Head-to-Head Domain Wall Structures in Tapered Magnetic Strips

We present the calculations of head-to-head domain wall (DW) structures in magnetic nanowires of permalloy and cobalt with a tapered cross section, with average widths, W
_mid
, ranging from 60 to 300 nm, ratios of the bottom width, W
_Bottom
, to top width, W
_Top
, ranging from 1 to 2 and thicknesses, T, from 7.5 to 15 nm. In agreement with prior work, for wires with a rectangular cross section, the critical thickness and wire width W which determines whether transverse or vortex DWs are energetically favored is approximated by T · W = C · δ
²
with δ the exchange length and C a constant. When taking the slope of the tapered edge of the nanowires into account, the relation is modified by a slope-dependent term which is presented in this paper. The results provide an extended phase diagram for stable DW regimes. Furthermore, the effect of magnetocrystalline anisotropy energy is investigated which yields a more complex thickness and anisotropy energy-dependent behavior.