elements.
