SPIN-DENSITY-WAVE AND FIELD-INDUCED PHASE-TRANSITIONS IN MAGNETOELECTRIC ANTIFERROMAGNETS

An investigation was done of the field induced phase transition from t he spatially modulated spin structures to the homogeneous antiferromag netic state in magnetic ferroelectrics R(x)Bi(1-x)FeO(3) (R = La, Nd) and magnetoelectrics FexCr2-xO3 in pulsed magnetic field up to 30 T. I t has been found that this transition is accompanied by a large change in the magnitude of the magnetoelectric effect. In contrast to the R( x)Bi(1-x)FeO(3), where the linear magnetoelectric effect appears in st rong magnetic fields (H > H-c) in FexCr2-xO3 such effect exists in the low-field phase (H < H-c). This is associated with the different char acter of the spatially modulated spin structure in these materials (cy cloid structure in R(x)Bi(1-x)FeO(3) and cone spiral in FexCr2-xO3).