We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain BFO/ crystal at low temperature. The modes soften close to the critical field of 18.8,T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31,T. A microscopic model that includes two DM/ interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.
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