MAGNETOELECTRIC EFFECT AND TOROIDAL ORDERING IN GA2-XFEXO3

The field dependence of the magnetoelectric effect and longitudinal ma gnetostriction of Ga2-xFexO3 single crystals is studied In magnetic fi elds up to 200 kOe in the temperature range from 4.2 to 300 K. It: is shown that the magnetoelectric effect in these materials is determined mainly by the toroidal moment T and is not related to magnetostrictio n, as was previously theorized. A new method for determining the toroi dal moment by measuring the electric polarization in a strong magnetic held is proposed. The value of the toroidal moment of the unit cell i n Ga1.15Fe0.85O3 is calculated: T = (T-a, 0, 0), where T-a = 24.155 mu (B) Angstrom per unit cell. Experimental data are analyzed using a the ory of toroidal spin ordering, which gives good agreement with experim ent. (C) 1998 American Institute of Physics.