  We studied the current-induced magnetization dynamics of a domain wall
confined in a magnetic wire with bi-axial anisotropy. We showed that above the
threshold current density, breathing-mode excitation, where the thickness of
the domain wall oscillates, is induced by spin-transfer torque. We found that
the breathing-mode can be applied as a source of microwave oscillation because
the resistance of the domain wall is a function of the domain wall thickness.
In a current sweep simulation, the frequency of the breathing-mode exhibits
hysteresis because of the confinement.
