Current-driven periodic domain wall creation in ferromagnetic nanowires

We predict the electrical generation and injection of domain walls into a ferromagnetic nanowire without the need of an assisting magnetic field. Our analytical and numerical results show that above a critical current ${j}_c$ domain walls are injected into the nanowire with a period $T\ensuremath{\sim}{(j\ensuremath{-}{j}_c)}^{\ensuremath{-}1/2}$. Importantly, domain walls can be produced periodically even in a simple exchange ferromagnet with uniaxial anisotropy, without requiring any standard ``twisting'' interaction such as Dzyaloshinskii-Moriya or dipole-dipole interactions. We show analytically that this process and the period exponents are universal and do not depend on the peculiarities of the microscopic Hamiltonian. Finally we give a specific proposal for an experimental realization.