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Ferroelectricity and weak ferromagnetism have been found to set on simultaneously in Ni3B7O13I at about 64°K. This is evidenced by dielectric hysteresis, spontaneous Faraday effect, quadratic magnetoelectric hysteresis, etc. The strong coupling between the mutually perpendicular spontaneous polarization—001—and spontaneous magnetization—110—is such that, when the former is reversed, the latter turns by 90°. The magnetic point group is most probably m′m2′. Dielectric constant, magnetic, and magnetoelectric susceptibilities and magnetic coercive field are shown as a function of temperature.
Ascher et al. (Tue,) studied this question.