We report on the control of electric polarization ($P$) by using magnetic fields ($B$) in a hexaferrite having magnetic order above room temperature (RT). The material investigated is hexagonal ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{1.5}{\mathrm{Zn}}_2{\mathrm{Fe}}_{12}{\mathrm{O}}_{22}$, which is a nonferroelectric helimagnetic insulator in the zero-field ground state. By applying $B$, the system undergoes successive metamagnetic transitions, and shows concomitant ferroelectric order in some of the $B$-induced phases with long-wavelength magnetic structures. The magnetoelectrically induced $P$ can be rotated 360° by external $B$. This opens up the potential for not only RT magnetoelectric devices but also devices based on the magnetically controlled electro-optical response.

• Received 11 November 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.137201