Control of ultranarrow Co magnetic domain wall widths in artificially patterned H-bar structures

Micromagnetic simulations of Co domain walls on nanometer crossbars that join two oppositely magnetized parallel legs of “H” shaped patterns are studied. The crossbar domain walls can twist in the plane of the H-pattern, out of the plane, or swirl, forming Neel, Bloch, or vortex structures, respectively, depending on the initial configurations. An energy phase diagram as a function of the crossbar constriction yields the Neel wall as the energetically most favorable, followed by the Bloch wall, which becomes unstable and changes into a vortex-like wall with increasing crossbar size. Most interestingly, the Neel wall width can either shrink or expand depending on the crossbar dimensions. In the case that both the crossbar length and width are small, desirable, ultranarrow domain walls can be obtained. These findings are useful for spintronic device design based on domain wall pinning via nanonotch and domain-wall magnetoresistance approaches.