FAR-INFRARED STUDY OF FIELD-INDUCED PHASE-TRANSITIONS IN Y0.5LU0.5FEO3 AND HOFEO3 ORTHOFERRITES

Spin excitations have been studied in Y0.5Lu0.5FeO3 and HoFeO3 in magn etic fields up to 20 T at frequencies 4-84 cm(-1). Anomalies of the AF MR modes have been found in Y0.5Lu0.5FeO3 at the field-induced T-24(G( x,z)F(z,x))-->Gamma(2)(G(z)F(x)) phase transition near 13.5 T. The obs erved AFMR and rare-earth mode behaviour in HoFeO3 at H parallel to b- axis and T = 1.2 K give evidence of the ,y))-->Gamma(13)(G(y)F(y))-->G amma(34)(G(x)F(z,y)) phase transitions.