Multiferroic oxides with multiple magnetic order parameters and domain structures

In this presentation, we show selective observations of multiple magnetic order parameters and domain structures in multiferroic oxides with peculiar incommensurate spiral magnetic ordered states accompanying commensurate (anti)ferromagnetic ordered ones. Examples of such multiferroic oxides are hexaferrites (e.g., Ba_1.3Sr_0.7CoZnFe₁₁AlO₂₂) showing the so-called alternating longitudinal conical structure [Ueda et al., Appl. Phys. Lett. 109, 182902 (2016)] and olivine-type manganese germanate Mn₂GeO₄ showing canted antiferromagnetic conical spin chains [Honda, White et al., Nat. Commun. 8, 15457 (2017)]. For the observations, we adopted single-crystal measurements of scanning resonant x-ray microdiffraction for the hexaferrites or (un)polarized neutron scattering for the manganese germanate. These techniques clarify multiple magnetic order parameters and domain structures and their manipulations by external stimuli such as magnetic and electric fields in these peculiar multiferroic oxides. Furthermore, we show our recent research activity on exploration for new magnetoelectrics.