The effect of field cooling on a spin-chiral domain structure in a magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22

• Spin-chiral domain structures in a magnetoelectric helimagnet, Ba0.5Sr1.5Zn2Fe12O22, were considerably affected by the field-cooling procedure.
• The field-cooling with a small magnetic field stabilizes either a left- or right-handed spin-chiral state near a cleaved crystal face perpendicular to the helical axis.

Spin-chiral domain structures near a cleaved crystal face of a magnetoelectric helimagnet, Ba0.5Sr1.5Zn2Fe12O22, were examined after various magnetic and electric field-cooling procedures by means of the scanning resonant X-ray microdiffraction technique using circularly polarized X-rays. We have found that the application of a magnetic field (1–2 k Oe) during the field-cooling procedure stabilizes one of the handedness among the two spin-chiral states (left- or right-handed screw structure) and makes nearly a single spin-chiral domain in the vicinity of the cleaved crystal face. However, it makes the degree of the spin chirality spatially inhomogeneous even within a domain. We discuss the observed field-cooling effect in terms of possible formation of spin-chiral domains with “stripe-type” domain walls accompanied by randomly-distributed ferromagnetic islands.