Commensurate transverse helical ordering in the room-temperature magnetoelectric Co2Z hexaferrite

Using single crystal neutron diffraction, we confirmed the existence of the commensurate transverse helical ordering in ${Ba}_{0.52}{\text{Sr}}_{2.48}{Co}_2{Fe}_{24}{O}_{41}$ upon zero-field cooling, in which room-temperature magnetoelectric coupling has been previously observed. Its magnetic structure remained commensurate to the lattice under the external field perpendicular to the $c$ axis. We also found the commensurate ordering to be directly responsible for the electric polarization, which is the common feature of many types of hexaferrites independently of their zero-field orderings.