Crystal Symmetry of Magnetite in Low Temperature Phase Deduced from Magnetoelectric Measurements

Abstract

Electric polarization of magnetite, induced by rotating magnetic field in the triclinic b c plane, was measured along the triclinic a axis below 60 K where magnetite is ferrimagnetic as well as ferroelectric. The magnetoelectric polarization was influenced by the way of application of mechanical stress onto the single crystal. Mechanism of this phenomenon was discussed on the basis of the formation of twins including new types. Point group of the crystallographic symmetry of the magnetoelectric single phase was analyzed. It was shown that the present experiment was not inconsistent with the fact that among three crystalline angles, in addition to the a c , at least the b c is not right-angle. Thus magnetite in the temperature range, 4.2 K to 35 K, is of triclinic 1 , irrespective of the magnitude of the angle a b .