Magnetic-field control of electric polarization in a helimagnetic haxaferrite Ba₂Mg₂Fe₁₂O₂₂

A Y-type hexaferrite Ba₂Mg₂Fe₁₂O ₂₂ undergoes a transition to a proper-screw type helimagnetic structure with a propagation vector k₀ [001] at 195 K, below which the system shows field-induced successive transitions under magnetic fields up to 1 T. Magnetization measurements also indicate the presence of the conical spin structure at low magnetic fields (∼ 10 mT) below about 50 K. We report on the magnetic control of the electric polarization in Ba₂Mg ₂Fe₁₂O₂₂ with using the linearly oscillating fields up to 1 T at 5 K. The polarization vector can be cyclically reversed by weak magnetic fields of 30 mT. In addition, the polarization vector is repeatedly reversed without significant decay even by applying fields of ± 1 T, which suggests that the sense of the spin helix is somehow conserved in the process of the field-induced phase transitions. We propose that the conical spin structure carries the polarization vector upon the reversal of magnetic field.