Neutron diffraction studies on the multiferroic conical magnetBa2Mg2Fe12O22

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Abstract
Magnetic structure of a multiferroic Y-type hexaferrite Ba2Mg2Fe12O22 with helical-spin structures propagating along [001] below 195 K has been extensively studied, using polarized and unpolarized neutron diffractions under transverse magnetic fields B ($\perp${}[001]) up to 4.5 T. At zero magnetic field, a longitudinal-conical spin state was found to emerge below about 50 K, which enables the low-B control of electric polarization P. The magnetic phase diagram was investigated as a function of transverse B and coexistence of several phases with different helical-spin periodicity was confirmed at low-B region. Furthermore, by using the polarized neutron diffraction under transverse B, we verified that the ferroelectric phase with the largest P value with a commensurate k0 vector of (0, 0, 3/2) has a transverse-conical spin structure, in which the spin component perpendicular to B shows every 90\ifmmode^\circ\else\textdegree\fi{} rotation with translation along the k0 direction. The relation between the transverse-conical spin structure and P as a function of the transverse B was discussed in terms of the inverse Dzyaloshinskii-Moriya model.