Domain wall properties in constrained geometries

For almost a century, the width of magnetic domain walls (DW) has been believed to be determined by material properties only. However, recent investigations of DWs in nanometer-scale systems have revealed new physical properties caused by the geometrical confinement of the magnetization and particularly by the ability of constraining DWs to very small widths. Both for a basic understanding and potential applications, it is important to understand quantitatively how DW properties can be modified by means of geometry.

For instance, we have studied magnetic 180° Néel domain walls pinned in micron-sized Fe20Ni80 elements containing geometrical constrictions (Figure 1) by spin-polarized scanning electron microscopy and numerical simulations. The confinement results in a strong reduction of the width of 180° Néel walls compared to unconstrained systems. For a 7.5-nm-thick sample, the wall width in the extended film is measured to be 700 nm. This is reduced to 100 nm in a 10 µm × 4 µm element with contriction dimensions of 100 nm × 500 nm (Figure 2).

We have furthermore shown how, by controlling the constriction dimensions, the wall width can be tailored and the type of wall modified.

[1] P.-O. Jubert, R. Allenspach, and A. Bischof, Phys. Rev. B 69, 220410(R) (2004).