Head-to-Head Domain Walls in Thin Magnetic Stripes

Stripes of magnetic material patterned from thin films are becoming increasingly important for technological applications such as read heads for magnetic recording and magnetic non-volatile memory. In a long, thin magnetic stripe, we expect that magnetostatic shape anisotropy will cause the magnetization to lie in either of two directions parallel to the stripe axis. Under these conditions, head-to-head (or tail-to-tail) domain walls will necessarily be formed at the interface between oppositely directed domains. We have performed micromagnetic calculations of head-to-head domain wall structures, and have found that minimization of exchange and magnetostatic energies gives rise to two basic types of head-to-head walls, `transverse' walls, where the magnetization lies transverse to the stripe axis at the center of the junction, and `vortex' walls, where a magnetization vortex forms at the center of the junction. The energy of the transverse wall is less than that of the vortex wall for the narrowest stripes in the thinnest films. The calculations suggest that the critical stripe thickness, t_crit, and width, w_crit, where the two types of domain walls have equal energies are given by t_critw_crit ≈ 130* A/μ_0M_s^2 where A is the exchange stiffness constant and M_s is the spontaneous magnetization of the material.