MAGNETOELECTRIC EFFECT AND MAGNETIC PHASE-TRANSITIONS IN (FEXCR1-X)(2)O-3 SINGLE-CRYSTALS

The magnetoelectric effect in (FexCr1-x)(2)O-3 (x=0, 0.02, 0.05, 0.1) single crystals has been studied under a magnetic field of up to 200 k Oe. We have found that various magnetic phase transitions due to the r estructuring of the spatial spin structure and leading to radical chan ges in the magnetoelectric effect take place in substitutional alloys. We have also detected a spontaneous phase transition from a conical h elix to a cycloidal spin structure laking place at x = 0.1 and a tempe rature of 45 K. The experimental data are in agreement with the theore tical concept based on the thermodynamic model and can be accounted fo r in terms of competition among exchange energies of different modes.