Effects of nanostructuring and substrate symmetry on antiferromagnetic domain structure in LaFeO${}_3$ thin films

The antiferromagnetic domain structure in LaFeO${}_3$ thin-film epilayers grown on La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ is imaged combining linearly polarized x-ray-absorption spectroscopy with photoemission electron microscopy. Detailed analysis of polarization-dependent domain contrast from magnetic dichroism reveals two sets of symmetrically different antiferromagnetic easy axes in the LaFeO${}_3$ layer along the in-plane $\langle 110\rangle$ and $\langle 100\rangle$ crystalline axes (pseudocubic notation), respectively. We show that extended antiferromagnetic domains can be stabilized selectively for nanowires defined in this perovskite thin-film system along either orientation of the easy axes. The results demonstrate how the equilibrium domain structure of thin-film nanoscale antiferromagnets depend on a combination of substrate symmetry, nanowire dimensions, and in-plane crystalline orientation.

Figure 1

(a) XMLD-PEEM images showing the same 5-μm × 5-μm blanket region for three polarization angles. A region showing uniform contrast for ω $=$ 90° is outlined as a guide to the eye. (b) Recorded XMLD intensity vs polarization angle ω. The measurement geometry is illustrated in the inset. (c) Distribution of $\langle 110\rangle$- and $\langle 100\rangle$-oriented AFM domains as a function of LFO thickness. The inset shows the relative XMLD signal vs LFO layer thickness.

Figure 2

Linear $q_x$ scans of the (−204)${}_{\mathrm{pc}}$ and (204)${}_{\mathrm{pc}}$ reflections in thin films and substrate for (a),(b) LFO (100 u.c.)/LSMO (50 u.c.)/Nb:STO and (c),(d) LFO (100 u.c.)/Nb:STO. The peaks are all fitted using pseudo-Voigt curves (solid lines).

Figure 3

(a) Schematic of the embedded nanostructures and the pattern layout. (b)–(d) XMLD-PEEM micrographs of the AFM domain structure of zigzag line patterns defined in LFO (10-u.c.)/LSMO (90-u.c.) bilayers with (b) 2-μm, (c)1-μm, and (d) 500-nm linewidths. The experimental geometry is illustrated in the inset in the lower left corner of each XMLD-PEEM image.

Figure 4

XMLD-PEEM images of 100-nm-wide zigzag nanostructures defined in an LFO (10-u.c.)/LSMO (90-u.c.) bilayer; (a) with the nanostructure edges parallel to the in-plane $\langle 110\rangle$ axes, and (b) with the edges parallel to the in-plane $\langle 100\rangle$ axes, recorded with x-ray polarization angles (a) ω $=$ 90° and (b) ω $=$ 40°.