Field-induced spin reorientation in the antiferromagnetic Dirac material EuMnBi2 revealed by neutron and resonant x-ray diffraction

Field-dependent magnetic structures of a layered Dirac material EuMnBi2 were investigated in detail by the single crystal neutron diffraction and the resonant x-ray magnetic diffraction techniques. On the basis of the reflection conditions in the antiferromagnetic phase at zero field, the Eu moments were found to be ordered ferromagnetically within the ab plane and stacked antiferromagnetically along the c axis in the sequence of up-up-down-down. Upon the spin-flop transition under the magnetic field parallel to the c axis, the Eu moments are reoriented from the c to the a or b directions forming two kinds of spin-flop domains, whereas the antiferromagnetic structure of the Mn sublattice remains intact as revealed by the quantitative analysis of the change in the neutron diffraction intensities. The present study provides a concrete basis to discuss the dominant role of the Eu sublattice on the enhanced two-dimensionality of the Dirac fermion transport in EuMnBi2.