Imaging and Control of Surface Magnetization Domains in a Magnetoelectric Antiferromagnet

We report the direct observation of surface magnetization domains of the magnetoelectric ${\mathrm{Cr}}_2{\mathrm{O}}_3$ using photoemission electron microscopy with magnetic circular dichroism contrast and magnetic force microscopy. The domain pattern is strongly affected by the applied electric field conditions. Zero-field cooling results in an equal representation of the two domain types, while electric-field cooling selects one dominant domain type. These observations confirm the existence of surface magnetization, required by symmetry in magnetoelectric antiferromagnets.

Figure 1

(a) X-ray diffraction pattern showing the ${\mathrm{Cr}}_2{\mathrm{O}}_3(0006)$ and (00012) peaks. The ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrate contributes the (0006), (00012) diffraction features and a weak structure-factor-forbidden (0009) peak. (b) Topographic AFM image of the ${\mathrm{Cr}}_2{\mathrm{O}}_3(0001)$ film surface. (c) Height profiles along the blue and green lines of (b) parametrized by $S_1$ and $S_2$. Root-mean-square roughness of 0.17 nm is estimated in the region of $S_2$ from 0.8 to $1.6\mu \mathrm{m}$.

Figure 2

MFM images for the same scanning area as in Fig. 1b. (a) 296.0 K, (b) 299.6 K, (c) 304.9 K, and (d) 319.3 K.

Figure 3

(a)–(c) ${\mathrm{Cr}}_2{\mathrm{O}}_3\left(0001\right)$ film imaged by XMCD PEEM at the Cr $L$ edge. (a) No contrast at 584 K. (b) Multidomain state after zero-field cooling. (c) Nearly single-domain state at 223 K after magnetoelectric field cooling. (d) XMCD spectrum recorded from within one domain. The inset indicates the qualitative spin polarization in the image with respect to positively circularly polarized incident light.

Figure 4

(a) XMCD absorption at the Cr $L_3$ edge taken by left (red) and right (green) circularly polarized light from a $1\mu {\mathrm{m}}^2$ spot in the red area of Fig. 3c. (b) XMCD signal derived from (a). (c) Unoccupied spin-up states and spin-down states taken by SPIPES at 300 K. (d) Spin polarization of unoccupied states derived from (c). (e) Calculated majority-spin (red) and minority-spin (green) DOS for the ${\mathrm{Cr}}_2{\mathrm{O}}_3$ surface. The energy is referenced from the surface valence band maximum. (f) Difference of the majority-spin and minority-spin DOS from (e). The energy scales are the same in all panels, but the first majority-spin peaks are aligned (dashed lines) to remove the uncontrollable energy shifts due to different final-state effects and other uncertainties.