Magnetostrictive Domain Walls in Antiferromagnetic NiO

We report high-resolution observations of antiferromagnetic (AF) domain walls at the surface of NiO and determine the typical width of AF walls in this material to be of the order of 150 nm. We observe a number of different types of domain walls, including double walls caused by long-range interaction between walls. We describe the observed wall profiles by a model containing the exchange interaction and magnetostriction as basic ingredients. The good agreement of this model with experiment shows that the formation of walls between antiferromagnetic domains in NiO and their properties are dominated by magnetoelastic interactions.

Figure 1

Antiferromagnetic domain walls on the NiO(100) surface imaged by photoemission microscopy. The contrast between domains (a) disappears when the light polarization is parallel to a $[010]$ direction within the surface (b). In this situation, there is only contrast due to the domain walls. The walls running along $[001]$ appear brighter; walls parallel to $[0\overline{1}1]$ or $[011]$ appear darker than the inner of the domains. (c) An topography image formed from the mean PEEM intensity obtained at 871 and 872 eV shows no features which may influence the domain structure, and shows that all the features seen in (a) and (b) are of magnetic origin. The field of view is about $35\times 35\mu {\mathrm{m}}^2$.

Figure 2

Profiles through some of the domain walls observed on NiO(100); the numbers in brackets refer to the regions marked in Fig. 1b. Widths (FWHM’s) are given in nm near the profiles. (a) Wall running roughly parallel to 001; (2c) refers to the right wall in region 2, i.e., the same one as 1 at a different location. (b) Curved walls running between two $(0\overline{1}1)$ walls; the profile for (5) was offset by adding 0.02 to the branching ratio. (c) Profile for double wall. Widths derived from other profiles are given in Ref. 12.

Figure 3

Profile of a $T$ domain wall in Fig. 1b, averaged along the wall in region 1. Points, experimental data; solid line, calculated from (3) with ${\xi }_0=73\mathrm{n}\mathrm{m}$. The width (FWHM) of the AF domain wall is about 160 nm. The inset shows a schematic representation of the (001) domain wall. Double-ended arrows show orientation of the AF vector inside the DW.